Free radical chemistry. Part 6[1]. Halogenation of polyfluoro-ethers and -borate esters

Free radical chemistry. Part 6[1]. Halogenation of polyfluoro-ethers and -borate esters

Journal of Fluorine Chemistry, 30 (1985) 22-l 227-235 Received: April 16, 1985; accepted: July 28, 1985 FREE RADICAL -BORATE HALOGENATION PART 6...

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Journal of Fluorine Chemistry, 30 (1985)

22-l

227-235

Received: April 16, 1985; accepted: July 28, 1985

FREE RADICAL -BORATE

HALOGENATION

PART 6[11.

OF POLYFLUORO-ETHERS

AND

ESTERS

R.D. CHAMBERS

Department Durham

CHEMISTRY.

and B. GRIEVSON

of Chemistry,

University

Science

Laboratories,

South Road,

City, DHl 3LE (U.K.)

SUMMARY

Chlorination results

and bromination

of CH30CH2CF2CFHCF3

for the site of halogenation

lateness

of the transition-state

supports

the theory.

a new route for conversion

and a rationalisation

is advanced.

Chlorination

gave contrasting

Direct

of fluorinated

of fluorinated

alkenes

based on the

fluorination

trialkylborates to fluorinated

provides acid

chlorides.

INTRODUCTION

In earlier parts of this series we described dimethylether

121 and trimethylborate

we are exploring We

alkenes.

the chemistry

studied

(2) was obtained

free-radical

[3] to various

additions

fluorinated

alkenes

of and

of these and other adducts to fluorinated

[2] chlorinations

and bromination

using bromine but chlorination

of (1) and found that

products

were very solvent

dependent.

a

H

H

H CH20CH3

(1)

CHXOCH3

a

(2)

F

+

F

F

CH20CH2X

o(3)

(X = halogen)

0022-l 139/85/$3.30

0 Elsevier Sequoia/Printed

in The Netherlands

228 RESULTS

AND DISCUSSION

In the light of the puzzling have now explored

results

the corresponding

obtained

halogenation

the product

obtained

of these studies are shown below and a preference

position

CF3CFHCF2CH20CH3

of dimethylether

with

The results terminal

from addition

in halogenation

reactions

hv,

+ Cl2

to hexafluoropropene.

In contrast,

is clearly observed.

CF3CFHCF2CHClOCH3

reaction

(6) + CF3CFHCF2CHC10CH2C1

+ CF3CFHCF2CH20CHC12 (7) Solvent

% (5)

Neat ccl4 cs2

(8)

L(7) + (a)1

(6)

6

45

47

4

49

45

16

76

7

not only differed

bromine,

through

the preference

for the position

halogenation

but, also, in the fact that substantial

dimerisation

products

(4) + Br

Sunlight 2

3

for the of (4) with

+ CF3CFHCF2CH20CH2Cl

(5)

(4)

of (1) w

(4) i.e.

It is clear, however,

were obtained.

CF3CFHCF2CHBrOCH3

of

amounts of dehydrothat although

+ CF3CFHCF2CH20H (10)

(9) + Dehydrodimers (11) Solvent

% (9)

Neat cs2 chlorination

(10)

(11)

12

38

49

81

9

9

occurs preferentially

occurs preferentially An explanation reactivity

at the internal

whereas

CH

of bromine

and chlorine

lower reactivity

[4].

bromination

lies in the relative

atoms and the consequences

postulate

with a transition-state

position,

site.

2 for these contrasting results

that stem from the Hammond reactivity

at the terminal

This approach

that resembles

would be associated

of this,

associates

greater

the initial state,

with a transition-state

closer

229

In the present

to the product.

could be represented

context,

of halogenation,

by transition-states

these situations

(12) and (13) and the consequence

of this would be that polar effects would be more important the stability

of the developing

for (12) while

radical would be more important

+

product

*

product

for (13).

