Halogen Derivatives of the Aliphatic Hydrocarbons

Chapter 3

Halogen Derivatives of the Aliphatic Hydrocarbons W. K. R. MUSGRAVE

Halogen derivatives of both saturated and unsaturated aliphatic hydrocarbons are known in which one or more hydrogen atoms are replaced by halogen atoms up to complete substitution. In di- or poly-halogeno compounds the halogen atoms need not be the same; many compounds containing three different halogens are known. These compounds are subdivided into mono-, di-, tri- and poly-halogenoparaffins, halogenated olefins and halogenated acetylenes, each class being dealt with separately. 1. Halogenated paraffins

(a) Monohalogenopara~ns. Alkyl halides. Halogenoalkanes, CnH~n+zX The alkyl halides may be regarded as the monohalogen derivatives of the paraffins or as esters formed between alcohols and the halogen acids. As with the paraffins themselves, branching of the alkyl group leads to isoYnerism

R~ and the occurrence of primary, RCH~X, secondary, a|kyl haHdes

R~ R'---CX. R,,/

CHX, and tertiary R '/

CH3

CH3F

C9H5C1

CH3~ CHBr CH3/

Methyl fluoride (fluoromethane)

Ethyl chloride, (chloroethane)

Isopropyl bromide, (2-bromopropane)

J

CH3uC--I

tert-Butyl iodide (2-iodo-2-methylpropane)

I

CH8

(i) Pre#aration (I) By replacement of hydrogen. (a) Direct halogenation of the paraffins, a free radical process catalysed by heating or by u.v. irradiation, has already

I

MONOHALOGENOPARAFFINS

479

been discussed (pp. 313,379). As a preparative method it is not generally used since, although the rate of reaction increases through the series primary H, secondary H, tertiary H, and also as the halogen changes from bromine to chlorine to fluorine, the divisions are not clear-cut and mixtures of isomers result as well as mixtures of mono- and poly-substitution products (P. C. Anson, P. S. Fredricks and J. M. Tedder, J. chem. Soc., 1959, 918). Direct substitution by iodine does not usually occur probably owing to the powerful reducing action of the hydrogen iodide formed: C3H 8 + 19. ~ C3H~I + HI

In the presence of substances capable of uniting with or decomposing hydriodic acid (such as iodic acid and mercuric oxide) substitution can take place: 5C3H8 + 213 + HIO3 = 5C3H7I + 3H20

2C3H8 + 2I, + HgO = 2C3H~I + H20 + Hglz

(b) Free radical chlorination can also be effected by sulphuryl chloride in the presence of benzoyl peroxide (see pp. 321,381). (2) By addition of halogen acids to olefins. Normally this is an electrophilic addition reaction and the direction of addition can be predicted from a consideration of the inductive and hyperconjugative effects of the alkyl groups attached to the olefinic bond (cf. p. 300). The order of reactivity of the hydrogen halides is HI > HBr > HC1 > HF. Aqueous solutions of hydriodic or hydrobromic acid can often be used; hydrogen chloride is used in an anhydrous solvent like glacial acetic acid and hydrogen fluoride as the anhydrous liquid (see W. J. Hickinbottom, "Reactions of Organic Compounds", Longmans, London, 1945, p. 17; A. M. Lovelace, D. A. Rausch and W. Postelnek, "Aliphatic Fluorine Compounds", Reinhold, New York, 1958, p. 12): CHsCH = C H ~ He-+ CHsCH__CH 3 I~_~ CH3CHICH 8

Olefins react with hydrogen bromide in this way only when the reagents are quite pure and no trace of peroxide is present; hence the presence of air must also be avoided. When peroxide, or any source of free radicals, is present a rapid chain reaction occurs with a reversal of the normal addition (M. S. Kharasch, H. Engelmann and F. R. Mayo, J. org. Chem., 1937, 2, 288) (cf, pp. 3Ol, 315): CH3CH=CH.. + Br . . . . > CH3CHCH~Br CH3CHCH2Br + HBr

~ > CH3CHzCHzBr + Br.

480

HALOGENATED ALIPHATIC HYDROCARBONS

3

This is known as the Peroxide Effect and applies only to hydrogen bromide. (3) From alcohols with (a) Halogen acids. The reactivities of the acids are in the order HI > HBr > HC1. Hydrogen fluoride is not generally used because alkyl fluorides are unstable in the presence of aqueous hydrofluoric acid and water is formed during this reaction. The alcohols react in the order tertiary > secondary > primary, consequently tertiary halides are formed easily, usually in the cold, by reacting the alcohol with aqueous hydrogen halide (J. F. Norris and A. W. Almsted, Org. Synth. Coll. Vol. I, 1941, p. 144; F. C. Whitmore et al., J. Amer. chem. Soc., 1933, 55, 361,406, 1559). Secondary bromides and iodides can usually be prepared in the same way (M. S. Kharasch, C. Walling and F. R. Mayo, ibid., 1939, 6i, 1559; H. J. Lucas, T. P. Simpson and J. M. Carter, ibid., 1925, 47, 1462; H. A. Shonle, A. K. Keltch and E. E. Swanson, ibid., 193o, 52, 2440) but to prepare the chloride it is better to add zinc chloride as a catalyst, as in the preparation of primary alkyl chlorides (J. E. Copenhaver and A. M. Whaley, Org. Synth., Coll. Vol. I, 1941, p. 142). Heating must be for as short a time as possible in all cases since it may cause isomerisation. Primary alkyl bromides are prepared using aqueous hydrobromic acid and sulphuric acid (0. Kamm and C. S. Marvel, ibid., Coll. Vol. I, 2nd Edition 1948, pp. 25-29) or by saturating the alcohol at lOO-12o 0 with dry hydrogen bromide (E. E. Reid, J. R. Ruhoff and R. E. Burnett, ibid., Vol. II, 1943, p. 246). Good yields of primary, secondary, and tertiary alkyl iodides are obtained by refluxing the alcohols or ethers with potassium iodide and 95 % phosphoric acid (H. Stone and H. Shechter, J. org. Chem., 195o, 15, 491) : R O H + K I + H3PO 4 -- R I + KH2PO 4 + H20

(b) Phosphorus haIides. Phosphorus pentachloride (G. A. Lutz et al., J. Amer. chem. Soc., 1948, 7o, 4135), phosphorus tribromide, red phosphorus and bromine (C. R. Noller and R. Dinsmore, Org. Synth., Coll. Vol. II, 1943, p. 358), phosphorus triiodide, and red phosphorus and iodine (H. S. King, ibid., p. 399) will all react readily with the appropriate alcohols to give primary, secondary and tertiary halides. With phosphorus trichloride, esters of phosphorous acid are formed (H. McCombie, B. C. Saunders and G. J. Stacey, J. chem. Soc., 1945, 38o), and the yield of alkyl chloride is rarely more than 50 %. (c) Thionyl chloride or thionyt bromide. The lower primary and secondary alcohols yield the chloride best by reaction with thionyl chloride in the presence of pyridine or dimethyl- or diethyl-aniline (G. Darzens, Compt. rend., 1911, 152, 1314, 16Ol; A. McKenzie and T. M. A. Tudthorpe, J. biol. Chem., 1924, 62, 551; H. Gilman andA. P. Hewlett, Rec. Trav. chim., 1932, 5x, 93) :

I

MONOHALOGENOPARAFFINS

481

CsHIiOH + SOC19 + CsHsN = CsHnCI + SO9 + CsHsN'HCI

The reaction proceeds via the alkyl sulphite. Tertiary alcohols give the alkyl chlorides direct. (d) Alkyl, aralkyl or aryl phosphites and a halide. Triphenyl phosphite, the halogen compound (e.g. an alkyl iodide, a bromide or carbon tetrachloride) and the alcohol, are refluxed for 24-48 hours (H. N. Rydon and S. R. Landauer, B.P., 695,468/1957). The reaction proceeds more rapidly when a hydrogen halide is used (idem, B.P., 698,699/1957). Alternatively the phosphite ester, alcohol and halogen (C12, Br 2 or Is) can be used, or the triphenyl phosphite dihalide may be prepared separately, and treated with the alcohol; the latter method gives 65-95 ~/o yields in one hour at room temperature (D. G. Coe, S. R. Landauer and H. N. Rydon, J. chem. Soc., 1954, 2281): (PhO)3P + X2

ROH

+ (PhO)sPX s

> (PhO)3PX z

.#O > R X + (PhO)sP + PhOH ~X

(4) From alkyt esters and metallic halides. (a) Sulphates. Ethyl bromide is obtained from ethyl hydrogen sulphate and potassium bromide, or simply from a mixture of ethyl alcohol, sulphuric acid and potassium bromide (A. Holt, J. chem. Soc., 1916, lO9, I). Alkyl sulphates and hydrogen bromide in the vapour phase yield alkyl bromides (I.G., G.P., 574,833/1933 ). Methyl and ethyl sulphates react readily with alkali iodides in aqueous solution to yield the corresponding alkyl iodide. (b) Alkyl methane- and p-toluene-sulphonates are converted into fluorides in good yields on heating with anhydrous potassium fluoride, usually in ethylene glycol or diethylene glycol (W. F. Edgell and L. Parts, J. Amer. chem. Soc., 1955, 77, 4899; F- L. M. Pattison and J. E. Millington, Can. J. Chem., 1956, 34,757)-They also give iodides with sodium iodide (R.S. Tipson, M. A. Clapp and C. H. Cretcher, J. org. Chem., 1947, 12, I33), and bromides with sodium bromide (H. Pines, A. Rudin and V. N. Ipatie~, J. Amer. chem. Soc., 1952, 74, 4063). (c) Chloroformic esters, prepared from the alcohol and phosgene, give fluoroformates with thallous fluoride which decompose on warming in pyridine to carbon dioxide and alkyl fluorides in 60-75 ~/oyields (S. Nakanishi, T. C. Myers and E. V. Jensen, ibid., 1955, 77, 3099): ROH + COCI~

> ROCOC1~

ROCOF

> RF + CO~

482

HALOGENATED ALIPHATIC HYDROCARBONS

3

(5) Halogen exchange. Chlorides and bromides can be converted into iodides by heating with sodium iodide in acetone or a higher ketone (H. Finketstein, Bet., 191o, 43,1528). Yields vary between 60 ~/o and quantitative. Methyl alcohol has been used as solvent in the conversion of bromides to iodides (M. Schirm and H. Besendorf, Arch. Pharm., 1942, 28o, 64): NaI C5HnCHBrCHa MeOH > CsHnCHICH3 (75%)

Chlorides, bromides and iodides give fluorides, in good yields, when heated, preferably with anhydrous potassium fluoride, in ethylene glycol or diethylene glycol (F. L. M. Pattison and J. J. Norman, J. Amer. chem. Soc., 1957, 79, 2311; H. Kitano and K. Fukui, J. chem. Soc., Japan, Ind. Chem. Sect., 1955, 58, 352). Mild fluorinating agents (AgF, HgF, HgF~ or red mercuric oxide and anhydrous hydrogen fluoride) are used to convert alkyl chlorides, bromides and iodides into alkyl fluorides (see A. M. Lovelace, D. A. Rausch and W. Postelnek, "Aliphatic Fluorine Compounds", Reinhold, New York, 1958, pp. 1-6 and A. K. Barbour, L. J. Belf and M. W. Buxton, in "Advances in Fluorine Chemistry", Vol. 3, Butterworths, London, 1963). (6) From the silver salts of carboxylic acids (Hunsdiecker Reaction). The anhydrous silver salt is treated with at least an equimolar amount of halogen (CI,, Br~, or Is) sometimes in solution (benzene, carbon tetrachloride, petroleum ether) and at widely varying temperatures depending on the reagents used (C. V. Wilson, Org. Reactions, 1957, 9, 332): R C O z A g + Xz

RCOsX

- > RCOg.X + A g X

> R E + CO s

(7) From amines. (a) The corresponding primary and secondary amines can be converted into alkyl halides by treating their benzoyl derivatives with phosphorus pentachloride or pentabromide and distilling the resultant benzamido- or benzimino-halide (J. von Braun and W. Sobecki, Ber., 1911, 44, 1464): RNH~

> RNHCOC6H 5 - - - + R N = CC1CsH5

> RC1 + CeH5CN

(b) Distillation of trimethylamine hydrochloride at 285 ~ yields methyl chloride, dimethylamine and trimethylamine (C. Vincent, Compt. rend., 1877, 85, 1139). Alkylaniline hydrochlorides and hydrobromides similarly give alkyl chlorides and bromides (W. J. Hickinbottom et al., J. chem. Soc., 193o, 1566; 1931, 1281; 1932, 2396).

I

MONOHALOGENOPARAFFINS

483

(8) From organometallic compounds. Organometallic compounds react with halogens (Clz, Brz and I,) to give organic halides: RHgC1 + C1z ----> RC1 + HgClz RMgBr + I S ~

RI + MgBrI

The reaction with iodine can be used to give a rough estimate of the concentration of a Grignard reagent (H. Gilman, "Organic Chemistry", Vol. I, 2nd. Edition, John Wiley & Sons, New York, 1944, p. 500; F. C. Whitmore, E. L. Whittle and B. R. Harriman, J. Amer. chem. Soc., 1939, 6i, 1585). Alkali metal alkyls will react with organic halides in halogen-metal interconversion reactions to give alkyl halides (R. G. Jones and H. Gilman, Org. Reactions, 1951, 6, 339): BuLi + RBr---> BuBr + Lil~ (9) By addition of lower aIkyl halides to olefins. This reaction takes place in the presence of aluminium chloride (L. Schmerling, J. Amer. chem. Soc., 1945, 67, 1152): (CHa)aC1 + CH~=CHi

>

(CHa)aCHgCH~C1

It is best to use tertiary alkyl halides since primary and secondary halides isomerise under the conditions employed.

(ii) Properties and reactions Alkyl halides are ethereal, sweet-smelling compounds, very slightly soluble in water but readily soluble in organic solvents. Alkyl fluorides with even numbers of carbon atoms are highly toxic (F. L. M. Pattison and J. J . Norman, ibid., 1957, 79, 2311) presumably because they are oxidised in the body to monofluoroacetic acid (R. Peters, Endeavour, 1954, 5I, I47), whereas those with an odd number of carbon atoms cannot be so degraded. The lower members e.g. methyl, ethyl, n- and iso-propyl fluorides, methyl and ethyl chlorides, and methyl bromide are gases at room temperature; the remaining common ones are liquids. The chlorides boil 28-2o o lower than the bromides, and the latter 34-28 o lower than the corresponding iodides. These differences grow less with increasing molecular weight. As in the case of the paraffins, here also, when isomers exist, the normal members have the highest boiling points; the more branched the carbon chain, the lower is the boiling point (see Table I). Heat causes isomerisation especially in presence of metallic halide catalysts. Either iso- or tert-butyl bromide gives an equilibrium mixture containing 8o % of the tert-bromide (A. Michael and F. Zeidler, Aim. 1912, 393, 81; A.

484

HALOGENATED

ALIPHATIC

TABLE

HYDROCARBONS

3

1

B O I L I N G P O I N T S OF SOME A L K Y L H A L I D E S

Radical

Formula

Fluoride Chloride b.p. b.p.

Methyl Ethyl n-Propyl Isopropyl n-Butyl Isobutyl see-Butyl

Bromide Iodide b.p. b.p.

CH sCgH6" CH3.CHg-CH ~. (CH3)gCH" CH 3" (CH9)3" (CHs)~CH" CH~" C9H5" CH(CH3) 9 tert-Butyl (CH3)3C" n-Amyl CH 3.(CH2) 4Isoamyl (CH3)zCH-CH~CH 2. 1-Ethyl-n-propyl (C9H5)9CH . . 1-Methyl-n-butyl C8H7. CH(CH3) 9 1,2-Dimethyl-n-propyl (CHs)~CH.CH(CH3). tert-Pentyl CgH5.C(CH3) ~" n-Hexyl CH 8. (CH~)5 9 C H 3. (CH2) 6. n-Heptyl n-Octyl CH 3. (CHa) 7.

--78"40 --24-090 3"450 --38.00 +12.50 38.40 - - 3.2 o 46.6 o 71-0 o - - 9"4 o 34"8 o 59-40 32" 5 o 78.50 101- 5 o -68-8 o 91.4 o 25.1 ~ 68.2 ~ 91.20 12.1 o 50.70 73.2 o 62.80 106.0 o 129.00 53.50 100.0 ~ 120.60 . . 50.00 104.00 113.00 -91"0 ~ 115.00 44.80 86-00 100.0 ~ 93.40 133.0 ~ 155.0 ~ 119.7 o 159- 0 ~ 180.0 ~ 142.80 180"0 o 201.5 o

Cetyl Myricyl

b.p. 287.0 ~ --

CteH33. C30H61-

m.p. --

64.0 ~

m.p. 15.0 ~ --

42.50 72.40 102.5 o 89.5 o 130.4 o

121.0 ~ 120.0 ~ 103.30 155.00 148.0 o 145.0 ~ 144.00 138.00 127.00 179.00 203- 90 225" 50 m.p. 22" 00 70" 0 ~

Michael, E. Schar/ and F. Voigt, J. Amer. chem. Soc., 1916, 38, 653). O t h e r chlorides and bromides, including isobutyl chloride, iso- and tert-amyl bromides, iso- a n d n-propyl bromides, isomerise on heating in t h e presence of b a r i u m or t h o r i u m chlorides or b r o m i d e s (P. Sabatier and A. Maithe, Compt. rend., 1913, 156, 658). T h e r e a c t i v i t i e s of t h e a l k y l h a l i d e s in v a r i o u s r e a c t i o n s are in t h e o r d e r iodides > b r o m i d e s > c h l o r i d e s > fluorides a n d t e r t i a r y > s e c o n d a r y > p r i m a r y . F o r s o m e t i m e fluorides were r e g a r d e d as b e i n g p a r t i c u l a r l y u n s t a b l e b u t t h i s i n s t a b i l i t y o n l y applies in t h e p r e s e n c e of h y d r o g e n ion (A. M . Lovelace et al., " A l i p h a t i c F l u o r i n e C o m p o u n d s " , R e i n h o l d , N e w Y o r k , 1958, p. 12) a n d t h e y are m o r e s t a b l e t o t h e u s u a l nucleophilic r e a g e n t s t h a n t h e c o r r e s p o n d i n g chlorides (F. W. Hogmann, J. org. Chem., 195o, 15, 425; R. E . Parker, in " A d v a n c e s in F l u o r i n e C h e m i s t r y " , Vol. 3, B u t t e r w o r t h , L o n d o n , 1963). T h e m a i n r e a c t i o n s are nucleophilic substitutions w h i c h c a n occur b y u n i m o l e c u l a r or b i m o l e c u l a r m e c h a n i s m s d e p e n d i n g on t h e s o l v e n t a n d t h e s t r u c t u r e of t h e a l k y l g r o u p (see Banthorpe, this Vol., p. 270; C. K. Ingold, " S t r u c t u r e a n d M e c h a n i s m in O r g a n i c C h e m i s t r y " , G. Bell & Sons, L o n d o n , 1953, p. 308): RI

+ 0 H

e

=~ROH

+I

e

I

MONOHALOGENOPARAFFI NS

485

Nucleophiles other t h a n OH e which will react in this way are CN e, CH3CO0 e, (CH3) 3N, N3 e, CsHsN, (CH3) 2S, C~HsO e, NH3, NOs e, SH e. On a preparative scale, hydrolysis to the alcohol is usually carried out by aqueous alkali but primary and secondary halides can be hydrolysed by heating with water at N i oo 0. Tertiary halides hydrolyse more readily. In all cases some olefin is formed by elimination processes particularly in the case of the tertiary halides where the intermediate is usually a carbonium ion which can easily lose a proton to give the olefin. If the olefin is desired as a main product it is usual to treat the alkyl halide with alkali containing a trace of water, alcoholic alkali or a tertiary amine (J. C. Hessler, Org. Synth. Coll. Vol. I, 1941, p. 438; M. L. Sherrill, B. Otto and L. W. Pickett, J. Amer. chem. Soc., 1929, 5 I, 3028; A. Klages and S. Heilmann, Ber., 19o4, 37, I447), the stronger nucleophile encouraging elimination at the t5 position as well as substituting at the a position. In the case of optically active halides, bimolecular substitution is accompanied by inversion while unimolecular substitution involves racemisation. Nucleophilic reactions between alkyl halides and alkali metal derivatives of malonic ester, acetoacetic ester and fl-diketones result in replacement of the acidic hydrogen atoms of the methylene groups (H. A. Shonle, A. K. Keltch and E. E. Swanson, J. Amer. chem. Soc., 193 o, 52, 2440), e.g. : COzEt e/CO~Et C9H5I + CH ~COgEt

I

>

C~Hs--CH

+ Ie

I

CO,Et Alkyl halides and metals can react by free radical m e c h a n i s m s to form alkyl-metal compounds. W i t h sodium the i n t e r m e d i a t e alkylsodium imm e d i a t e l y reacts with more alkyl halide to give an alkane b y nucleophilic substitution: CH3I + Na. > NaI + CH 3. CH 3. + Na.:

CH3Na + CH3I

> CH3Na

> CH3--CH 3 + NaI

For further d a t a on these W u r t z reactions see M. Faillebin, Bull. Soc. chim. Ft., 1924 [iv], 35, 16o; H. F. Lewis et al., J. Amer. chem. Soc., 1928, 50, 1993, and this Vol., p. 361 et seq. Since alkyl-lithiums are m u c h less reactive t h a n alkylsodiums they can be p r e p a r e d by direct action oi l i t h i u m on the alkyl b r o m i d e (R. G. Jones and H. Gilman, Org. Reactions, 1951, 6, 339): CHs(CH~)3Br + Li.

~> LiBr + C H 3 C H g C H ~ C H g .

Li

-~ CHs(CH~).aLi

486

HALOGENATED ALIPHATIC HYDROCARBONS

3

O t h e r m e t a l s or their alloys react similarly, as in the formation of Grignard reagents, m e r c u r y and zinc derivatives etc. (cf. this vol., Chapt. VII).The reaction is of particular commercial i m p o r t a n c e in the m a n u f a c t u r e of tetraethyl-lead for use as an additive to petrol: RI + -Mg.

~ R. + .MgI

> R--Mg--I

In these reactions with metals, alkyl iodides and bromides are most often used, the chlorides are sometimes too unreactive and the fluorides either do not react or are decomposed at the temperature required to initiate reaction. There appear to be three general m e t h o d s for the reduction of alkyl halides (a) using hydrogen and a c a t a l y s t ; (b) using a source of " n a s c e n t " hydrogen and (c) using lithium hydride or lithium aluminium hydride. Examples of method (a) are reduction of (i) cetyl iodide to cetane by hydrogen and palladised calcium carbonate (P. C. Casey and J. C. Smith, J. chem. Soc., 1933, 346) and (ii) alkyl fluorides using palladised carbon (J. R. Lacher et al., J. phys. Chem., I956, 6o, I454) : n-PrF

~ n-C3H8

Other techniques, for example those using palladium asbestos in acetone (cf. R. R. Aitken, G. M. Badger and J. W. Cook, J. chem. Soc., 195o, 331) and platinum or palladium on barium sulphate (cf. K. W. Rosenmund and F. Zetsche, Ber., 1918, 51, 578), could no doubt be used. In method (b) zinc is most commonly used; with aqueous alcohol (cf. N. Zelinsky, Ber., 19Ol, 34, 28Ol); as palladised zinc with hydrochloric acid (idem, Ber., 1898, 31, 3203); with acetic acid and hydrogen chloride e.g. to reduce cetyl iodide (P. A. Levene, Org. Synth. Coll. Vol. II, p. 32o) or with acetic acid alone (Casey and Smith, loc. cir.). With the last reagent the reduction of the alkyl bromide was incomplete. Zinc and hydrogen chloride have been used to reduce t e r t i a r y iodides (F. C. Whitmore and H. P. Orem, J. Amer. chem. Soc., 1938, 60, 2573). The use of a zinc/copper couple with either methyl alcohol or ethyl alcohol for the reduction of alkyl iodides is described in most elementary practical books (see also Casey and Smith, loc. cir.). Method (c) has been used to reduce chlorides, bromides and iodides; an ether is used as solvent with 5-15 % excess of lithium aluminium hydride (W. G. Brown, Org. Reactions, 1951, 6, 469). Hydrogen iodide can also be used as a reducing agent (C. I. Bickel and R. Morris, J. Amer. chem. Soc., 1951, 73, 1786) and any alkyl halide which will form a Grignard reagent can be converted into the hydrocarbon by treatment of this reagent with a compound containing active hydrogen: n-BuBr Mg_~n-BuMgBr. H'~

n-C,H,, + Mg(OH)Br

I

MONO

HALOGENOPARAFFINS

487

(C. D. Hurd and J. L. Azorlosa, ibid., I95I, 73, 33; J. Cason and R. L. Way, J. org. Chem., 1949, x4, 3I).

(iii) Individual corn~ounds Methyl fluoride, ~quoromethane, CH3F, b.p. N 7 8 . 4 ~ f.p. - - 1 1 4 . 8 ~ is prepared by interaction of methyl iodide, iodine, and mercurous fluoride (F. Swarts, Bull. Soc. chim. Belg., 1937, 46, IO). It is also formed b y heating tetramethylammonium fluoride (J. N. Collie, J. chem. Soc., 19o4, 85, I317), and b y reacting potassium fluoride with methyl p-toluenesulphonate alone or in diethylene glycol solution. (W. t 7. Edgell and L. Parts, J. Amer. chem. Soc., 1955, 77, 4899) 9Methyl chloride, chloromethane, f.p. --97" 7 ~ is obtained from methane or methyl alcohol. It is a sweet-smelling gas, soluble in alcohol (35 vol.) and water (4 vol.). A convenient method of preparation is to pass hydrogen chloride into boiling methanol in the presence of zinc chloride; the evolved gas is washed with potassium hydroxide solution and dried over sulphuric acid. Methyl bromide, bromomethane m.p. --93" 7 ~ dO I "73, is used considerably as a fumigant and insecticide (T. Goodey, J. Helminthol., 1945, 2x, 45). For micromethods of determination see S. E. Lewis and K. Eccleston, J. Soc. chem. Ind., 1946, 65, 149. Methyl iodide, iodomethane, f.p. - - 6 6 . 4 ~ d o 2.35, is prepared from methyl alcohol, iodine and phosphorus or from dimethyl sulphate and potassium iodide in aqueous solution. It is a heavy, sweet-smelling liquid, forms a crystalline hydrate 2CH3I, H~O, and with methyl alcohol a compound 3CH8I, CH3OH, b.p. 4 o~ without decomposition (jr. Meunier, Bull. Soc. chim. Fr., 19Ol, [iii] 25, 572). At low temperatures, the alkyl iodides take up chlorine to form unstable iodochlorides. Methyl iodochloride, CH3IC12, m.p. N 2 8 ~ yellow crystals, decomposes into iodine monochloride and methyl chloride (J. Thiele and W. Peter, Ber., 19o5, 38, 2842) Ethyl fluoride, b.p. --37" 7 ~ f-P. --143" 2~ is formed by the addition of hydrogen fluoride to ethylene (A. v. Grosse and C. B. Linn, J. org. Chem., 1938, 3, 26) and by heating potassium fluoride with ethyl p-toluenesulphonate alone or in diethylene glycol solution (Edgell and Parts, loc. cir.). Ethyl chloride, f.p. N136" 4 ~ d o 0.923, can be prepared by a similar method to t h a t described for methyl chloride. It is an ethereal liquid, miscible with alcohol and only sparingly soluble in water; it is used as a local anaesthetic. Heated with water at IOO~ in a sealed tube it is hydrolysed to ethyl alcohol, a change catalysed by alkali. With chlorine in the presence of diffused sunlight it gives ethylidene chloride, CH3.CHC1 v and other substances; in the presence of iron as a catalyst, ethylene dichloride. Ethyl bromide, f.p. m l I 8 . 6 ~ d x5 1.47, is used as a narcotic. Ethyl iodide, f.p. m l I O - 9 ~ d o 1.98o was discovered by Gay-Lussac in 1815. It is prepared from alcohol, iodine and phosphorus; or from diethyl sulphate with potassium iodide solution (R. F. Weinland and K. Schmid, Ber., 19o5, 38, 2327; G.P., I75,2o9/I9O5). n-Propyl fluoride, b . p . - - 3 ~ f.p. --1590 can be prepared by reacting hydrogen fluoride with cyclopropane (A. V. Grosse and C. B. Linn, J. org. Chem., 1938, 3, 26) and by heating potassium fluoride with n-propyl p-toluenesulphonate in diethylene glycol solution (Edgell and Parts, loc. cit.). Isopropyt fluoride, b.p. --IO ~ f.p. m I 3 3 . 4 ~ is prepared from isopropyl fluoroformate (S. Nakanishi

488

HALOGENATED ALIPHATIC HYDROCARBONS

3

et al., J. Amer. chem. Soc., 1955, 77, 3o99) or from the p-toluenesulphonate as for n-propyl fluoride, n-Propyl bromide; f.p. --lO9-8 ~ d 15 1.3596. Isopropyl bromide, f.p. --89.o ~ d o 1.3471, is obtained from the corresponding alcohol. n-Propyl iodide, f.p. --98.7 ~ d 15 1.7584, is prepared from n-propyl alcohol. Isopropyl iodide, f.p. ~ 9 o ~ d 1~ 1.7137 is prepared from isopropyl alcohol or conveniently, by distilling a mixture of glycerol, amorphous phosphorus and iodine. ,4myl halides. See A. Michael and F. Zeidler, Ann., 191I, 385, 227. (b) Dihalogenopara~ns. Dihalogenoalkanes CnH~nX ~ (i) With two halogen atoms attached to the same carbon atom. Alkylidene halides; gem-dihalides (I) Preparation: (a)From aldehydes and ketones. (I) Using phosphorus halides: with the pentachloride usually some hydrogen chloride is eliminated and the product is a mixture of gem-dichloride and monochloro-olefin (J. L. Jacobs, Org. Reactions, 1949, 5, 20): 2RCOCH~R' + 2PC15

> RCCI~CH~R' + RCCI=CHR' + HC1 + 2POC13

Phosphorus pentabromide causes mainly ~-halogenation of ketones (A. E.

Favorski et al., J. pr. Chem., 1913, [ii], 88, 641) but it, or phosphorus trichloride dibromide, PC13Br~, is sometimes used with aldehydes (G. N. Burkhardt and W. Cocker, Rec. Tray. claim., 1931, 50, 837): CH3CHO

> CH3CHBr2

(2) Difluorides are prepared using sulphur tetrafluoride (W. R. Hasek, W. C. Smith and V. A. Engelhardt, J. Amer. chem. Soc., 196o, 82, 543): CH3(CHg.)sCHO + SF4

> CHs(CHz)5CHFg. + SOF~

CH3COCH3 - ~> CH3CF,CH3 (b) By addition of halogen acids to vinyl halides or alkynes. Vinyl bromide reacts easily with aqueous hydrobromic acid alone or in acetic acid (G. N. Burkhardt and W. Cocker, loc. cit.) or with gaseous hydrogen bromide to form ethylidene dibromide; as an alternative gaseous acetylene m a y be used (J. P. Wibaut, Rec. Trav. chim., 1931, 50, 313). Addition of hydrogen fluoride to alkynes proceeds easily, acetylene giving vinyl fluoride and I,I-difluoroethane at room temperature. Numerous catalysts have been used. When chloroalkenes react with hydrogen fluoride, hydrogen chloride is eliminated and gem-difluoroalkanes result (A. M. Lovelace et al., "Aliphatic Fluorine Compounds", Reinhold, New York, I958, pp. 13, 14, 34, lO6).

I

DIHALOGENOPARAFFINS

489

(C) By reductive elimination of halogen from trihalides. I,I,I-Tri-bromides and-iodides can be converted into the dihalogeno-compounds using sodium arsenite (W. W. Hartman and E. E. Dreger, Org. Synth., Coll. Vol. I, 1941, P. 357; R. Adams and C. S. Marvel, ibid., 358): CHI3(CHBr3) + Na3AsO3 + NaOH 8s-97%_>CHglg.(CHgBrz) + 1WaI(Br) + Na3AsO4 Hydrogen iodide will reduce I,I,2-tri-iodoethane to I,I-di-iodoethane (F.

Kri~ger and M. Ri~ckert, Chem. Ind., (Berlin), 1895, 454). (d) By halogen exchange. Alkylidene dichlorides are converted to chlorofluorides and difluorides by antimony trifluoride preferably in the presence of a pentavalent antimony salt: RCClzR'

SbF8 +SbFsCI~--> R C C 1 F R ' + 1RCFol~'

Much less attention has been paid to bromides which tend to undergo side reactions" CH~BrCHBr9

SbFa + Br~- -,~ C H ~ B r C H F B r + C H ~ B r C H F 9 ~oo0

(A. M. Lovelace et al., loc. cit., p. 7). Alternatively, hydrogen fluoride may be used either with or without a catalyst (Lovelace et al., loc. cit., p. 15; F. Cuthbertson and W. K. R. Musgrave, J. appl. Chem., 1957, 7, 99): CH3CHC19" HF, SnCl, __> CHaCHC1F + CHaCHF~. Mercuric fluoride has also been used (A. C. Henne and M. W. Renoll, J. Amer. chem. Soc., 1936, 58, 889)" CH3CHBr~" HgF~ ~ CHaCHBrF + CHaCHFz Chlorine in methylene chloride can be replaced by iodine by heating with sodium iodide in acetone solution (W. H. Perkin, Jr., and M. A. Scarborough, J. chem. Soc., 1921, 14oo ). (2) Prolberties and reactions. Gem-dihalides show a sharp decrease in the reactivity of the carbon-halogen bond compared with the alkyl halides, which they resemble in their main reactions. On heating at 350-45 o~ ethylidene chloride breaks down into hydrogen chloride and vinyl chloride (D. H. R. Barton, J. chem. Soc., 1949, 148)" at

49 ~

HALOGENATED ALIPHATIC HYDROCARBONS

3

2oo-3oo ~ the bromide isomerises (A. Favorsky et al., Ann., I9O7, 354, 325) giving an equilibrium mixture containing ethylene dibromide along with some ethyl bromide and tribromoethane formed as by-products. The gem-dihalides can be hydrolysed by water or by warming with sodium acetate in acetic acid" RCBrzR' + H20-~ RCOR' + 2HBr

(C. S. Marvel and W. M. Sperry, Org. Synth. Coll. Vol. I, 1941, p. 5; L. A. Bigelow and R. S. Hanslick, ibid., II, 1943, 244; G. Wittig and F. Vidal, Ber., 1948, 8I, 368). They are relatively resistant towards alkali, especially the difluorides, which remain unhydrolysed with aqueous alkalis (G. N. Burkhardt and W. Cocker, Rec. Trav. chim., 193I, 5o, 843). Dehydrohalogenation occurs with a variety of reagents, e.g. sodamide (R. Les2hieau and M. Bourgei, 0rg. Synth. Coll. Vol. I, 1941, p. 191; Bourgel, Ann. chim., 1925, [IO], 3, 191,325), caustic potash in mineral oil (G. B. Backman and A. J. Hill, J. Amer. chem. Soc., 1934, 56, 2730; H. H. Guest, ibid., 1928, 5o, I746), and molten caustic potash (J. C. Hessler, Org. Synth. Coll. Vol. I, 1941, p. 438), to give alkynes (see also T. L. Jacobs, 0rg. Reactions, 1949, 5, I). Methylene fluoride, difluoromahane, CH2F s, b.p. m51.6~ is formed from methylene chloride and silver fluoride or by the reduction of chlorofluoroform, CHC1Fz (A. F. Benning and E. G. Young, U.S.P., 2,615,926/I952 ). Methylene chloride, dichloromethane, m.p. m96.8~ b.p. 4o.o ~ d~s 1.33 is prepared by chlorinating methyl chloride (I.G., B.P., 489,554/1938); by the reduction of chloroform with zinc and acetic acid (R. L. Bacl~rach, C.A., 1935, 29, 3113) or from trioxymethylene and phosphorus trichloride. Methylene bromide, m.p. w 5 2 . 7 ~ b.p. 97.o ~ di~ 2.50, results from the reduction of bromoform with sodium arsenite (W. W. Hartman and E. E. Dreger, Org. Synth., Coll. Vol. I, P. 357), the bromination oi methyl bromide, or the action of phosphorus pentabromide on trioxymethylene. Methylene iodide, m.p. 6.o ~ b.p. 66-7o/II ram., d~ 3"33, by reduction of iodoform with sodium arsenite or hydrogen iodide. Ethylidene fluoride, I,I-difluoroethc~ne, CHaCHF 2, b.p. m24 97 ~ is formed when hydrogen fluoride is added to acetylene in the presence of catalysts (J. D. Cal/ee andF. H. Bratlon, U.S.P., 2,462,359/1949; A. yon Grosse and C. B. Linn, J. Amer. chem. Soc., 1942, 64, 2289) or by the action of sulphur tetrafluoride on acetaldehyde. Ethylidene chloride, I,I-dicMoroahane, m.p. --96-6 ~ b.p. 57" 3~ d~5 I. I8,' is manufactured by addition of hydrogen chloride to vinyl chloride in the presence of aluminium chloride (Consortium liar electrochem. Ind., F.P., 8oi,49o/I936; B.P., 454,I28/I936). It may also be obtained by treatment of acetaldehyde with phosphorus pentachloride. Ethylidene bromide, b.p. II2.5~ mm., d~ 2-IO, is obtained by the addition of hydrogen bromide to vinyl bromide or by reaction of acetaldehyde with phosphorus trichloride dibromide. Ethylidene iodide, b.p. I77-9 ~ d o 2-84, is produced by the reduction of I,I,2-tri-iodoethane with

I

DIHALOGENOPARAFFINS

491

hydrogen iodide or by addition of the latter to acetylene IF. Kri~ger and M. Pi~ckert, Chem. Ind. (Berlin), 1895, 454]2,2-Difluoropropane CH3CFzCH 3, b.p.---o-6 ~ d o 0"92; I,I-dichloropropane, CH3CH,CHClz,, b.p. 85-87 ~ d 1~ I- 14 92,2-dichloropropane, b.p. 69" 7~ *r I. 4o93, d *~I "093" 2,2-difluorobutane, CH3CFzCHgCH 3, b.p. 30" 8~ n~ I. 3182, d 1~o'9164" 2,2-dibromobutane, b.p. 144-5~ 2,2-dichloro-3,3-dimethylbutane, CH3CC19C(CH3)3, m.p. 1510 (produced from pinacone and phosphorus pentachloride, M. Delacre, Bull. Soc. chim. Fr., 19o6, [iii], 35, 343).