’ (13) In comparing

chlorination

state for chlorination of the transition-state preferential consistent

and bromination,

it is likely that the transition-

is more like (12) and, for bromination, will move

attack of a chlorine

towards

the character

On this basis,

(13).

atom at the terminal position

with a transition-state

like (14) because

the

in (4) is

this involves

attack at

H3C-0 [CF~CFHCF~+-

[CF,CFHCF,CH,O-CH,-H----cY]

(15)

(14)

the least electrophilic group would

I%H----cl*]

inhibit formation by

be even less likely, transition-state

Electron

site.

withdrawal

of (15), while attack at the CF3CFH-site

the electrophilic

chlorine

like (13) for attack by bromine,

that (16) is preferred would be stabilised

by the polyfluoroalkyl

to (17).

by adjacent

Although oxygen

atom.

Assuming

would

a

then we can appreciate

both of these transition-states

(la), nevertheless,

(16) is preferred

CH 01 [CF3CFHCFz&----H-Br]

iCF,CFHCF,CH,'d-tH,---H-Brl

(16)

(17)

as a developing radical

E-?-R

(17).

(or RF)

secondary Although

W

-z

?&O-R

(or RF)

primary

atom at the CF3CFH site would

R = alkyl RF = Polyfluoroalkyl

1

(lab)

lead to a developing obviously

rather than the developing

attack by a bromine

(Ma)

oxygen

radical,

tertiary

less favourable

[5,6j.

radical

in the transition-state,

than the known stabilising

influence

this is of adjacent

230 A consequence fluorine chlorine. through

of this model for reactivity,

We have tested this by bubbling

a solution

of (4) in CF2ClCFC12,

products

(19) - (21) arise wholly

together

with a small amount of alcohol

induced

(4)

is that attack by a

atom on (4) should be even more governed

cleavage

F2, N2 CF2C1CFC12,

at room temperature

(10) probably

and the

arising

of (21) probably

CF3CFHCF2CH20CH2F

R.T.'

diluted with nitrogen,

from attack at the terminal position,

The formation

of (4).

by polar effects than

fluorine,

from acid-

partly arises from

(44%)

(19) + CF3CFHCF2CH20CHF2

(18%)

(20) + CF3CFHCF2CH20COH

(20%)

(21) + CF3CFHCF2CH20H

(7%)

(10) the presence

of oxygen impurity

of hydrocarbon

by other workers

shown

to fluorinated

corresponding

+

oxygen, has been reported

[3] that free-radical

alkenes,

fluorinated

e.g. (RCH~~)~B

since the functionalisatior

containing

[7,81.

We have recently borates

in the fluorine,

groups, using fluorine

cF2=cFcF

occurs readily,

trialkylborates

additions

of trialkyl-

to give high yields

(22).

of

These derivatives

Y or 3

Peroxide'

(RyH0)3B CF2CFHCF3 (22)

are readily

chlorinated

fluorinated

alkenes

and,overall,this

to corresponding

provides

a route for conversion

acid chlorides

of

(23) (see Table).

F-alkene--~(Cl)H-~-~_C0C~ (23)

Earlier adducts

’ ’

workers

have described

but these reactions

containing

usually

chlorination

of corresponding

gave complex mixtures

little or none of the acid chloride

[9,10].

methanol

of products,

231 TABLE Chlorination

of fluorinated

trialkylboratesa % Yield

AcidChloride

Borate

CF3CFHCF2COCl

B(OCH2CF2CFHCF3)3

(2)

75

(28)

83

(29)

63

COCl

F

H

0:

COCl F

Cl

[7

(a) Sealed pyrex tube, excess chlorine,

UV irradiation,

18 - 50°C.

EXPERIMENTAL

The radical

induced addition

alkenes used as starting paper

Chlorine

[3J.

by normal vacuum

products

materials

was used as supplied

line techniques.

of ethers and borates

were prepared

as outlined

and transferred

Quantitative

analyses

carried

out on a Varian 'Aerograph Model 920 equipped

balance

detector

instrument purify

(di-isodecylphthalate

equipped

the products.