(ii) With the two halogens attached to digerent carbon atoms. A lkylene dihalides. (I) Preparation. (a) By the addition of halogens to olefins. Addition occurs at the double bond in the trans configuration (H. J. Lucas and C. W. Gould, J. Amer. chem. Soc., 1941, 63, 2541). Addition of chlorine is carried out slowly at a low temperature to limit substitution (E. F. Degering, Ind. Eng. Chem., 1932, 24, 181; H. J. Lucas, T. P. Simpson and J. M. Carter, J. Amer. chem. Soc., 1925, 47, 1462). Sulptluryl chloride (cf. M. S. Kharasch and H. C. Brown, ibid., 1939, 6i, RR'C=CR'R"

+ SO~C19

~ R R ' C C 1 - - C C I " R ~ R " + SO S

3432; A. Mooradian and J. B. Cloke, ibid., 1946, 68, 785), phosphorus pentachloride (cf. L. SpiegIer and J. M. Tinker, ibid., 1939, 6I, 940; D. P. Wyman, J. Y. L. Young and W. R. Freeman, J. org. Chem., 1963, 28, 3173 ), or tetrabutylammonium tetrachloroiodate (R. E. Buckles and D. F. Knaack, ibid., 196o, 25, 20) can be used. Dibromides are more convenient to prepare, since the reaction is less vigorous. The olefin is usually passed into bromine covered with a layer of water or is added to a solution of bromine in carbon tetrachloride, chloroform, carbon disulphide, acetic acid or ether (cf. for typical examples, J. R. Johnson and W. L. McEwen, Org. Synth. Coll. Vol. I, 1941, p. 521; C. G. Schmitt and C. E. Boord, J. Amer. chem. Soc., 1932, 54, 75i; F. J. Soday and Boord, ibid., 1933, 55, 3293). The bromine can also be used in the form of a stable perbromide of a quaternary base e.g. pyridinium bromide perbromide (C. Djerassi and C. R. Scholz, ibid., 1948, 70, 417). Bromine and chlorine can be added to olefins simultaneously by using hydrogen chloride and N-bromoacetamide (Buckles and J. W. Long, ibid., 1951, 73, 998) 9 Iodine and chlorine can be added simultaneously to give iodochlorides by using mercuric chloride and iodine (S. Winstein and A. Grunwald, ibid., 1948, 7o, 836). Iodine monochloride will also add normally to give the same products (H. Ingle, J. Soc. chem. Ind., 19o2, 2i, 587). In the form of Wijs'

492

H A L O G E N A T E D A L I P H A T I C HYDROCARBONS

3

reagent this is used to determine the extent of unsaturation in organic compounds (A. I. Vogel, "Elementary Practical Organic Chemistry", Part 3, Quant. Org. Analysis, Longrnans, London, I958, p. 756). Iodine has much less tendency than the other halogens to add to double bonds. It has been claimed that fluorine can be added to the double bonds of hydrocarbons by treating them with lead tetrafluoride (0. Dimroth and W. Bockemi~ller, Ber., 1931, 64, 516): PhgC =CHg. ---+ PhzCF-- CHeF

but other workers have been unable to repeat this reaction and have pI epared the reagent in situ from lead peroxide and hydrogen fluoride. This will add fluorine across the double bonds of chlorinated and fluorinated olefins but no examples using simple olefinic hydrocarbons are given (A. L. Henne and T. P. Waalkes, J. Amer. chem. Soc., 1945, 67, 1639). (b) From glycols and halogenohydrins. Dihydric alcohols will react with phosphorus halides and hydrogen halides to give the corresponding dihalides. If halogenohydrins are used, mixed dihalogeno-compounds may be produced (J. B. Cloke et al., J. Amer. chem. Soc., 1931, 53, 2794; D. Starr and R. M. Hixon, ibid., 1934, 56, 1595; J. D. Bartelson, R. E. Burk and H. P. Lankelma, ibid., 1946, 68, 2513; 0. Kamm and C. S. Marvell, Org. Synth. Coll. Vol. I, 1941, p. 25). 1,2-Glycols react satisfactorily with hydrogen bromide in acetic acid in presence of sulphuric acid (D. E. Ames, J. chem. Soc., 1951, lO19). Thionyl chloride can also be used in the presence of pyridine (K. Ahmad, F. M. Bumpus and F. M. Strong, J. Amer. chem. Soc., 1948, 70, 3391): SOCls

CHgOH(CH2)~CH~OH c, HsN-+ CI(CH~)~C1 + HC1 + SO9.

Di-iodides are pIoduced when potassium iodide and 95 ~/o orthophosphoric acid are used (H. Stone and H. Shechter, J. org. Chem., 195o, 15, 491) : KI HOCH~(CH~)4CHg.OH HsPO.'-+ ICHz(CHz)4CHzI

(c) From esters. Di-iodides can be prepal ed from the di-toluenesulphonates and sodium iodide in acetone solution (R. S. Tilhson, M. A. Clalbp and C. H. Critcher, ibid., 1947, I2, I33 ), while mixed chloroiodides are obtained from chloroalkanesulphonates, and chlorofluorides and bromofluorides from chloro and bromo-alkanesulphonatcs and potassium fluoride in diethylene glycol (F. L. M. Pattison and J. E. Millington, Can. J. Chem., 1956, 34, 757). (d) By halogen exchange. Bromides are converted into chlorides or bromochlorides by heavy metal chlorides (C. W. Li~ssner, J. pr. Chem., I876, 13, 421) : CHgBrCH2Br

> CHgBrCH2C1

> CHgC1CH~C1

I

DIHALOGEN OPARAFFINS

493

Dibromides and dichlorides or mixed dihalides will react with sodium iodide in acetone solution to give iodohalides and di-iodides (K. Ahmad et al., l~c. cit., p. 1699, 3391; H. B. Hass and H. C. Hugman, J. Amer. chem. Soc., 1941, 63, 1233). Both bromine and iodine have been replaced by fluorine using mercuric fluoride but yields are low (A.L. Henne and M.W. Renoll, ibid., 1936, 58, 889) :

CH~I(Br) HgF2+ CH2F

I

CH~I(Br)

I

CHgF

+l

CH~I(Br) CHeF

A better method is to heat the dichloride or dibromide with potassium fluoride in ethylene glycol solution when either the mixed dihalide or the difluoride is obtained. Ethylene difluoride cannot be prepared in this way (F. W. Hogmann, J. org. Chem., 1949, I4, IO5: 195o, 15, 425) 9 (e) By the action of bro~nin~ or iodine on the silver salt of a dibasic acid (C. V. Wilson, Org. Reactions, 1957, 9, 332):

AgOgC(CHg.)nCO2Ag Br~__~Br(CH~)nBr

(f) From tertiary alcohols and halogens, which give 1,2-dihalogeno-compounds (F. C. Whitmore et al., Org. Synth., Coll. Vol. II, I943, p. 408): (CH3)~C(OH)C2H5 Br,_+ (CH3)zCBrCHBrCH3 (g) The cleavage of heterocyclic rings by acidic reagents. Tetrahydrofuran reacts with hydrogen chloride to give a chlorohydrin (D. Starr and R. M. Hixon, Org. Synth. Coll. Vol. II, 1943, p. 571) which with phosphorus tribromide gives the bromochloride:

CHgmCH~ I I HCl PBr,+ CH~ CH~ ~ HO(CHg.)IC1 Br(CHz),C1 In the presence of zinc chloride hydrogen chloride gives 1,4-dichlorobutane (S. Freed and R. D. Kleene, J. Amer. chem. Soc., 1941, 63, 2691). Hydrogen bromide alone gives the dibromide (Idem, ibid., 194o, 62, 3258). Tetrahydropyrans react similarly (M. Piantanida, J. pr. Chem., 1939, 153, 257; Org. Synth. Coll. Vol. III, p. 692 ), or phosphorus and bromine can be used (J. B. Cloke and O. Ayers, J. Amer. chem. Soc., 1934, 56, 2144). The di-iodide is obtained using potassium iodide and phosphoric acid (H. Stone and H. Shechter, J. org. Chem., 195o, 15, 491). N-benzoylpyrrolidine and N-benzoylpiperidine give 1,4 dibromobutane

494

HALOGENATED ALIPHATIC HYDROCARBONS

3

and 1,5-dibromopentane with phosphorus pentabromide (J. yon Braun, Org. Synth. Coll. Vol. I, 1941, p. 428; N. J. Leonard and Z. W. Wicks, J. Amer. chem. Soc., 1946, 68, 2402 ). (h) From alkylenediamines. Nitrosyl chloride or bromide and diamines (W. A. Solo~ina, J. Soc. phys.-chem, russe, 1898, 3o, 6o6), or their acyl derivatives with phosphorus pemtachloride or pentabromide also give dihalides (J. yon Braun and E. Damiger, Ber., 1912, 45, 197o; G. C. H. Stone, J. Amer. chem. Soc., 1936, 58, 488). (i) Free radical chlorination of alkyl chlorides using sulphuryl chloride and benzoyl peroxide gives isomeric mixtures of the possible dichlorides (M. S. Kharasch and H. C. Brown, J. Amer. chem. Soc., 193 9, 6I, 2142; idem and T. H. Chao, ibid., 194o, 62, 3435)" CHsCH~CH2C1

~> CHaCHC1CHgC1+ CH2C1CH2CHg.C1

(2) Properties and reactions. The dichloro- and dibromo-alkanes are stable and provide a range of valuable solvents. At about 40o o ethylene dichloride undergoes pyrolysis to hydrogen chloride and vinyl chloride by a first order chain mechanism which is inhibited by propene (D. H. R. Barton and K. E. Howlet, J. chem. Soc., 1949, 148, 155). Tile stabilities of the difluorides, chlorofluorides, bromofluorides, dichlorides and dibromides to nucleophilic reagents have been compared and the fluorine atoms shown to be less reactive than any of tile other halogens (F. W. Hoffmann, J. olg. Chem., I949, 14, lO5; I95o, 15, 425). 1,2-Di-iodides lose iodine on heating with potassium iodide at moderate temperatures; this property enables the preparation of unsaturated compounds from glycols (C. S. Hudson et al., J. Amer. chem. Soc., 1944, 66, 73; P. L. Julian et al., ibid., 1945, 67, 1728; B. Helferich, Adv. Carbohydrate Chem., 1948, 3, 98). meso-I,2-Dibromides are more quickly dehalogenated by potassium iodide to trans-olefins; I)Ldibromides on the other hand give (more slowly) cis-isomers (W. G. Young et al., J. Amer. chem. Soc., 1939, 6x, 164o, 1645). The most common method of dehalogenation of vicinal dihalides is by zinc dust in solvents like alcohol, dioxan, acetic anhydride, acetic acid or dimethylformamide. Tile process of halogenation followed by dehalogenation is often used to purify olefins. These reagents will eliminate chlorine (L. Schmerling, ibid., 1945, 67, I438), bromine (F. J. Soday and C. E. Boord, ibid., 1933, 55, 3293), bromine and fluorine, and iodine and fluorine (.4. Bowers et al., ibid., 196o, 82, 4OOl) but not fluorine alone, meso-I,2-Dibromobutane with zinc gives trans-but-2-ene, the cis-olefin is formed from the DL-isomer (H. O. House and R. S. Ro, ibid., 1958, 8o, 182). With ethylene dichloride sodium in liquid ammonia produces ethylene directly (E. Chablay, Compt. rend., 19o6, x42, 94). An isolated halogen atom is often unaffected unless there are two such halogen atoms so situated that ring for-

I

DIHALO GEN OPARAFFIN S

495

marion or coupling can occur (C. L. Wilson, J. chem. Soc., 1945, 50). In this way cycloalkanes are prepared generally from ~, oj-dibromoalkanes but some dichlorocompounds can be used (H. B. Hass et al., Ind.]Eng. Chem., 1936, 28, 1178). I t must also be remembered, however, (see p. 486) that iodine and sometimes bromine can be replaced by hydrogen using zinc and acetic acid or ethyl alcohol. Alkyl-lithiums can also eliminate the halogen atoms from vicinal dihalides (G. Wittig and G. Harborth, Ber., I944, 77, 3o6). The poly-methylene dibromides Br(CH2)nBr where n > 3 will form diGrignard reagents and di-lithium compounds. Their preparation and uses have been reviewed (I. T. Millar and H. Heaney, Quart. Reviews, I957, ix, lO9). The bromofluorides form only mono-Grignard reagents (W. C. Howell et al., J. org. Chem., 1957, 22, 255). When the two halogen atoms are a t t a c h e d to different carbon atoms, ~udeophilic reagents react primarily in the same way as with alkyl halides but this initial reaction is often followed by further processes consequential on the presence of two reactive groupings in the molecule. Aqueous alkali with a 1,2-dihalide produces a glycol (0. J. Schierholtz and M. L. Staples, J. Amer. chem. Soc., 1935, 57, 271o) but the latter are usually prepared via the diesters by heating the dihalides with sodium acetate in acetic acid or alcohol (L. Gattermann, "Laboratory Methods of Org. Chem.", Macmillan, London, 1938, 115). Alcoholic alkali, caustic potash in mineral oil, or molten caustic potash, carx give halogeno-olefins : CHsCHBrCHBrCH 8 - - + CH3CBr

-

-

CHCH8

(j. Wislicenus et al., Ann., 19oo, 313, 237), acetylenes (I. M. Heilbron et al., J. chem. Soc., 1946, 27; L. Pauling et al., J. Amer. chem. Soc., 1939, 61, 927), or di-olefins (K. yon Auwers, Ber., 1918, 5z, II26): RR'CXCH(CHs)X

> RR'C=C=CH~

Olefinic ethers can also be formed (I.G., B.P., 34I,O74/I929) : RCHXCH2X

> RCH=CHX ~

RCH=CHOR'

Sodamide will also give acetylenes (T. L. Jacobs, Org. Reactions, 1949, 5, i). Heterocyclic compounds are formed from 1,2-, 1,3-, 1,4- and 1,5-dihalides and alkali, sulphides, ammonia or amines under mild conditions: CH~--CH~ Br(CHgJ4Br

N~.s

I

I

> CH~ CHI ~S j

(D. E. Wol[ and K. FoIkers, Org. Reactions, 1951, 6, 4IO).

496

HALOGENATED ALIPHATIC HYDROCARBONS

3

CHzmCHg. Br(CH,)/Br

PhNH,_+ CH, [ ] CH, Ph

(j. yon Braun and G. Lemke, Ber., 1922, 55, 3556). With a tertiary amine a quaternary salt is formed if one halogen atom is much less reactive than the other: FCH~CH,Br + NMe3 ---+ FCH2CHzN*Me3Bre (B. C. Saunders, J. chem. Soc., 1949, 12791. With sodium cyanide the dihalides give halogenonitriles (C. F. H. Allen, Org. Synth. Coll. Vol. I, 1941, p. 156; C. S. Marvel and E. M. McColm, ibid., p. 536) and eventually dinitriles, e.g. adiponitrile from 1,4-dichlorobutane, N. B. Copelin and F. J. Feldhousen Jr., U.S.P., 2,783,268/I957). Sodio-derivatives of acetoacetic ester, malonic ester and fl-diketones have been used extensively, with dibromides, to produce cycloalkane acids and cycloalkanes (F. H. Case, J. Amer. chem. Soc., 1933, 55, 2927; 1934, 56, 715). The bromofluorides react to give fluoroalkyl derivatives only e.g. /COCH3 F(CH,)nCH ~C09Et

(F. W. HoGmann, J. org. Chem., 195o, 15, 425). Inorganic sulphides react with dihalides on heating to give polymeric sulphides which are rubber-like elastomers resistant to many solvents (Thiokol, Vulcaplas, see Dict. appl. Chem., Io, 631) but the lower reactivity of fluorine restricts the process when it is present (B. C. Saunders et al., J. chem. Soc., 1949, 916): FCHg.CH~Br + NaSH

~ FCH~CH2SH

2FCHgCH2SNa + FCHgCH~Br

NaOH

> FCH~CH~SNa

~ FCHgCH2SCH~CH2SCHgCH2F

Hydrogenation of dihalides over palladised calcium carbonate proceeds through the alkyl halides to the alkane. Lithium aluminium hydride causes some olefin formation (J. E. Johnson et al., J. Amer. chem. Soc., 1948, 7o, 3664; L. W. Trevoy and W. G. Brown, ibid., 1949, 71, 1675). For reduction of dihalides in alkaline solution see R. Stoermer, in Houben-Weyl, "Die Methoden der Organischen Chemie", Leipzig, 1925, 363. W h e n heated to temperatures of 200-300 ~ isomerisation of dibromides occurs to give equilibrium mixtures of isomerides. At higher temperatures the m i x t u r e also contains mono- and tri-bromides (A. Faworsky et at., Ann., 19o7, 354, 325).

I

D I HALOG E N O P ARAF FIN S

497

For reviews on the mechanism and stereochemistry of substitution and elimination reactions of dihalides and of halogenohydrins and their esters, see E. A. Braude, Ann. Reports, 1949, 46, 122; A. Streitwieser, Chem. Reviews, 1956, 56, 571; H. O. House and R. S. Ro, J. Amer. chem. Soc., 1958, 8o, 182. The physical properties and methods of ultimate purification of representative alkylene dihalides are recorded by D. H. R. Barton and K. E. Howlett (J. chem. Soc., 1949, 155) and C P. Smyth et al. (J. Amer. chem. Soc., 195o, 72, 2o71). Ethylene difluoride, 1,2-difluoroethane, FCH~CH2F, b.p. 30.7 ~ obtained by treating ethylene dibromide with mercuric fluoride (A. L. Henne and M. W. Renoll, J. Amer. chem. Soc., 1936, 58, 890; 1938, 60, IO6O), may be stored as a gas but decomposes slowly as liquid (W. F. EdgeU and L. Parts, ibid., 1955, 77, 4899). Ethylene dichloride, 1,2-dichloroethane, C1CH~CH~C1, b.p. 83.4 ~ f.p. - - 3 5 . 9 ~ d~~ 1.25288, n ~ 1.445o, can be prepared by any of the methods described. The addition of chlorine to ethylene, though used commercially, is satisfactory only below o ~ because at higher temperatures substitution occurs (see E. H. Huntress, "Organic Chlorine Compounds", Wiley, New York, 1948, P- 594)- Ethylene dibromide, b.p. 131.41~ m.p. IO~ d~~ 2.179, is formed when ethylene is passed into a mixture of bromine and water. Ethylene diiodide, m.p. 83 ~ d x~ 2" 132, is best prepared by saturating a mixture of iodine and anhydrous ethanol with ethylene. It loses iodine on keeping (T. S. Patterson and J. Robertson, J. chem. Soc., 1924, 125, 1526; T. Iredale and T. R. Stephan, J. phys. Chem., 1945, 49, 595)The 1,2-dihalogenopropanes result from the addition of halogens to propene, and of halogen hydrides to allyl halides. Propylene dichloride, 1,2-dichloropropane, CH3CHC1CH2C1, b.p. 96.2 ~ d~~ 1.1574, n ~ 1-439o. 1,2-Dibromopropane, b.p. i42~ d~~ 1.9405, n ~ i . 5 2 o 9 (M. S. Kharasch et al., J. Amer. chem. Soc., 1935, 57, 2463). Trimethylene dihalides, 1,3-dihalogenopropanes, are obtained by peroxidecatalysed additions to allyl halides. Trimethylene dibromide is formed in the cleavage of cyclopropane with bromine. The rupture of the ring is more rapid if other alkylsubstituents are present. The cyclopropane ring, when unsymmetrically substituted, breaks between the carbon atoms holding the largest and smallest number of alkyl groups (E. P. Kohler and J. B. Conant, ibid., 1917, 39, 1404)For physical constants, see H. Serwy, Bull. Soc. chim. Belg., 1933, 42, 485 9 1,3-Difluoropropane, FCH~CH~CH~F, b.p. 41.6, d~5 1.oo57; 1,3-dichloropropane, b.p. 12o ~ d~~ 1.1878, n ~ 1.4487" 1,3-dibromopropane, b.p. 167-3 ~ d~~ 1.9822, n ~ 1.5233" 1,3-diiodopropane, b.p. IIO~ ram., d~ 2"5755, n ~ 1.6423. (For a review of a, oj-difluoroalkanes see F. W. Hoffmann, J. org. Chem., 1949, 14, lO5). 1,4-Difluorobutane, b.p. 77.8 ~ d~5 0.9767. Dichlorobutanes occur with I-chlorobutane-4-sulphonyl chloride, when chlorine and sulphur dioxide are passed into irradiated n-butyl chloride (J. H. Helberger et al., Ann., 1949, 562, 23): 1,2-Dichlorobutane, b.p. I24 ~ d~~ 1.118, n~ 1.4474" 1,3-dicMorobutane, b.p. ram., d~~ 133.5 ~ d~~ 1.1191, n ~ 1.4445, and 1,4-dichlorobutane, b.p. 155~ I. 1598, n "~ 1.4566, are formed in the photochemical chlorination of butyl chloride, meso-2,3-Dichlorobutane, b.p. 115.9~ mm., d~5 1.1o25, n~5 1-4386"

498

HALOGENATED ALIPHATIC HYDROCARBONS

3

DL-/orm, b.p. 119" 5~ ram., d2r2 I. lO63, n~)5 1-44o9, the (--)-isomer has also been obtained (H. J. Lucas and C. W. Gould, J. Amer. chem. Soc., 1941, 63, 2541). 1,2-Dibromobutane, b.p. 55~ ram., d~~ 1.7951, n~)~ 1.5144; 1,3-dibromobutane, b.p. 175~ mm." 1,4-dibromobutane, b.p. 198~ mm., d~~ i. 8080, n~)~ I. 5191. 1,4-Diiodobutane, b.p. I25-I27~ mm., f.p. 6 ~ d~6 2.349, n{)5 1.619. Dihalogenopentanes: 1,5-difluoro-, b.p. lO5-5 ~ d~5 o'9572; 1,2-dichloro-, b.p. mm., n~)~ 1.4485" 1,4148.4_148.8 o, ~r 1.4485. 1,3-dichloro-, b.p. 8o.4~ dichloro-, b.p. 88.1~ mm., n~)~ 1.45o 3" 1,5-dichloro-, b.p. 182.3~ mm., n~)~ 1.4563; 2,3-dichloro-, exists in two forms b.p. I4O-I4 I~ n{)~ 1.4468 and mm. (mixed stereob.p. 143-144 ~ n~)~ 1.4476" 2,4-dichloro- , b.p. 142-147~ isomers); 1,2-dibromo-, b.p. 85~ o mm., n~)~ 1.5o63; 1,3-dibromo-, b.p. 73-75~ mm., n~)5 1.51o5; 1,5-dibromo-, 14 mm., n~)5 1.5o9; 1,4-dibromo- , b.p. 94-96~ b.p. IO6-9-IO7-4o/24 mm., n~)~ 1.5136; 2,3-dibromo-, f.p. m56.o~ , b.p. 91 ~ 50 mm., ~r 1.5o96 (+-erythro-isomer) and f.p. m 3 3 ~ b.p. 92.4~ o ram., n~)~ 1.5o96 (i-threo-isomer); 2,4-dibromo-, b.p. 75~ mm., 1,3-diiodo-, b.p. 80-82~ mm.; 1,4-diiodo-, b.p. lOO~ mm., 1,5-diiodo-pentane, b.p. lO9I I I ~ mm. Dihalogeno-2-methylbutanes: 1,2-dichloro-, CH3CHzCCI(CH3)CHzC1, b.p. 71- 5o/ mm., (--)-isomer, IOO ram., n ~ "5 1.4432; 1,3-dichloro-(+)-isomer, b.p. 91~ b.p. 89.2~ mm.; 1,4-dichloro- (+)-/orm, b.p. I7O-I72~ (--)-isomer, b.p. mm., n~)~ 1.5o88" lO1-1o2 ~ n~J 1.4562, [ x ] ~ - - 9 . 7 ~ 1,2-dibromo-, b.p. 6o-62~ 1,4-dibromo-, b.p. 125-128~ mm.; 2,3-dibromo-, f.p. I 4 - I 6 ~ b.p. 54--56~ 14 ram., n~)~ 1-5o9o- 3,4-dibromo-, b.p. 65-66~ mm. 1,6-Difluorohexane, b.p. I29.9 ~ d~5 0.94o7 . 1,6-Dichlorohexane, b.p. 99~ ram., n~)5 I. 458 (R. A. Raphael and F. Sondheimer, J. chem. Soc., 195 o, 2IOO), and 1,9-dichlorononane, b.p. 9o-92~ 9I mm., n ~ 1-459 (K. Ahmad et al. J. Amer. chem. Soc., 1948, 7o, 3392) are prepared from the glycol with thionyl chloride and a base. The following are prepared with hydrogen bromide: 1,6dibromohexane, b.p. 12o~ ram., n~)5 1.511; 1,9-dibromononane, b.p. 128-13o~ 2 mm., d 15 1.415; I,Io-dibromodecane, m.p. 28 ~ b.p. 139-142~ mm., n~)5 1.493. 2,5-Dibromohexane, meso-form, m.p. 39 ~ b.p. 99~ mm.; DL-form, b.p. 94o/ 14 mm. (N. Kornblum and J. H. Eicher, ibid., 1949, 7x, 2259). Trimethytethylene dibromide, 1,2-dibromo-2-methylbutane, (CH3) ~CBrCHBrCH 3, b.p. 490_510/ I i mm., prepared from tert-amyl alcohol, by bromination (Org. Synth., Coll. Vol. I, 2nd. Edition, 1948, p. 30 et seq.) produces an allene Oil dehydrohalogenation; in hydrolytic conditions it is converted to 3-methylbutan-2-one. 2-Bromo-I-chloroethane, b.p. lO6.6-1o6.7 ~ d~~ 1.7392, n ~ 1.4917, is prepared from vinyl chloride and hydrogen bromide in presence of peroxide; I-chloro2-iodoethane, b.p. i4 o~ do~5 2.134; I-chloro-2-fluoroethane, C1CHzCH,F, b.p. 5253 ~ d~~ 1-175, n~s 1.378 (H. McCombie and B. C. Saunders, Nature, 1946, x58, 382); I-bromo-2-fluoroethane, b.p. 71-5 ~ n ~ 1.423; I-fluoro-2-iodoethane, b.p. 98-1o2 ~ (For a review of a,co-fluorohalogenoalkanes see F. W. Hoffmann, J. org. Chem., 195o, I5, 425; F. L. M. Patt ison and J. E. Millington, Can. J. Chem., 1956, 34, 757). I-Bromo-2-chloropropane, CH3CHC1CHzBr, b.p. 52o/75 mm.; 2-bromoI-chloropropane, CH3CHBrCH~C1 , b.p. 52o/75 ram. (M. S. Kharasch et al., J. org.

I

T R I H A L O GE N O P A R A F F I N S

499

Chem., I937, 2, 288; 1945, 1o, 159); 3-bromo-I-chloropropane, CI(CH2)3Br, b.p. 14o-143 o (Org. Synth.). I-Bromo-4-chlorobutane, Br(CH~)4C1 , b.p. 8o-82~ o ram., and I-bromo-5-chloropentane, Br(CH2)sC1, b.p. 92-93~ ram. (M. S. Newman a n d J. H. Wotiz, J. Amer. chem. Soc., 1949, 71, 1292). I-Chtoro-6-iodohexane CI(CH~)6I, b.p. 74~ ram., n~* 1.525 (R. A. Raphael a n d F. Sondheimer, J. chem. Soc., 195o, 21o2). F o r t h e p r e p a r a t i o n of o t h e r m i x e d halides, see F. M. Strong et al., J. Amer. chem. Soc., 1948, 7o, 1699, 3391. C o m p o u n d s of the s t r u c t u r e I(CH~CH2)nCH~C1 arise from t h e free r a d i c a l - i n i t i a t e d reaction of e t h y l e n e w i t h c h l o r o - i o d o m e t h a n e (J. Harmon et al., ibid., 195o, 72, 2214).

(c) Trihalogenolbara~ns. Trihalogenoalkanes, CnH~.n_IX8 The best known representatives are the haloforms with the formulae CHX3 ( X = F , C1, Br or I).

(i) Preparation (I) By halogenation and subsequent alkaline hydrolysis of compounds possessing the acetyl group CH3.C~ O or a structure capable of producing it on oxidation" CHaCH2OH ~

CH3CHO ---+ CC13CHO - - ~ CHC13 + HCOaH PhCOCF a

aq.

alkali

> PhCO~H + HCF a

(j. H. Simons and E. O. Ramler, J. Amer. chem. Soc., 1943, 65, 389). Details for the preparation of chloroform, bromoform and iodoform usually from acetone or alcohol and alkaline hypohalite solutions, are given in most elementary practical chemistry books. (2) By the free radical addition of chloroform to olefins (M. S. Kharasch et al., ibid., 1947, 69, ILOO): (PhCO2)9.

> 2Ph. + 2CO~; Ph- + HCC18

v P h i l + .CC1a

RCH =CH~ + 9CC1a - ~ RCH--CHgCC1 a RCH--CHzCC1 a + HCC13

-~ RCHgCHgCC18 + "CC1a

If excess chloroform is used straightforward addition occurs but if the mole proportion of chloroform is reduced, telomerisation occurs because the radical initially formed attacks the olefin giving a sories of products with trichloromethyl end groups.

500

HALOGENATED ALIPHATIC HYDROCARBONS HzC =CHg. + 9CC18

~ 9CH~CHgCC13

9CH~mCHgCC13 + nCHgmCHg.---+ -CHg~CH~--(CHgmCH~)a--CCla 9CH~--CH~(CHg.--CHg.)n--CC18 + HCC13---+ CH3CHg--(CH~--CHg)nCC13 + "CC18

Similar reactions occur with bromoform and other halides but when bromine or iodine is present it is the C--Br or C--I bond which breaks to give the free radical (J. Harmon, U.S.P., 2,423,497/1947); J. Amer. chem. Soc., 195o, 72, 2213). (3) By the action of sulphur tetrafluoride on carboxylic acids (W. R. Hasek, W. C. Smith and V. A. Engelhardt, ibid., I96O, 82, 543): CH3(CH2)nCOgH + 2SF 4

> CH3(CHg.)nCF3 + 2SOF 2 + H F

(4) By the action of hydrogen fluoride on chloro-olefins containing the structure >C=CCI~ three products are formed >CHuCC12F, >CH---CC1F2 and > C H - - C F 3 (A. M. Lovelace et al., "Aliphatic Fluorine Compounds", Reinhold, New York, 1958, p. 13): > (CH3)gCHCHg.CFC1z + (CH3)~.CHCH~CF~C1 +

(CH3)~CHCH=CC1, + H F

(CHs)~CHCHzCF3

(5) By halogen exchange: CHC18 + A1Br3----+ CHBr 3 + A1C13 CHI3 + CHC13 AgF__>CHF3

(M. Meslans, Compt. rend., 189o, IiO, 717); CHC13 + SbCls + H F ( e x c e s s ) Ipress. 3 ~ 1 7 6 CHF3

(W. B. Whalley, J. Soc. chem. Ind., 1947, 66, 427); RCC13 + SbF 3 SbFsC1-------2s-+RCC1F~ + RCC12F + RCF 3

(A. L. Henne, Org. Reactions, 1944, 2, 49). (ii) Properties and reactions Those containing only chlorine, bromine, iodine or with only one fluorine atom in the trihalomethyl group react with nucleophilic reagents as does chloroform (R. N. Haszeldine, J. chem. Soc., 1952, 4260):

I

TRII-IALOGENOPARAFFINS RCCIa

aq. alkali

501

" > RCO2H

Chloroform reacts with sodium ettloxide to give ethyl orthoformate, HC(OEt)a, but when there is an alkyl group attached to the trihalogenomethyl group the possibility of elimination of hydrogen halide arises when either aqueous or anhydrous alkali is used (I.G., G.P., 429,6o4/1929)" CHaCCIa

Ca(OH),

-> CH, =CCI~

When there are two fluorine atoms present the compounds are much less reactive but will still undergo dehydrohalogenation by alcoholic caustic potash (P. Tarrant et al., J. Amer. chem. Soc., I954, 76, 2343): CH3CHCHg.CC1Fa

I CH a

> CHaCHCH=CF 2

! CH 3

Dehydrohalogenation can also be accomplished by pyrolysis (C. F. Feasly and W. A. Stover, U.S.P., 2,627,529/I953), CHsCF,C1 ~

CH,=CF, + CHg=CFC1

a process which can also lead to the formation of new carbon to carbon bonds: CHC1Fg. 7000> CFz=CF, + 2HC1

(j. D. Park et al., Ind. Eng. Chem., 1947, 39, 354). The chlorofluoro-compounds undergo disproportionation in the presence of aluminium trichloride (W. S. Murray, U.S.P., 2,426,638/1947): CHF2C1 or CHFCli AlCl,_~ CHFa + CHCla

(iii) Individual compounds Fluoroform, trifluoromethane, CHFa, is a gas, m . p . - - I 6 O ~ b.p.--840 almost completely inert chemically and physiologically. It may be obtained from silver fluoride and chloroform, or better from chloroform and antimony pentachloride/ hydrogen fluoride at 13~ under pressure (W. B. Whalley, J. Soc. chem. Ind., 1947, 66, 427). It is also produced Oll hydrogeaolysis of trifluoromethyl derivatives of metals and metalloids (A. M. Lovelace et al., "Aliphatic Fluorine Compounds", 1958, Chap. 12) and by reduction of trifluoromethyl iodide (W. T. Millar, E. Bergmann and A. H. Famberg, J. Amer. chem. Sot., 1957, 79, 4159 ). It is also produced by the hydrogenolysis of fluorocarbons (J. H. Simons, W. H. Pearlson and W. R. James, U.S.P., 2,494,o641195o):