Varian EM360L chemical

by glc were

with a gas density P).

with a cold trap for sample collection

spectrometer

operating

shifts are quoted relative

fluoromethane.

from the cylinder

20%, on chromosorb

Proton and fluorine

A similar

was used to

nmr spectra were recorded

on a

at 60 and 56.46 MHz respectively to tetramethylsilane

Mass spectra were recorded

and glc/ms were recorded

to fluoro-

in a previous

and

and trichloro-

on an A.E.I. MS9 spectrometer

on a V.G. Micromass

12B spectrometer

fitted with

a Pye 104 glc.

Chlorination

(a)

of 2,2,3,4,4,4-hexafluorobutylmethyl

ether (4)

Neat

Adduct

(4) (1.95 g, 10 mmol),

tap, was degassed transfer. disappeared

and chlorine

contained

The mixture was left in sunlight (5 30 mins.).

in a Pyrex tube with

(0.7 g, 10 mmol) introduced

'rotaflo'

by vacuum

until the chlorine

colour

The tap was opened and the gaseous products

232 c

vented

to give a liquid product

Separation

(2.49 g).

gave l-chloro-2,2,3,4,4,4_hexafluorobutyl

by preparative

glc

methyl ether (5) (0.14 g, 6%) (nc);

6H 3.78 (3H, s, CH3), 5.77 (IH, t (broad), CHF), 6F 74.2, 74.6 (3F, m, CF3), 122.4, 124.0, 124.7 (2F, m, CF2), and 214.9, 216.0 79(36),

m/z 195 (Mf-Cl, 12), 81(14), methyl

ether

(5) (1.10 g, 45%) (nc), b.p. 133OC (Found: C5H5C1F60

Cl, 15.7.

F, 48.5;

(lF, dm, J 44 Hz, CFH);

2,2,3,4,4,4_hexafluorobutyl C, 26.4;

H, 2.2;

C, 26.0;

requires:

chloroH, 2.3;

F, 49.5;

Cl,

15.4%);

6H 4.13 (2H, m, CH2CF2), 5.10 (lH, dm, J 44 Hz, CFH), 5.63 (2H, s,

0CH2C1),

6F 75.0 (3F, m, CF~), 117.3, 122.0 (2~, AB, J 221 Hz, CF2), and

214.3

(lF, dm, J 44 Hz, CFH);

49(100),

and a mixture

(Found:

C, 23.0;

22.6;

H, 1.5;

m/z 195 (M+-Cl, 45), 81(32),

of di-chlorinated F, 41.1;

H, 1.8;

F, 43.0;

Cl, 26.8%);

CFH) (3.8 H), 5.70 (a.6 H, s, 0CH2C1),

(b)

Carbon tetrachloride

A mixture

containing

equipped gaseous

with a rotaflo by-products

comparison

?iH4.37

(1) and (8) (1.14 g, 47%) C5H4C12F60 CF2CH20)

(m,

requires:

C,

and 5.10 (dm,

7.48 (lH, s, OcHC12).

(4) (0.99 g, 5 mmol), chlorine

(3.11 g, 20 mmol), contained

tap was irradiated

were allowed

of glc retention

51(66),

solvent

adduct

mmol) and carbon tetrachloride

species

Cl, 26.9.

79(97),

with sunlight

to evaporate

(0.51 g, 7

in a pyrex tube

for 1 hour.

The

leaving a liquid product

times with port (a) gave the chlorinated

and

adducts

(2) (4%), (5) (49%) and (I) and (8) (45%).

(c)

Carbon disulphide

A mixture

containing

solvent

adduct

6 mmol) and carbon disulphide for one hour.