502

HALOGENATED A L I P H A T I C HYDROCARBONS C3F8

N

3

H2

8oo0-> CHF8 + little CHgF~

and b y t h e oxidative fluorination of m e t h a n e (G. M. Whitman, U.S.P., 2,578,913/ 195I) : HF/O, CH4 CrO/A120. 5000~ CHF 8 Chloroform, trichloromethane, CHC1 v m.p. --63" 5 ~ b.p. 61.5 ~ d is I. 4989, n~)5 I. 44858, i s o b t a i n e d b y the direct chlorination of m e t h a n e or m e t h y l chloride (cf. p. 381) or b y the alkaline hydrolysis of compounds having a t e r m i n a l --CO---CC1 s grouping, e.g. chloral or trichloroacetic acid; such compounds are t r a n s i e n t i n t e r m e d i a t e s in t h e p r e p a r a t i o n of chloroform from alcohol, acetone, etc. and alkali or alkaline e a r t h hypochlorite solutions. I t is a colourless liquid with a pleasant smell and sweet taste, an excellent solvent for iodine and m a n y organic substances, and tends to a p p e a r as "chloroform of crystallisation". On mixing it with e t h e r a t e m p e r a t u r e rise occurs showing t h a t loose combination takes place. I n h a l a t i o n of the vapours produces anaesthesia (Simpson of Edinburgh, 1847). I r i s uninflammable, b u t burns with a greenish flame in the presence of alcohol. I t forms hexachlorobenzene when passed t h r o u g h a red hot tube. Reactions: (i) In presence of air in sunlight chloroform is oxidised slowly to phosgene. This can be p r e v e n t e d b y the addition of 1 % of alcohol. Phosgene is also formed b y oxidation with chromic acid. (2) Chlorination gives carbon tetrachloride. (3) Alkaline hydrolysis, a salt of formic acid. Dichlorocarbene is an interm e d i a t e p r o d u c t in this reaction (cf. p. 511). (4) Sodium ethoxide, ethyl orthoformate. (5) Alcoholic a m m o n i a at 18o o, a m m o n i u m cyanide and chloride b u t in the presence of potash energetic reaction occurs at o r d i n a r y t e m p e r a t u r e s : CHC13 + NH 8 + 4KOH = KNC + 3KC1 + 4H20 (6) Isocyanides, having a characteristic and repulsive smell, are formed when chloroform is h e a t e d with p r i m a r y amines and alkali. (7) S u b s t i t u t e d formamides are formed, in low yield, when chloroform is h e a t e d with a secondary amine in the presence of base: EtgN + CHC13

KOBut

-> H. CONEt9

(M. Saunders and R. W. Murray, T e t r a h e d r o n , 1959, 6, 88). (8) Chloroform will condense with ketones (except Ar.CO.Ar), aromatic aldehydes and a-substituted aliphatic aldehydes in the presence of alkali to give compounds of the t y p e R R ' . C (OH).CC18 ( R ' = H , Ar, or Alk) (R. Lombard. and R. Boesch, Bull. Soc. chim. Fr., 1953, 733, lO5O; E. D. Bergmann and D. Lavie, J. Amer. chem. Soc., 195 o, 72, 5o12; Ch. Weizmann, E. Bergmann and M. Sulzbacher, ibid., 1948, 7 o, 1189).

I

TRIHALOGENOPARAFFINS

503

(9) W i t h sodioacetoacetic ester, m - h y d r o x y u v i t i c acid, 4-hydroxy-5-methylisophthalic acid, is obtained (L. Claisen, Ann., 1897, 297, I). (IO) W i t h phenols and alkali, aromatic h y d r o x y a l d e h y d e s (Reimer-Tiemc~nn reaction) are formed. (II) Chloroform adds to olefiIlS in t h e presence of an acyl peroxide (M. S. Kharasch, E. V. Jensen and W. H. Urry, J. Amer. chem. Soc., 1947, 69, ILOO): R. CH =CHg. + CHC18

> R. CH 2. CHg. CC13

Addition to tetrachloroethylene in the presence of aluminium chloride yields I,I,I,2,2,3,3-heptachloropropane (M. W. Farlow, Org. Synth., Coll. Vol. II, 312): CC19.=CC19 + CHC1a

>

CC1a. CC19.CHC19

Bromoform, CHBr~, m.p. 7"8 ~ b.p. 149.5 ~ d ~5 2"9o2, is prepared b y the action of alkali h y p o b r o m i t e solution on acetone (G. Denigds, J. Pharm. Chim. Paris, 1891, [5], 24, 243). I t has also been obtained on electrolysis of a solution of acetone and potassium bromide, and from the action of aluminium bromide on chloroform. I t occurs in the distillation residues during bromine manufacture. Iodoform, CHI3, m.p. I2O ~ is formed b y the action of alkali and iodine on: (a) compounds of the type CH 3. CO. R where R is a h y d r o c a r b o n radical (steric hindrance m a y inhibit the reaction), CO~H or CO~R group b u t not an OH, I~H, or s u b s t i t u t e d OH or N i l 2 group; (b) compounds of the t y p e CH3. CHOH. R limitations as in group (a) ; (c) compounds such as oximes which readily hydrolyse to class (a); (d) compounds containing a - - C O . C H 2 . C O m or m C H O H . C H 2. CHOH-group, joined to carbon atoms which are not heavily substituted; (e) quinones and hydroquinones with at least one position ortho to the carbonyl or h y d r o x y l group u n s u b s t i t u t e d ; (f) m-dihydric phenols (e.g. resorcinoll; (g) certain compounds containing the l%Et group; (h) acetylene and its addition compounds e.g. C2H,.HgC12 (H. Booth and B. C. Saunders, Chem. and Ind., 195o, 825); (i) diethyl and ethyl n - b u t y l ketone (C. F. Cullis and M. S. Hashmi, J. chem. Soc., 1957, 1548). Malonic acid and iodine, in the presence of an oxidising agent (HIO4, K2Cr~O~, or KMNO4), yield iodoform (M. G. Brown, ibid., 1956, 2283). These considerations limit the v a l i d i t y of t h e "iodoform reaction" (Lieben reaction) as a test for C H 3 . C O - - and C H 3 C H O H - - groups. The mechanism of the simple iodoform reaction is similar to t h a t described for chloroform. Iodoform is m a n u f a c t u r e d on a small scale by the action of alkali and iodine on acetone and on a larger scale by the electrolysis of a solution of an alkali iodide in dilute alcohol or acetone, the correct p H being m a i n t a i n e d b y passing carbon dioxide t h r o u g h the mixture. Iodoform crystallises in brilliant yellow hexagonal plates and has a strong characteristic odour. It was discovered in 1832 by Serullas, and shown b y Dumas in 1834 to contain hydrogen. I t was first applied as an antiseptic to the t r e a t m e n t of wounds in 188o, b y Mosetig-Moorhof ill Vienna. I t slowly vaporizes at room t e m p e r a t u r e , can be distilled in steam, is soluble in alcohol and ether, but almost insoluble in water and petrol. The action

~0 4

H A L O G E N A T E D A L I P H A T I C HYDROCARBONS

3

of light and air slowly decomposes iodoform to CO2, CO, I~ and water. Hydrolysis (alcoholic potassium hydroxide or potassium arsenite) initially gives methylene iodide. Fluorochloro/orm, dichlorofluoromethane, CHC12F, b.p. 14.5 ~ (W. B. Whalley, loc. cir.); chlorofluoro[orm, chlorodifluoromethane, CHC1F v b . p . - - 4 ~ (Whalley), pyrolysis gives tetrafluoroethylene; bromochlorofluoro[orm, CHBrC1F, m.p. - - I 15~ b.p. 36" I~ mm. (K. L. Berry and J. M. Sturtevant, J. Amer. chem. Soc., 1942 , 64, 1599). i,I,I-Trifluoroethane, CF3CH 3, b.p. N47 ~ m.p.---lO7 ~ is prepared from vinylidene chloride and hydrogen fluoride (E. T. McBee and H. B. Hass, Ind. Eng. Chem., 1947, 39, 409) 9 For a general method for making CF3(CH2)nCH 3 by treating acids with sulphur tetrafluoride see W. R. Hasek et al., J. Amer. chem. Soc., I96O, 82, 543. Chlorination of ethyl chloride and ethylidene chloride in U.V. light gives a mixture of I,I,I-trichloroethane, CHaCCla, b.p. 750 and I,I,2-trichloroethane, CHIC1CHCI,, b.p. 1140 (J. D'Ans and J. Kautzch, J. pr. Chem., 19o9, [ii], 80, 3o5). The latter is prepared from chlorine and ethylene dichloride at room temperature, or preferably from chlorine and vinyl chloride in presence of ferric chloride. 1,2,3-Trichloropropane, CH~C1.CHC1.CHzC1, b.p. I58~ d 15 1.417, is prepared from (I) glycerol dichlorohydrin and thionyl chloride in diethylamine (G. Damens, Compt. rend., 1911, I52, 1316); (2) allyl chloride and sulphuryl chloride (M. S. Kharasch and H. C. Brown, J. Amer. chem. Soc., 1939, 6x, 3432); 1,2,3tribromopropane, m.p. I6-i7 ~ b.p. 219-22I ~ d 15 2.4114, from (I) epibromohydrin and phosphorus pentabromide; (2) bromine and allyl bromide (Org. Synth., Coll. Voh I, 1943, P. 521); (3) hydrogen bromide and 1,3-dibromopropene (A. Kirrmann and P. Renn, Compt. rend., 1936, 2o2, 1934).

(d) Polyhalogenoparao%ns. Polyhalogenoalkanes (i) Preparation (I) By direct hatogenation (cf. p. 379). The interhalogen compounds e.g. C1F 3, as well as individual halogens, have been used for the introduction of two halogens into organic compounds and for the fluorination of perchlorocompounds (W. K. R. Musgrave, in "Advances ill Fluorine Chemistry", Voh I, Butterworths, London, 196o ). (2) By addition of halogenoalkanes to halogenoalkenes. This may be a simple addition or a telomerisation process and m a y be catalysed by free radicals or by transition metal halides: C6HxaCH = C H s + CC14

peroxides or U.V.

> CeHlaCHC1CH~CC1a

(M. S. Kharasch et al., J. Amer. chem. Soc., 1947, 69, ILOO);

I

P OLYIIALOGENOPARAFFINS

505

CH2=CHg. + C B r 4 - > CHgBrCHICBr a CFaI + nCFz=CFg. ~

CFa(CF,--CF2)nI

(R. N. Haszeldine, J. chem. Soc., 1953, 3761; C. G. Krespan et al., J. Amer. chem. Soc., 1961, 83, 3424); CC19=CHC1 + CHC1a AlC~_> C H C I ~ C H C I ~ C C 1 a

(H. J. Prins, J. pr. Chem., I9I 4 [ii], 89, 414, 425;I.C.I. Ltd., B.P., 581,254/ 1946). (3) By coupling reactions: 2CaF~I + Zn Ac,O > CeF14

(A. L. Henne, J. Amer. chem. Soc., 1953, 75, 5750); 2CFgBrCFCII + H g . U'V"light-~ CFgBrCFC1CFC1CFgBr + Hglg.

(R. N. Haszeldine, J. chem. Soc., 1952, 4423). As an alternative, the coupling Call be carried out in dioxan solution with zinc. (4) By addition of halogen acids or halogens to olefins : 5CFsCF=CF 2 +

IF 5 + 21,.--+ 5CF3CFICF a

(R. D. Chambers, W. K. R. Musgrave and J. Savory, ibid., 1961, 3779)BrFa + Brz will add similarly to give perfluoroalkyl bromides. (5) By halogen exchange. Polychloroalkanes can be converted to polybromoalkanes by heating with aluminium bromide (C. Pourer, Compt. rend., 19oo, I3o, 1191). Similarly polyfluoroalkanes give polychloroalkanes with aluminium and other metal chlorides (W. C. Schumb and D. W. Breck, J. Amer. chem. Soc., 1952, 74, 1754): CF 4 A1C1,_..>CC14

Chlorides and bromides on heating with metal fluorides or hydrogen fluoride will give chloro- or bromo-fluorides (A. L. Henne, Org. Reactions, 1946, 2, 49). Sulphur tetrafluoride can also be used (C. W. Tullock et al., J. Amer. chem. Soc., I96O, 82, 51o7): r

4 + SF~

>r

+ CBrF3 + r

506

HALOGENATED

ALIPHATIC

HYDROCARBONS

3

Bromides and chlorides can be converted to iodides by sodium or calcium iodide in acetone or alcohol solution: CHFgCHg.Br NaI_+CHF2CHg.I

(F. Swarts, Bull. acad. roy. Belge, 19Ol, 7, 383). Direct treatment with chlorine will replace bromine or iodine: Br(CF~)3Br Cl, .--Br(CFg)3C1 Bromine will replace iodine. (6) From halogena~ed acids, esters, aldehydes or ketones and sulphur tetra/tuoride (W. R. Hasek et al., J. Amer. chem. Soc., 196o, 82, 543): CHgBrCHBrCHgCO~H ~

CH2BrCHBrCHgCF3

(7) By heating the silver salts of halogenated acids with iodine, bromine or chlorine (C. V. Wilson, Org. Reactions, 1957, 9, 332): CFC1BrCO~Ag El, > CFClzBr

(ii) Properties and reactions The lower polychloro- and polychlorofluoro-paraffins are used as solvents, refrigerants, and aerosols (A. K. Barbour, Chem. and Ind., 1961, 958). Some of their properties will be dealt with in discussing individual compounds and others in describing the preparation of halogenated alkenes and alkynes. In general, as the atomic weight of the halogen increases the stability of the polyhalogeno-alkane decreases because of the decrease in strength of the carbon to halogen bond and also because of the steric effect caused by packing the larger halogen atoms adjacent to one another as is well illustrated in the series CF~, CCh, CBr4 and CIr. The per/~uoroalkanes are particularly stable and are not attacked by concentrated nitric, fuming sulphuric or mixed acids, permanganate or chromic acid. They begin to break down on heating alone at ~ 700 o and with sodium or potassium at 600o-8000 . Because of the great stability of the fluorocarbon skeleton, they give rise to homologous series such as CnF~n+lI andCnF~n+lCO~H containing functional groups similar to those arising from the hydrocarbons i.e. CnH~n+lI, etc. In many of their reactions the perfluoroalkyI halides differ from the corresponding hydrocarbon compounds because of the different electronic forces in the molecules, fluorine being the most electronegative element, having lone pairs

I

1"o LY HALO GE N 0 P ARAFFI N S

507

of electrons and, when a t t a c h e d to carbon, being able to exhibit a hyperconjugative effect ill the opposite sense to t h a t exhibited b y hydrogen. The reactions of these polyhalogeno-compounds are mainly elimination reactions when there is hydrogen in the molecule, and dehalogenation reactions. In the former the order of elimination is H I > H B r > HC1 > H F and in the latter, I , > B r , > C12. As yet there are no cases in the aliphatic series in which fluorine alone has been eliminated b u t in the alicyclic series perfluorocyclohexane can be converted to hexafluorobenzene b y passing the vapour over h e a t e d iron gauze (J. C. Tatlow et al., Tetrahedron, 196o, 9, 24o). Chlorine is eliminated preferentially when it is present in this t y p e of compound (R. H. Mobbs a n d W. /4. R. Musgrave, Chem. and Ind., 1961, 1268). The perfluoroalkyl halides exhibit the usual order of r e a c t i v i t y i.e. iodide > bromide > chloride, the chlorides being almost as inert as the perfluoroalkanes. These halides do not undergo the usual nucleophilic reactions of the alkyl 6|

fl~

halides, the C-I bond being polarised in the opposite sense F 3 C - - I , b u t t h e y are reduced to m o n o h y d r o - c o m p o u n d s b y lithium a l u m i n i u m h y d r i d e (J. C. Tatlow and R. E. Worthington, J. chem. Soc., 1952, 1251; J. Banus et al., ibid., 1951, 6o; M. Hauptschein et al., J. Amer. chem. Soc., 1956, 78, 68o). The iodides and bromides also undergo free radical reactions which involve breaking the C-halogen bond and the iodides form organometallic and organometalloid derivatives. The c h e m i s t r y of halogen-containing compounds is reviewed a n n u a l l y (E. T. McBee et al., Ind. Eng. Chem., 1948, et seq.) and for more details see E. H. Huntress, "Organic Chlorine Compounds", Wiley, 1948; J. H. Simons, "Fluorine Chemistry", Vols. I and 2, Academic Press 195o; W. K. R. Musgrave, " T h e Reactions of Organic Fluorine Compounds", Quart. Reviews, 1954, 8, 331; A. M. LoveIace et aI., "Aliphatic Fluorine Compounds", Reinhold, 1958; M. Stacey et al., "Advances in Fluorine C h e m i s t r y " , B u t t e r w o r t h s , 196o, 1961, 1963 et seq.; M. Hudlicky, " C h e m i s t r y of Organic Fluorine Compounds", P e r g a m o n Press, i96I.

(iii) Individual compounds Carbon tetrafluoride, tetrafluoromethane, CF 4, f . p . - - I 8 7 ~ b . p . - - I 2 8 ~ is a v e r y stable colourless gas. It is among the few carbon compounds t h a t can be prepared directly from the elements (0. Rut~ and R. Keim, Z. anorg. Chem., 193o, 192, 249) b u t a more practicable m e t h o d is to t r e a t carbon monoxide, carbon dioxide or phosgene with sulphur tetrafluoride (W. R. Hasek et al., J. Amer. chem. Soc., 196o, 82, 543). I t dissolves in w a t e r w i t h o u t hydrolysis. Carbon tetrachloride, tetrachloromethane, CCI~, b.p. 76.7 ~ f . p . - - 2 2 . 9 ~ d o I "631, is formed (I) b y the action of chlorine on chloroform in sunlight, or in presence of iodine as a catalyst; (2) b y the action of chlorine on carbon disulphide at 2o-4 o~ C2C14 and C,CI 6 being formed at the same time (V. Meyer, Ber., 1894, 27, 316o) (a technical modification uses a column reactor and gives only carbon tetrachloride a n d s u l p h u r J. Beaublossom, U.S.P., 2,287,225/I942) ; (3) b y heating

508

HALOGENATED A L I P H A T I C HYDROCARBONS

3

carbon disulphide with sulphur monochloride in the presence of small quantities of iron: CS9. -]- 2S2C12 = CC14 + 6S

(Miiller and Dubois, G.P., 72,999/1893). F o r the p r e p a r a t i o n of the pure substance, see P. Gunther, H. D. yon der Horst and G. Cronheim, Z. Elektrochem., 1928, 34, 616. Carbon tetrachloride must not be dried over sodium as t h e y form an explosive m i x t u r e (H. Staudinger, Angew. Chem., 1922, 35, 658) 9 I t is a pleasant-smelling liquid, solidifying to a crystalline mass at m3o0, and is an excellent solvent. I t is used as a fire extinguishing liquid b u t suffers from the disadvantage of producing phosgene in the process. I t decomposes when h e a t e d with alcoholic potash: CC14 + 6KOH = KgCO3 + 3H~O + 4KC1 W h e n the vapours are conducted t h r o u g h a red hot t u b e decomposition occurs and C~C14 and CzC1e are produced. The l a t t e r can also be produced b y means of aluminium amalgam. F o r reactions of carbon tetrachloride with phenols and aromatic amines see Vol. I I I . Carbon tetrabromide, tetrabromomethane, CBr 4, m.p. 9I ~ b.p. 189.50 (decomp.) is formed from bromine and carbon disulphide in the presence of iodine. It is most c o n v e n i e n t l y prepared b y the exhaustive bromination of acetone in the presence of alkali (W. H. Hunter and D. E. Edgar, J. Amer. chem. Soc., I932, 54, 2025) or by t r e a t i n g carbon t e t r ~ h l o r i d e with hydrogen bromide in the presence of a l u m i n i u m chloride. I t crystallises in shining plates, insoluble in water, soluble in organic solvents. I t has been used for selective b r o m i n a t i o n of the side chain of alkylbellzenes (W. H. Hunter and D. R. Edgar, loc. cir.). Carbon tetraiodide, tetraiodomethane, CI 4, d "~ 4" 32, is formed when a mixture of carbon tetrachloride and carbon disulphide is h e a t e d with aluminium iodide and can also be p r e p a r e d from iodoform and potassium hypoiodite (]. F . Durand, Bull. Soc. chim. Fr., I927, [iv], 4I, I25I). It crystallises from ether in dark-red regular octahedra, which sublime on heating. On exposure to air, it decomposes into carbon dioxide and iodine, a change which is accelerated b y heat and in solution (R. Dubrisay aIxd G. Emschwiller, ibid., I935, Iv], 2, 127). W i t h h y d r o g e n at I4O~ it decomposes into h y d r o g e n iodide and iodoform. Trichlorofluoromethane, CC18F, b.p. 23.8 ~ m.p. - - I I I ~ dichlorodifluoromethane, CC1,Fv b.p. m 2 9 . 8 0 , m.p. m I 5 8 0 ; and chlorotrifluoromethane, CC1F 8, b.p. - - 8 1 . 5 ~ m.p. N I 8 I 0, are all p r e p a r e d b y the action of a n h y d r o u s h y d r o g e n fluoride on carbon tetrachloride (H. W. Daudt and M. A. Youker, U.S.P., 2,oo5,7o5; 2,oo5,7o9; 2,oo5,7IO/I935). Because of their inertness t h e y are used as refrigerants and aerosol propellants. Bromotrifluoromethane, C B r F 3, b . p . - - 5 8 ~ can be prepared from silver trifluoroacetate (M. Hauptschein et al., J. Amer. chem. Soc., 1952, 74, 1347) or fluoroform and bromine (T..[. Brice et al., ibid., 1946, 68, 968). Dibromodifluoromethane, CBr,Fz, b.p. 23 o. is prepared b y brominating difluoromethane (R. P. Rub and R. A. Davis, U.S.P., 2,639,3Ol and 2,658,o86[I953) or b y t r e a t i n g carbon t e t r a b r o m i d e with hydrogen fluoride a t

I

P O LYHALO

GE N O P ARAFFI

N S

509

35 ~ in the presence of alumina impregnated with metallic halides (idem, B.P., 8o5,5o3/I958 ). Both CBrF 3 and CBr2F 2 have been used as chain-transfer agents (M. Haupeschein et al., J. Amer. chem. Soc., 1958, 8o, 851) and both are very efficient, non-toxic fire extinguishers (A. K. Barbour, Chem. and Ind., 1961, 966). Trifluoromethyl iodide, trifluoroiodomethane, CF3I, b . p . - - 2 2 - 5 ~ is prepared by heating silver trifluoroacetate with iodine (R. N. Haszeldine, J. chem. Soc., 1951, 584). It has been used considerably as a chain-transfer agent in telomerisation reactions with ethylene, acetylene, tetrafluoroethylene and other halogenated olefins (W. K. R. Musgrave, Quart. Reviews, 1954, 8, 331) and in making trifluoromethyl derivatives of metals and metalloids (Lovelace et at., op. cir., p. 307). Acetylene tetrachloride, s-tetrachloroethane, CHC1,CHC1 v b.p. I46~ is made by direct combination of chlorine and acetylene under conditions designed to avoid explosive reaction; solutions of chlorine and acetylene ill tetrachloroethane are mixed in the presence of antimony pentachloride (P. Askenasy and M. Mugdan, B.P., I8,6o2/I9O4), ferric chloride (E. Hoo[er and M. Mugdan, U.S.P., 985,528/ I9IO), aluminium chloride (A. Mouneyrat, Compt. rend. 1898, I26, 18o5) or iron (G. Ornstein, B.P., 2375/1911). Dilution of the reaction mixture with steam (Holverkohlungs Ind. A.-G., G.P., 387,45211921) or with all inert gas (J. H. Lidholm, B.P., 22,o94/I9O5) has been recommended. It is a good solvent, but its vapour is toxic. On further chlorination, in sunlight or in presence of aluminium chloride it gives pelltachloroethane and hexachloroethane. s-Tetrabromoethane, CHBr~.CHBr, b.p. 125~ mm. is obtained from acetylene and bromine (R. G. O'Meara and J. B. Clemmer, Bur. Mines Report, 2897/ 1928). Zinc dust and alcohol convert it into s-dibromomethylene, whilst reaction with benzene and aluminium produces anthracene, together with as-diphenylethane and anthraquinone (R. Anshi~tz, Ann., 1886, 235, 163). Pentachloroethane, C,HC15, b.p. 1620 is obtained by the addition of chlorine to trichloroethylene in presence of catalysts, or in ultraviolet light. Perchloroethane, hexachloroethane, C2C1e, m.p. 187 o (sublimes), is prepared by heating carbon tetrachloride with aluminium amalgam under reflux (K. A. Hoffmann and E. Seller, Ber., 19o 5, 38, 3058). It is formed, together with hexachlorobenzene, when an electric arc is struck between carbon electrodes in an atmosphere of chlorine (W. yon Bolton, Z. Elecktrochem., 19o2, 8, 169). Commercially, it has been made by chlorinating s-tetrachloroethane in the presence of aluminium chloride (Mouneyrat, loc. cir.). Hexachloroethane, a colourless crystalline solid with a camphor-like smell, sublimes on heating. With alkali above 2oo ~ oxalic acid is formed; ethylene, hydrogen and oxalic acid are produced when it is treated with alcoholic potassium hydroxide at I oo ~ Heating with antimony pentachloride above 45 ~ yields carbon tetrachloride (E. Hartman, Ber., 1891, 24, lO23). It is converted to tetrachloroethylene by catalytic reduction (P. Sabatier and A. Mailhe, Compt. rend., 19o4, 138, 4o9), by alcoholic potassium hydrogen sulphide and by zinc and sulphuric acid. Hexabromoethane, C~Br6, decomposing at 2oo-21o ~ into bromine and tetra-

510

HALOGENATED ALIPHATIC HYDROCARBONS

3

bromoethylene, C~Br4, is obtained by the reaction of bromine with acetylene tetrabromide in the presence of aluminium bromide (A. Mouneyrat, Compt. rend. 1898, I27, 109). I,I,2-Trichloro-I,2,2-trifluoroethane, CC12FCC1F9, b.p. 47 ~ m . p . - - 3 6 ~ n~ 1"35572, d~5 I. 56354, is available commercially and can be prepared from perchloroethane and SbF3C1z (E. G. Locke et al., J. Amer. chem. Soc., 1934, 56, 1726) together with other chlorofluoroethanes. On warming with aluminium trichloride isomerisation occurs to give mainly I,I,I-trichlorotrifluoroethane, CC13CF3, b.p. 46~ m.p. I4 ~ n ~ I. 361o (W. T. Miller et al., ibid., i95 o, 72, 7o5). 1,2-Dichloro-I,I,2,2-tetrafluoroethane, CC1F~CC1Fg, b.p. 4 ~ m.p. --94 ~ n ~ I. 29o, d~~ I. 47 o, is prepared from CCI~FCC1F~ b y t h e action of SbF3C1 ~ (A. L. Henne, Org. Reactions, 1944, 2, 65). It is a very stable compound and is used as an aerosol propellant in cases where particular care is necessary (foods, cosmetics). Hexafluoroethane, CsF6, b . p . - - 7 9 ~ m . p . - - I O I ~ is made by the direct fluorination of ethane (E. A. Tyczkowski and L. A. Bigelow, J. Amer. chem. Soc., 1955, 77, 3~176 "Fluothane", 2-bromo-2-chloro-I,I,I-trifluoroethane, CF3CHBrC1 , b.p. 5o~ is a good anaesthetic and its use eliminates the explosion hazard associated with diethyl ether. There are three methods of preparation which illustrate well the reactions of polyhalides (I.C.I. Ltd., ]3.P., 767,779/I957; U.S.P., 2,921,o98-911961): CC19=CH 2 ~

CClzBrCHgBr HF_+ CF3CH~Br c1,_+ CFsCHBrC 1

(i)

CH3CC13 HF_+ CH3CF3 c12-+ CF3CHgC1 Br2+ CF3CHBrC1

(ii)

CC19=CHC1 HC1 > CC13CHgC1 HF__>CFsCHzC1 Br,+ CF3CHBrC1

(iii)

Pentafluoroahyl iodide, pentafluoroiodoethane, C~FsI, b.p. 13 ~ n~SS 1.3378, prepared by the addition of iodine fluoride, IF, to tetrafluoroethylene and pentafluoroethyl bromide, bromopentafluoroethane, CzFsBr, b . p . - - 2 1 ~ by the addition of bromine fluoride to tetrafluoroethylene (R. D. Chambers, W. K. R. Musgrave and J. Savory, J. chem. Soc., 1961, 3779). A series of polyhalopropanes Call be prepared by condensing halogenated ethylenes with halogenated methanes in the presence of aluminium chloride (H. J. Prim, J. pr. Chem., 1914, [ii], 89, 414) or by using peroxide catalysts (M. S. Kharasch et al., J. Amer. chem. Soc., 1947, 69, ILOO): CBr4 + CH2--CH9

> BrCHzCH2CBr3

n-Heptafluoropropyl iodide, CF3CF~CF~I, b.p. 41~ is prepared from silver heptafluorobutyrate and iodine (C. V. Wilson, Org. Reaction, 1957, 9, 332). Isoheptafluoropropyl iodide, CFsCFICF3, b.p. 38~ n~~ I. 32631 is prepared from CF3CF= CF~ and IF, a method which always gives the secondary iodide whenever possible (Chambers, Musgrave, and Savory, loc. cir.).

I

HALOGENATED

ALKENES

511

2. Halogen derivatives of the alkenes These fall into two classes: (a) The halogenocarbenes. (b) Halogen derivatives of olefins.

(a) Halogenocarbenes (i) Pr@aration The mono- and di-halogenocarbenes have already been referred to in the preceding chapter (see p. 4Ol). They are formed and have a definite, though transitory, existence in the following reactions" (I) The action of a base on a haloform (J. Hine, J. Amer. chem. Soc., 195o, 72, 2438; W. yon E. Doering and A. K. Hofmann, ibid., 1954, 76, 6162; Hine, A. M. Dowell and J. E. Singly, ibid., 1956, 78, 479; Him and K. Tanabe, ibid., 1958, 8o, 300): H20 + CC18e......> :CClz + C1e

CHC18 + OH e ~

CHCIF2 + i-PrO e ---+ i-PrOH + CC1F~e ----+ :CF~ + C1e (2) The action of lithium alkyls on carbon polyhalides (W. T. Miller and C. S. Y. Kim, ibid., 1959, 81, 5008; G. L. Closs and L. E. Closs, ibid., 196o, 82, 5723, 5729): CBrC1a + C4HgLi --C4HgBr + LiC1 + :CCI~ CHzC12 + CH3Li --CH 4 + LiC1 + :CHC1 (3) The alkaline decarboxylation of trihalogenoacetic acids (W. M. Wagner, Prec. chem. Soc., 1959, 229): CClaC09.e

>

COo. + CClae - > C1| + : CClo.

(4) The action of alkoxides on trihalogenoacetates (esters) (W. E. Parham and E. E. Schweitzer, J. org. Chem., 1959, 24, 1733): CClaCO~R + RO e ---+ (RO)o.CO + CC13e-----+C1| + :CCI~ (5) The thermal breakdown of trihalogenoacetates (J. M. Birchall, G. W. Cross and R. N. Haszeldine, Prec. chem. Soc., 196o, 81; W. M. Wagner, H. Kloosterziel and S. Ven, Rec. tray. chim., 1961, 8o, 74 o) : CFzC1CO2e ---~ CO9. + CFoC1| ---+ C1~ + :CF2

512

HALOGENATt~D ALIPHATIC HYDROCARBONS

3

(6) The pyrolysis of polyhalogenoalkylmetalloid halides (W. Mahler, J. Amer. chem. Soc., 1962, 84, 46oo; W. I. Bevan, R. N. Haszeldine and J. C. Young, Chem. and Ind., 1961, 23, 789): xoo9 (CFa)sPF , - - - - - - + :CF,

(7) The decomposition of phenyltrihalogenomethyl mercurials (D.Seyferth et aI., J. org. Chem., 1963, 28, 1164): P h . Hg. CBrC12 m _ + P h . H g B r + :CC19

(ii) Properties and reactions A carbene can have two unshared electrons and react as a radical, or the electrons can be paired. In the latter case it will have a pair of shared electrons and an empty orbital and can, theoretically at least, react either as a nucleophile or an electrophile. Thus it may be described as the St. Paul of the chemical reagents (Ist Corinthians, Chapter 9, Verse 22). Whether tile nucleophilic or electrophilic character will predominate depends on the other groups attached to the central carbon atom; in the halogenocarbenes tile electrophilic character predominates. Halogenocarbenes will add to triple bonds to give cyclopropenes and bicyclobutanes (Mahler, loc. cir.)" CFa

9c ~ + cF~c_=CCF~~

CF a

\ ~ / x

/

F~

Fz

= ~ > cF~

\/ /~

cF~

Fg.

with olefins they give cyclopropanes (Birchall et al., loc. cir.). The rate and stereospecificity of the addition of dibromocarbene to olefins has been investigated by P. S. Skell and A. Y. Garner, J. Amer. chem. Soc., 1956, 78, 5430. Aromatic hydrocarbons such as benzene (G. L. Closs and C. E. Closs, Tetrahedron Letters, 196o, No. IO, p. 38) and anthracene (R. W. Murray, ibid., 196o, No. 7, P. 27) undergo ring expansion with mono- and di-chlorocarbenes respectively"

[;]

Compounds possessing an atom with an available lone pair of electrons (amines or carbanions) will react readily with the electrophilic halogenocarbenes; secondary amines give eventually dialkylformamides"

2

HALOGENATED ALKENES @ RR'NH

+

"CCI~: ~> R R ' N - - H

----+ R R ' N - - C . - - H

""

513 " RR'N--C--H

/ ' ~

|

[

CI

a

CI

[l

O

and triphenylphosphine gives alkylidenephosphoranes" Ph3P" +

"CXt---+ P h 3 P = C X ~ .

(X = CI or F)

These can be used in a Wittig reaction to give olefins" Ph3P=CC19. + PhgC=O----+ PhaC=CC12

These reactions, and others in which halogenocarbenes are used as reagents to produce spiranes, allenes, allylic compounds, dienes, cyclopropenones and compounds with a cyclopropenyl cation are summarised by H. Kloosterziel, Chem. Weekblad, 1963, 59, 77, who gives numerous references to the original literature, and E. Chenoporos, Chem. Reviews, 1963, 63,235.

(b) Halogen derivatives of olefins (i) Preparation Many of the methods employed are similar to those used for alkyl halides (P. 479 et seq.) and olefins (p. 4Ol et seq.). Specific examples are given under individual compounds (p. 517 et seq.). (I) Dehalogenation of polyhalogenoalkanes. (2) Dehyclrohalogenation of polyhalogenoalkanes. (3) From olefinic alcohols and hydrogen, phosphorus or thionyl halides. (4) Direct, high temperature halogenation of alkenes at the a-carbon atom (allylic position): C1, CHg----CHCH 3 300_6o0O-+CH~=CHCH2C1 + HC1

(H. P. A. Groll and G. Hearne, Ind. Eng. Chem., 1939, 3I, 153o). (5) Hal~genation of alkenes in the allylic position with N-bromosuccinimide, etc." RCHgCH = C H R '

> RCHBrCH--CHR'

(K. Ziegler et al., Ann., 1942, 551, 80; C. Djerassi, Chem. Reviews, 1948, 43, 271). The reaction is catalysed by benzoyl peroxide; for mechanism see M. J. S. Dewar, "The Electronic Theory of Organic Chemistry", Oxford Univ. Press, London, 1949, 273 and B. P. McGrath and J. M. Tedder, Proc. chem. Soc., 1961, 80.

514

HALOGENATED ALIPHATIC HYDROCARBONS

3

(6) Controlled addition of hydrogen halide to an alkyne. The following methods are of particu]ar interest in making fluorinated olefins: (7) Addition of halogenoalkanes to alkynes : CF3I + C H - - C H ~

CF3CH = C H I

CF3C==--CH+ CC13I- - + CFsCHI=CHCC1 a (R. N. Haszeldine et al., J. chem. Soc., 195o, 2789; 1952 , 3483; 1953, 922). (8) Free-radical addition of a halogenated ol~fin possessing a labile halogen atom to an olefin or another halogenated olefin : C F 2 = C F I + CH~=CH 2 ~

CF~=CFCH,CH~I

(J. D. Park et al., J. Amer. chem. Soc., 1956, 78, 59). (9) Pyrolysis, at 200-35 ~ ,of the sodium salts of carboxylic acids for terminally unsaturated fluoroalkenes : CF3(CFg)nCO~Na ~ ~~ CF3(CFg.)n_zCF=CF z + CO 2 + N a F

(A. M. Lovelace et al., "Aliphatic Fluorine Compounds", 1958 , p. lO7). (IO) Pyrolysis of fluorinated cyclobutenes: CF~--CH 7oo'C I II zo ram. ~ CFz = C H - - C H = C F t CFI--CH

(j. L. Anderson et al., J. Amer. chem. Soc., 1961, 83, 382). (II) Simultaneous dehalogenadon and coupling with copper powder at 14o-2oo0: 2C1CF~CF2CC13 + Cu ~

C1CFgCFgCC12CC19CFgCFgC1 + Cu9C19

C1CFg.CFgCC1=CC1CFgCFiC1 + Cu9C19.+ - ~

(C. G. Krespan et al., ibid., 1961, 83, 3424). (12) Heating a fluorinated acid chloride with nickel carbonyl and I,I-dichIoro2,2-difluoroethylene : 2RFCOC1 + Ni(CO)4 ~ RFCO-

2RFCO" + NiCIg. + 4CO > R F- + CO

RF- + CFg=CC19.---+ RFCFg--CC112RFCF2CC19. ---+ RFCF~CCI~CC19CFgRF RFCF2CC19CC19.CFgRF + Ni(CO) 4 ~

RFCFgCCI=CCICFgRF + NiC12 + 4CO

where R~ represents a fluorinated radical (Kreslban et al., loc. cir.).

2

HALOGENATED ALKENES

515

(ii) Properties and reactions In reactions involving the halogen atoms vinyl halides are much more inert than alkyl halides because the conjugation of lone pairs of electrons on the halogen with the ~ electrons of the double bond results in a stronger carbon to halogen bond.

C~M2NN"Ct/cl

\

N

Although this discourages replacement of the halogen by nucleophiles it does not prevent the formation of Grignard reagents which are prepared best from the bromides in tetrahydrofuran solution (H. Normant, Compt. rend., 1954 , 239, 151o): (trace EtBr) CH3CH=CHBr + Mg - - - ~

CH3CH=CHMgBr

Trifluorovinyl bromide and iodide also form Grignard reagents which undergo normal reactions (J. D. Park et al., J. Amer. chem. Soc., 1956, 78, 59; H. D. Kaesz, ibid., 196o, 82, 6232). Vinyl halides undergo the normal electrophilic and free radical addition reactions of hydrocarbon alkenes giving halogenated alkanes (p. 479) the structure of the final product in electrophilic addition being governed by the above mentioned polarisation of the double bond. As the n u m b e r of halogen atoms in the molecule increases the t e n d e n c y to undergo electrophilic additions decreases and t h a t to add nucleophilic reagents increases because of the reduction in electron density resulting from the increase in electronegative substituents. This t e n d e n c y is more pronounced when the halogens are directly a t t a c h e d to the u n s a t u r a t e d carbon atoms and is most pronounced ill the case of the fluorinated olefins. The extensive literature on electrophilic, nucleophilic and free radical reactions of these compounds has been reviewed. (W. K. R. Musgrave, Quart. Reviews, 1954, 8, 33I). Although the nucleophilic additions are less well known in the case of the o t h e r halogens, p a r t l y because they, being bigger t h a n fluorine, introduce the factor of steric hindrance into the problem, the p h e n o m e n o n is shown clearly b y trichloroethylene which reacts with sodium ethoxide to give dichlorovinyl ether. In this case the alcohol has been added across the double bond and t h e n HC1 has been eliminated: CC19=CHC1 + EtOH EtOCCI~ICHzC1

>

EtOCC19--CH~C1

NaOEt -+ EtOCCI=CHC1 + NaC1 + EtOH

516

HALOGENATED ALIPHATIC HYDROCARBONS

3

Numerous long chain polymers and co-polymers of the halogenated olefins have been prepared by standard methods; some of these will be described with the individual olefins; for review see C. R. Schildknecht, "Vinyl and Related Polymers", Wiley, New York, 1952. Short chain polymers or telomers have also been m a d e using chain-transfer agents as described earlier (W. E. Hanford, U.S.P., 2,443,oo3/I948 ; Hanford and R. M. Joyce, U.S.P., 2,562,547/1951): nC~F4 + CHaOH ----+ H(CF~CF,)nCH2OH (n = I ~ 12) nC,F, + (EtO),P.OH

-.~ H(CF2CFt)aPO(OH)~ (after hydrolysis).

The fluorinated olefins will also form cyclic dimers not only among themselves but also with hydrocarbon olefins and dienes (D. D. Co~man et al., J. Amer. chem. Soc., 1949, 71, 490; J. R. Lather et al., ibid., 1952, 74, 1693): CFg.--CCI~ ~ [ [ CFi--CC12

2CFg=CCI~

CF9 CH, I! + II

CF,

CH--CH =CH,.

CF,--CH9 ---~ I [

CFg--CH--CH =CH,

c!F,_~ CFg--CH~ CHg--CF, I I I I CF,--CHm CH---CF,

With acetylene or its derivatives cyclobutenes are formed (J. L. Anderson et al.,

ibid., 1961, 83, 382): CF~

I! CF,

C--CH2OH

+ Ill CH

CF,--C--CH,OH

I~-~' I

II

CF~--CH

These cyclic butanes and butenes do not appear to be formed by unsubstituted or chlorinated alkenes. Halogenated alkenes with halogen atoms attached to the unsaturated carbon atoms can be dehydrohalogenated or dehalogenated to alkyaes (see p. 522). Alkenes in which a halogen atom is attached to the x-carbon atom i.e. allyl halides, CHg--CH--CHaX show a remarkable enhancement of halogen activity and allyl chloride is approximately eighty times as active to nucleophiles as n-propyl chloride. Reaction of a simple allyl halide with a nucleophile can lead to only one product, CHz=CH~CH2X + OEt e ---+ CH~=CHCH~OEt + X |

HALOGENATED ALKENES

2

517

but if the molecule has other groups substituted in the I or 3 position so t h a t the skeleton is not symmetrical, the product formed depends on whether the process occurs by a unimolecular or a bimolecular mechanism. Thus 1-methylallyl chloride on reaction with ethoxide ion by second order kinetics gives Imethylallyl ethyl ether: CHbCHC1CH--CH 2 + OEt e ----+ CHbCH(OEt)CH--CH z + Cl | Similarly crotyl chloride gives crotyl ethyl ether, CHbCH--CHCH2X + OEt ~ ---+ CHbCH=CHCHgOEt + X e but if the reaction is carried out so t h a t a unimolecular mechanism applies (low concentration of OEt e) then either chloride gives both ethers, an equilibrium being set up between the two chlorides by an aniontropic rearrangement (C. K. Ingold, "Structure and Mechanism in Organic Chemistry", 1953, 586-6oi) : C - - C = C ~ [ C ~ C - - C ] m + Xe ~ C = C ~ C

J

l

x

x

For reactions and rearrangements of allylic halides see E. A. Braude (Quart. Reviews, I95O, 4, 4~ and E. D. Hughes (ibid., 1951, 5, 245). As a result of the ease with which allylic halogen atoms react, it is essential t h a t any nucleophilic addition reactions to the olefinic bond in such compounds should be carried out under very mild conditions. Even trifluoromethyl groups, which are normally very stable indeed, are readily hydrolysed to carboxyl groups when adjacent to a double bond: C--CF

~

>C--CO,H + 3HF

The g r e a t r e a c t i v i t y of allyl halides, particularly the bromides a n d iodides, enables t h e m to react v e r y readily with Grignard reagents, so providing a general m e t h o d for the p r e p a r a t i o n of alkenes with t e r m i n a l double bonds" CHz=CHCHzX + RMgX ----+ CHz=CHCH2R + MgX~ Allyl halides, unlike vinyl halides, do not homopolymerise easily. T h e y will co-polymerise b u t t e n d to give shorter chain polymers because t h e y act as chain-transfer agents (Schildknecht, loc. cit., p. 391).

(iii) Individual compounds Vinyl fluoride, fluoroethene, C H 2 = C H F , b.p. --72~ is made by passing hydrogen fluoride and acetylene over carbon pellets containing mercuric chloride

518

HALOG]~NATED ALIPHATIC HYDROCARBONS

3

(A. E. Newkirk, J. Amer. chem. Soc., 1946, 68, 2467). It will homopolymerise and form co-polymers with ethylene, tetrafluoroethylene, methyl methacrylate etc. (C. E. Schildknecht, loc. cir.). Vinyl chloride, b.p. N I 4 ~ m.p. NI6O ~ is prepared commercially from acetylene and hydrogen chloride but more conveniently in the laboratory by dropping ethylene dichloride into warm aqueous alcoholic caustic alkali (cf. Schildknecht, loc. cir., p. 389). It is polymerised to polyvinyl chloride (P.V.C.) and co-polymerised with numerous monomers by a variety of methods giving products used as rubber and leather substitutes. Vinyl bromide, b.p. 16 ~ m.p.--138~ is prepared from ethylene dibromide (M. S. I4harasch et al. J. Amer. chem. Soc., 1933, 56, 2521). It will polymerise on irradiating with u.v. light but the polymer breaks down on heating (H. Staudinger et al., Helv. I93O, x3, 8o5). Vinyl iodide, b.p. 5 6~ n~~ I. 5384, prepared from di-iodoethane and sodium ethoxide (J.Spence, J. Amer. chem. Soc., 1933, 55, 129o) has been polymerised in the presence of sodium thiosulphate because free iodine retards the process (V. V. Korshak et al., J. Gen. Chem. U.S.S.R., 195o, 20, 2080, 2153). Vinylidene fluoride, I,I-difluoroethene, C H ~ = C F 2, b.p. ~ 8 4 ~ prepared from trichloroethylene (E. T. McBee et al., Ind. Eng. Chem., 1949, 4 x, 7o): CCI~=CHC1 + HF

Zrl

-> CC1F2CH~C1 CH,CONHt > CF~=CH t

can be polymerised by emulsion techniques or by peroxides under high pressure. One of its most important co-polymers in the elastomer formed with hexafluoropropene, "Viton A" (S. Dixon et al., Ind. Eng. Chem., 1957, 49, I687), the most stable elastomer so far produced. It can be heated for long periods to N 2oo 0 and is very resistant to concentrated acids and alkalis, aromatic and aliphatic hydrocarbons and steam. Vinylidene chloride, I,I-dichloroethene, b.p. 32~ n~~ 1.4249 is prepared from, I,I,2-trichloroethane, in the laboratory with potash (E. Baumann, Ann., 1872: z63, 3o8), but commercially by pyrolysis at 4o0 o (Schildknecht, loc. cir., p. 448)1 CH~C1CHCI~

4000

9 CH~=CC12 + HC1

I t homopolymerises and forms co-polymers easily. The co-polymer with viny fluoride ("Saran", Dow Chemical Co.) is used for pipes carrying aqueous acids and alkalis, for fishing nets, and woven upholstery fabrics. The preparation and polymerisation of other vinylidene halides, CH2=CBrC1, C H t = C B r F , CH~=CC1F are described by Schildknecht (lot. cir.). I,I-Dibromob.p. 920 and I-bromo-I-chloro-eghene, b.p. 830 undergo auto-oxidation to bromoacetyl bromide and a mixture of chloroacetyl bromide and bromoacetyl chloride respectively. 1,2-Difluoroethylene, 1,2-difluoroethene, C H F = C H F , prepared by the dehalogenation of I-bromo-I,2,2-trifluoroethane (N. C. Craig and E. A. Entemann, J. Amer. chem. Soc., 1961, 83, 3o47) is a mixture of cis-(8o %) and trans-(2o %) isomers separable by fractional distillation; cis-isomer b.p. --26 ~ trans-isomer

2

I-IALO GENATED ALKENES

519

b.p. --53 ~ which can be stored under ordinary conditions without isomerisation. Craig and E n t e m a n n discuss the thermodynamics of cis-trans isomerisation which is brought about by iodine atoms and refer to corresponding work on the other symmetrical dihalogeno-ethylenes. 1,2-Dichloroethylene, 1,2-dichloroethene, cis-, m . p . - - 8 o ~ b.p. 60 ~ n ~ I "4519; trans-, m . p . - - 5 o~ b.p. 48~ n ~ I. 449o, form co-polymers. 1,2-Dibromoethene, cis-, m.p. M53 ~ b.p. 112.5 ~ n ~ -5 1-5431; trans-, m . p . - - 6 . 5 ~ b.p. lO8 ~ n ~ "5 1.55o 5. 1,2-Di-iodoethene, cis-, m . p . - - 1 4 ~ b.p. 72.5~ mm.; trans-, m.p. 78~ b.p. 77~ ram. A mixture of cis- and trans- di-iodoethenes is obtained by heating acetylene with iodine at 14o0-16o 0 (E. H. Keiser, Amer. chem. J., 1899, 2x, 261). Trifluoroethene, C F , = C H F , b . p . - - 5 1 ~ from I,I,2-trichlorotrifluoroethane by dechlorination, addition of hydrogen bromide and subsequent removal of chlorine and bromine (R. N. Haszeldine and B. R. Steele, J. chem. Soc., 1954, 3747) will add such reagents as chlorine, bromine and methyl alcohol (P. Tarrant, "Fluorine Chemistry", Vol. II, 1954, P. 225): CF2=CH F + CH30 H

NaOH

> CH3OCF, CH2F

Trichloroethylene, trichloroethene, CC12=CHC1, m.p. m 8 6 t o - - 8 7 0 ; b.p. 870; d~5 I "473" n~~ I. 4782 from tetrachloroethane, either by thermal decomposition or by boiling with milk of lime, is largely used for cleaning and extraction purposes but also to some extent as an anaesthetic. On autoxidation it yields dichloroacetyl chloride, but some decomposition to phosgene, carbon monoxide and hydrogen chloride also occurs. Treatment with sodium ethoxide gives the very reactive dichlorovinyl ethyl ether, x,I,2-Tribromoethene, CBr~=CHBr, b.p. 162.5~ d 2~ 2.7o8; n~ 1.6247, is autoxidised to dibromoacetyl bromide. Tetrafluoroethylene, tetrafluoroethene, C2F4, m.p. m I 4 2 . 5 ~ b.p. - - 7 6 . 3 ~ is obtained b y the dechlorination of s-dichlorotetrafluoroethane under pressure (E. G. Locke et al., J. Amer. chem. Soc., I934, 56, I726); the pyrolysis of chlorofluoroform, CHF,C1, (J. D. Park et al., Ind. Eng. Chem., 1947, 39, 354); or by heating sodium perfluoropropionate (L. J. Hals et al., J. Amer. chem. Soc., 1951, 73, 4o54) 9 It is sometimes convenient to prepare it by heating polytetrafluoroethylene ("Teflon", "Fluon") to 6oo-7oo 0 at 15 cm. pressure (E. E. Lewis and M . A . Naylor, ibid., 1947, 69, I968), but when made in this way it always contains hexafluoropropene and octafluoroisobutene. The latter is highly toxic. Tetrafluoroethylene polymerises readily (for methods used and review of physical properties and remarkable chemical stability of the polymer, P.T.F.E. see C. A. Sperati and H. W. Starkweather, Advances in Polymer Science, 1961, 2, 465). Uninhibited tetrafluoroethylene sometimes polymerises violently even below room temperature and the uncontrolled polymerisation can cause explosive degradation to carbon and carbon tetrafluoride. It is therefore essential to avoid storing under pressure unless the vessels are adequately shielded. Since P.T.F.E. is not affected by any known solvents or plasticizers and is not thermoplastic it cannot be processed b y conventional methods. Instead, techniques similar to those of powder metallurgy are used, i.e. the powder is compressed into the shape

520

HALOGENATED ALIPHATIC HYDROCARBONS

3

required and then sintered at about 38o o to allow the particles to coalesce. A co-polymer of tetrafluoroethene with hexafluoropropene is thermoplastic and allows of more conventional handling. Tetrachloroethylene, tetrachloroethene, C~C14, m . p . - - I 9 ~ b.p. 121.2~ d o 1-6558; ~)o 1.5o18 , obtained by treatment of pentachloroethane (addition of chlorine to trichloroethylene) with milk of lime, is used as a solvent and shows no tendency to polymerise. Treatment with ozonised air gives a mixture of phosgene and trichloroacetyl chloride. Tetrabromoahene, C,Br 4, m.p. 56" 50; b.p. 226-227 ~ Tetraiodoethene, C214, m.p. 192~ d 2~ 2.983, is obtained together with s-di-iodoethene by the action of iodine and water on calcium carbide. Chlorotrifluoroethene, CF2=CFC1, m . p . - - I 5 7 . 5 ~ b.p. m27.9~ prepared by the dechlorination of I,I,2-trichlorotrifluoroethane using zinc dust and ethyl alcohol (E. G. Locke et al., J. Amer. chem. Soc., 1934, 56, I726), takes part in the usual free radical, electrophilic and nucleophilic addition reactions (W. If. R. Musgrave, Quart. Reviews, 1954, 8, 331) and is polymerised by irradiation, persulphates and peroxides (C. R. Schildknecht, loc. cir.). Liquid telomers obtained by polymerisation in chloroform solution, have been fluorinated to improve their stability. They find some use as stable lubricants, t h e y and the solid polymers being only slightly less resistant than "Fluon" to heat and to chemical attack. Bromotrifluoroethene, b.p. --6.50/628 mm., prepared by dehydrohalogellating CF2BrCHFBr with potash ill mineral oil (J. D. Park et al., J. Amer. chem. Soc., 1951, 73, 711; and 1956, 78, 59) will polymerise (F. Schlo!Ter and O. Scherer, G.P., 677,o7I/I939) and form a Grignard reagent (H. D. Kaesz, J. Amer. chem. Soc., 196o, 82, 6232). Iodotrifluoroethene, b.p. 28~ mm., n~ 1.4143, prepared from CF~C1CHFI, does not react with the nucleophiles sodium cyanide, potassium orsilver acetates. It forms a Grignard reagent (J. D. Park et al.

loc. cir.).

AUyl halides, CH~:CH.CH~X, are normally prepared from allyl alcohol and hydrogen halides, phosphorus trihalides etc., often in the presence of pyridine to prevent the addition of hydrogen halide to the double bond. A llyl fluoride, b.p. ~ 3 ~ is obtained from silver fluoride and ally1 iodide (M. Meslans, Ann. chim., 1894, I, 374). Allyl chloride, b.p. 450. d~~ 0"9379; n~~ 1"4154, is manufactured by the high temperature chlorination of propylene; in the laboratory it is prepared from concentrated hydrochloric acid and allyl alcohol. Allyl bromide, b.p. 70-7 l~ d~~ 1.398" n~~ 1"4654 (0. Kamm and C. S. Marvel, Org. Synth., Coll. Vol. I, p. 27). The exothermic reaction occurring between allyl bromide and cyclohexylamine has been recommended as a test for an allyl bromide (K.Ziegler et al.,Ann., 1942, 55I, 8o).Altyl iodide, b.p. lO1-1o2~ mm.; d]22 I. 848, is readily prepared from glycerol and hydrogen iodide, or phosphorus and iodine, or from allyl alcohol and hydriodic acid (J. F. Norris, M. Wait and R. Thomas, J. Amer. chem. Soc., 1916, 38, lO71). Homologues of the allyl halides are produced from the corresponding alcohols or by the action of N-bromosuccinimide on the olefins. Many of these higher halides have had important synthetic applications, e.g. the use of I-bromo-3,7,I Itrimethyl-2-dodecene in the synthesis of phytol (F. G. Fischer and K. Lowenberg, Ann., 1929, 475, 183).

2

HALOGENATED

ALKENES

521

Hexafluoropropene, C F 3 C F = C F ,, m.p. --156~ b . p . - - 2 9 . 4 ~ is obtained in excellent yield by heating sodium heptafluorobutyrate (L. J. Hals et al., J. Amer. chem. Soc., 1951, 73, 4054) or by heating tetrafluoroethylene (D. A. Nelson, U.S.P., 2,758,I38/I956) or polytetrafluoroethylene J. S. Waddell, (U.S.P., 2,759,983/I956) to 750o-900 o under reduced pressure. Difluorocarbene, :CF v is formed as an intermediate. Tetrafluoroallene, C F , = C = C F z , b.p.---38~ is prepared as follows: CFg=CH 2 + CF2Brz

> CFzBrCH2CFgBr ~

CF2=CHCF2Br

+ CF2=C=CF ~

(T. L. Jacobs and R. S. Bauer, J. Amer. chem. Soc., 1956, 78, 4815). It polymerises under pressure to give first a liquid and then a white solid and adds chlorine to give tetrachlorotetrafluoropropane. Halogen derivatives of butadiene. For the preparation and properties of various perfluoro-, polyfluoro-, fluorochloro- and other substituted butadienes see J. L. Anderson et al. and R. E. Putnam et al. (ibid., 1961, 83, 382, 386, 389, 391 and by J. D. Park et aI., ibid., 1956, 78, 59). I-Chloro-I,3-butadiene, C H C I = C H . C H - - C H ~ , b.p. 680. d~S o.96o1" n~~ 1.4733 (H. J. Prins, Rec. Tray. chim., 1937, 56 119). 2-Chloro-I,3-butadiene ("Chloroprene"), CH2--CC1.CH=CH ,, b.p. 59"4~ d~~ 0.9583 9 n ~ I. 4583, is formed by the addition of hydrogen chloride to vinylacetylene in presence of copper salts. The primary product is I-chloro-2,3butadiene which rearranges to "Chloroprene" under the experimental conditions. Polychloroprene or "Neoprene" has found wide applications as a synthetic rubber (J. A. Nieuwland and R. Vogt, "The Chemistry of Acetylene", New York, 1946, p. 171 ). The further addition of hydrogen chloride to "Chloroprene" yields 1,3-dichloro-2-butene, CH2C1.CH--CC1.CH 3, b.p. 127-129~ mm.; d~~ 1.4255. As a typical conjugated diene "Chloroprene" may be added to maleic anhydride and other dienophiles in the Diels-Alder reaction: ~CH~ C1. C CH. CO~, ! + II o HC

CH- CO /

"~CH~

/CH2~ C1. C CH--CO~ ~> II I o HC

CH--C0 /

~CH2/

i,i,4,4-Tetrafluorobutadiene C F , = C H - - C H = C F 2 b.p. 4 ~ adds ethyl alcohol in the presence of ethoxide to give a mixture of ethers and olefins which are converted to diethyl succinate on hydrolysis. The use of sodium thiophenoxide in alcohol gives a thioether: CF~=CH--CH=CFz + NaSPh ....EtOH > CFg.= CH--CHgCFg.SPh With peroxytrifluoroacetic acid, fumaric acid is formed, possibly via 1,4-addition of hydroxyl radicals (Anderson et al., Ioc. cir.):

522

HALOGENATED ALIPHATIC HYDROCARBONS

3

HC---C0~H CF2=CH--CH=CF t ---+ [HOCF2--CH =CH--CFtOH ]

9

II

H0,C--CH Heating produces a dimer, trimer, and higher polymers free radical or u.v. initiation leads to the formation of high molecular weight polymers (Putman

et al., loc. cir.) Hexafluorobutadiene, C F , = C F - - C F = C F 8, b.p. 5.8 ~ can also be prepared from CF~=CFC1 by adding iodine monochloride, coupling, and dechlorinating the resultant 1,2,3,4-tetrachlorohexafluorobutane (R. N. Haszeldine, J. chem. Soc., 1952, 4423). It, and other perfluorodienes, isomerise on heating with caesium fluoride to perfluoroalkylacetylenes (W. T. Miller et at., J. Amer. chem. Soc., 1951, 83 I767): CF~=CF--CF--CF 2 ~

CF3~C--CF

~

I, 1,2,3,4,4-Hexachlorobutadiene ("Tripene"; "Perchloromesole") is frequently obtained as an end product in exhaustive chlorinations and is prepared technically from trichloroethylene as follows: heat at

heat with

CHCI=CCI9 2xoo/4oats. > CC12=CH'CHCI'CC18 FeCltatzzo ~

CCI~=CH-CCI=CCI~

boil with Cl,_.+ CC13.CHC1.CCI__CC12 Fe ~tngs/I-I,O > CC12"-CCI'CCI=CC12

It is used as a solvent.

3. Halogen derivatives of the acetylenes; halogenoalkynes

(i) Preparation (I) From a metallic derivative of an alkyne and a halogen (T. H. Vaughn and J. A. Nieuwland, J. Amer. chem. Soc. 1932, 54, 7 8 7 ) o r an arylsulphonyl chloride (R. Truchet, Ann. chim., 1931, 16, 309): liq. NH,

N a ~ C N a + 12 orC.H. > CI~---CI R~CNa

+

PhSO~C1

>

R~CC1

+

PhSO2Na

(2) By removal of hydrogen halide or halogen from a halogenated alkene or alkane (E. Ott, Ber., 1942 , 75, 1517; R. N. Haszeldine, J. chem. Soc., 1951, 588; 1952, 25o4; A. L. Henne and W. G. Finnegan, J. Amer. chem. Soc., 1949, 7I, 298; C. G. Krespan et al., ibid., 1961, 83, 3424):

2

HALOGENATED ACETYLENES CCI~.--CHCI CF3CH =CHI

523

> CCI~-~-CCI ---+ CF3~---CH Zn

C1CF2CF~CC1=CC1CFzCF~-C1 Ac,O > C1CFaCFg-C~CCFg-CFaC1

(3) By treating acetylenic acids with sulphur tetral~uoride (W.R. Hasek et al., ibid., 196o, 82, 543). (4) For perfluoroalkylacetylenes, by heating per~uorodienes with caesium fluoride (W. T. Miller et al., ibid., 1961, 83, 1767)" CF~---CF~CF=CF2

x5o~

CsF ~ CF3~CCF3

This is a general reaction of perfluorodienes and results from a series of S•2' substitutions with fluoride ion. (5) By the action of phos1~horus halides on acetylenic alcohols: 3CH~C--CHgOH + PC13

-> 3CH~C---CHg.C1 + H3PO 3

(6) For co-fluoroalkylacetylenes from a sodium acetylide and an o~-bromoco-~uoroalkane (F. L. M. Pattison and J. J. Norman, ibid., 1957, 79, 2311): F(CH2)sBr + N a ~ C H

> F(CHz)s~CH

Alternatively the corresponding co-dichloro-compound can first be reacted with potassium fluoride in ethylene or diethylene glycol. (7) By pyrolysis of halogeno(l~uoro)maleic anhydrides (W.J. Middleton and W. H. Sharkey, ibid., 1959, 81,803): FCuCO~

I[

o -- > CF-----CH+ CO,. + CO

HC--CO /

For syntheses and reactions of monohalogenoacetylenes see T. L. Jacobs (Org. Reactions, 1949, 5, I) and R. A. Raphael ("Acetylenic Compounds in Organic Synthesis", Butterworths, London, 1955).

(it) Properties and reactions Halogenated acetylenes are unstable to varying degrees and must be handled with great care but in most cases reactions can be carried out in inert solvents. Their instability may be due to spontaneous exothermic

524

HALOGENATED ALIPHATIC HYDROCARBONS

3

polymerisation; in some cases this can be regulated and halogenated benzenes, as well as compounds of higher molecular weight, are produced. The halogen atom is very resistant to nucleophilic substitution and it is doubtful whether any of these reactions, except those with alkali metals to give the metal acetylides, involve a direct replacement of the halogen atom. It is much more likely that the first step involves addition of the reagent across the triple bond followed by elimination of hydrogen halide: C1C-~CC1 + N H a

> C1CH =C(NH2)C1 CI~CNH 2

> C1C-7----CNHg.+ NH4C1

> CH2C1--C~N

The monohalogenoacetylenes have an acidic hydrogen atom which can be replaced by metals as in the case of acetylene itself. Of the halogenoalkylacetylenes the proJmrgyl halides are well known (cf. p. 525); they resemble allyl halides in that the halogen atoms are highly reactive to nucleophilic reagents but differ in that they do not undergo anionotropic rearrangements. For review see A. W. Johnson ("The Acetylenic Alcohols", Arnold, London, 1946, 62) and Raphael (loc. cir.). The perfluoroalkylacetylenes have been investigated in considerable detail. In them tile triple bond is very reactive and will undergo free radical (K. Leedham and R. N. Haszeldine, J. chem. Soc., 1954, I634), electrophilic and nucleophilic addition reactions (A. L. Henne and M. Nager, J. Amer. chem. Soc., 1952, 74, 650; R. N. Haszeldine, B.P., 772,IO9-IO/I957) : CF3I + C F 3 C ~ C H HBr + CF3~--CH C2HsOH + C F 3 ~ C H HgO + C F 3 ~ C H

HgS~

~ CF3CI=CHCF 3 > CF3CH--CHBr NaOEt > CF3C H = C H O E t CF3CHgCHO + CF3COCH 3

These reactions occur very easily and stop when one molecule of reagent has been added. The hydrogen atom in trifluoromethylacetylene is acidic and copper, silver and mercury derivatives are formed. It also reacts with Grignard reagents: CzHsMgBr + C F 3 ~ C H

L > CzH 6 + C F 3 ~ C M g B r

The bis-(perfluoroalkyl)- and bis-(fluorochloroalkyl)-acetylenes are very active dienoptliles and in addition to adding to butadiene"

3

525

HALOGENATED ACETYLENES

-.~/CF3

CF3--~C,--CF 3 + CH2--CH--CH=CH 2

"f U ,

they will add 1,4 to durene and naphthalene to give bicyclo-octatrienes (R. E. Putnam et al., J. Amer. chem. Soc., 1961, 83, 391):

iF3

F.3CJ(F F3

C

CH3~CH3

C

CH~

J CF~

~

CH3,,.-;;--~//_~C CH 3

H3

CH3

They are sufficiently reactive even to add to benzene but the temperature required to cause reaction is above the decomposition point of the bicyclooctatriene formed and a number of poly(trifluoromethyl)-benzenes and -naphthalenes are isolated (C. G. Kres#an et al., J. Amer. chem. Soc., 1961, 83, 3428). Bis-(polyfluoroalkyl)-acetylenes also react with elemental phosphorus to give diphosphabicyclo-octatrienes while their di-iodides react with arsenic to give the corresponding diarsenabicyclo-octatrienes (loc. cit., p. 3432). With sulphur they give dithietenes and with selenium, diselenins.

(iii) Individual compounds Fluoroacetylene, CF=CH, m.p. N --i960, b.p. N --8o 0, prepared quantitatively by heating monofluoromaleic anhydride at 650~ ram., is not spontaneously inflammable in air. Liquid samples are liable to explode but the gas appears to be stable. It slowly condenses to 1,2,4-trifluorobenzene and a yellow-brown polymer. A pyrophoric reaction occurs with bromine in carbon tetrachloride giving mainly CHBr~CBr2F. Silver and mercury salts are formed; both decompose violently on warming. Difluoroacetylene, CF-----CF, a gas obtained together with its cream coloured, solid dimer by heating difluoromaleic anhydride at 65o~ mm., polymerises rapidly at room temperature. With water or alcohols it gives polymers containing carboxy or carbalkoxy groups (W. J. Middleton, U.S.P., 2,831,835/1958). Chloroacetylene CCI~CH, first obtained from dichloroacrylic acid, CC12--CH-CO2H, and barium hydroxide (0. Wallach, Ann., 188o, 23o, 88), is also obtained from 1,2-dichloroethylene by warming with mercuric cyanide and potassium hydroxide (L. A. Bash[oral, H. J. Emeldus and H. V. A. Briscoe, J. chem. Soc., 1938, 1358). It is a poisonous gas which explodes spontaneously in air (E. Ingold, ibid., 1924, x25, 15351. Ammoniacal solutions of silver or copper salts yield explosive precipitates and an aqueous solution generates ozone and

526

HALOGENATED ALIPHATIC HYDROCARBONS

3

glows in the dark. The insoluble mercury derivative has been used as a means of purification (K. A. Ho]mann and H. Kirmreuther, Bet., 19o9, 42, 4232). 1,3,5-Trichlorobenzene has been isolated from the products of polymerisation. Dichtoroacetylene, CCI~CC1, m.p. m 6 6 ~ to m 6 4 . 2 ~ b.p. 32-33~ mm.; d~~ 1.261" n~~ 1.4279, prepared by passing trichloroethylene at 13~ over potassium hydroxide (Ott, loc. cir.) or by the action of acetylene on alkaline potassium hypochlorite solution ill an atmosphere of nitrogen (F. Straus, L. Kollek and W. Heyn, Ber., 193 o, 63, i868), explodes violently in presence of a trace of oxygen but can be conveniently kept as a dilute ethereal solution. For the reactions see E. Ottet al., Ber., 1943, 76, 80, 84, 88. Bromoacetylene, CH~-CBr, a poisonous gas, b.p. u 2 ~ burning with a purple flame, is polymerised in sunlight to 1,3,5-tribromobenzene among other products. Dibromoacetylene, CBr~CBr, m.p. ~ 2 5 ~ t o - - 2 3 ~ b.p. 76~ d 2.o, from tribromoethylene by the action of alcoholic potassium hydroxide or b y the action of alkaline potassium hypobromite on acetylene, is spontaneously inflammable and explodes on heating. Iodoacetylene, CH--CI, b.p. 320 (V. Grignard and K. Tcheou[aki, Compt. rend., 1929, z88, 357). Di-iodoacetylene, c I - c I , a yellow crystalline solid, m.p. 81-820 (dec.), obtained by the action of iodine on a metallic derivative of acetylene or from sodium hypoiodite and acetylene (T. H. Vaughn and J. A. Nieuwland, J. Amer. chem. Soc., 1932, 54, 788), is relatively stable in air but slowly decomposes ill light to form tetraiodoethylene and carbon. It forms molecular compounds with amines e.g. N E t s, 2Crib, and reacts with phenylhydrazine to give I-phenyl-2-iodoacetylene (W. M. Dehn, ibid., 1911, 33, 1598). Propargyl halides. Propargyl chloride. CH-~CCH~C1, b.p. 65 ~ d 5 1.o454 bromide, b.p. 88-9 o~ d 1~ 1"579, nb 9 1-4942. r e.g. ?-fluoropentyne, F(CHj)sC=---CH, from ~-bromo?-fluoropropane and sodium acetylide (F. L. M. Pattison and J. J. Norman, ibid., 1957, 79, 2311) 9 Perhalogenoalkylacetylenes, I,I,I-Trifluoropropyne, C F s C ~ C H , b.p. w48~ from acetylene and trifluoromethyl iodide. Hexafluoro-2-butyne, CFsC mCCF 3, b.p. --24 ~ from acetylene dicarboxylic acid and sulphur fluoride, or by dehalogenating 2,3-dichlorohexafluoro-2-butene (C. I. Gochenauer, U.S.P., 2,546,997/ 1951 ) with zinc and ethyl alcohol. In addition to the reactions already described it will trimerise to hexa(trifluoromethyl) benzene. I, 6-Dichloro-octafluoro-3-hexyne, CC1FsCFtC-~CCFsCC1F s, b.p. 82-84 ~ n~r 1.32IO, by dehalogenating 1,3,4,6tetrachloro-octafluoro-3-hexene.