The gaseous

a liquid product (Z)PlUS

(a)

adducts

to evaporate

leaving

(5) (16%), (2) (76%) and

methyl

ether (2)

Neat containing

13 mmol) contained

adduct

(4) (1.94 g, 10 mmol) and bromine

in a pyrex tube with a rotaflo

for 3 days. to evaporate

components ether

were allowed

the chlorinated

of 2,2,3,4,4,4_hexafluorobutyl

A mixture

allowed

by-products

containing

(0.45 g, with sunlight

(8) (7%).

Bromination

sunlight

(4) (1.04 g, 5 mmol), chlorine

(2.81 g, 37 mmol) was irradiated

The tube was opened to leave a yellow

by preparative

(2.04 g,

tap was irradiated

and the gaseous by-products

liquid

(2.7 g).

Separation

C, 22.1;

were

of the

glc gave l-bromo-2,2,3,4,4,4_hexafluorobutyl

(z), (0.32 g, 12%) (nc), b.p. 134OC (Found:

with

H, 1.8;

methyl F,

233

41.7;

Br, 29.7.

C5H5BrF60

requires:

C, 21.8;

H, 1.8;

F, 41.5;

Br,

6H 3.63 (3H, s, CH3), 5.27 (lH, dm, J 44 Hz, CHF), 6.00 and 6.07

29.1%);

(lH, t, J 9 Hz, CHBr);

Q

m, CF2), 215.3 and 217.3

76.1 and 76.7 (3F, m, CF3), 120.1 and 122.1 (lF, dm, J 44 Hz, CFH);

2,2,3,4,4,4-hexafluorobutan-l-o1 dehydrodimers

(2)

(2)

(1.32 g, 49%),

(2F,

m/z 195 (M+-Br, lOO%),

[ll] (1.02 g, 38%), and unassigned

(Found:

F, 58.8.

C10H10F1202

requires:

F, 58.5%), m/z 195 (100%).

(b)

Carbon disulphide

A mixture

containing

solvent

adduct

0.75 mmol) and carbon disulphide light for 72 hours. to evaporate

(4) (0.3 g, 1.5 mmol), bromine

(2.78 g, 37 mmol) was irradiated

The tube was opened and the gaseous

to leave a liquid containing

(9%). assigned

by comparison

(0.12 g, with sun-

by-products

allowed

(2) (81%), (lo) (9%) and (2)

of glc retention

times with authentic

samples

from part (a).

Fluorination

of 2,2,3,4,4,4-hexafluorobutyl

A mixture

containing

adduct

chloro-1,2,2_trifluoroethane with a reflux condenser a nitrogen ml/min.) period) 10 mins. ether 4.80

cylinder

was passed and finally

(55 g) was placed

fluorine

for 10 mins. then fluorine

(18%) (Found:

generator.

contained

(50 ml/min.)

2,2,3,4,4,4_hexafluorobutyl 4.36

Nitrogen

(50

(0.48 g over a 22 min.

flushed out with a flow of nitrogen

for

fluoromethyl

(2H, d, J 55 Hz, CH2F),

6F 76.2 (3F, m, CF3), 118.9, 123.0 (2F, AB, J 277 Hz,

CF2), 155.7 (lF, t, J 54 Hz, CH2F), 215.7 CM+-H, l%), 63(100),

in a Pyrex flask assembled

and an inlet tube attached via a three way valve to

and an electrolytic

The product

(4)

(2) (2.46 g, 12.5 mmol) and 1,1,2-tri-

(19) (44%), 6H 3.17 (2H, m, CH2CF2), (lH, m, CHF);

methyl ether

(lF, dm, J 44 Hz, CFH);

2,2,3,4,4,4-hexafluorobutyl

C, 26.1;

H, 1.9.

C5H4F80

difluoromethyl

requires:

C, 25.9;

m/z 213

ether

(20)

H, 1.7%);

6H 4.52

(2H, m, CH2), 5.23 (lH, d, J 45 Hz, CHF), 6.55 (lH, t, J 73 Hz,

CHF2);

6F 76.3 (3F, m, CF3), 88.4 (2F, d, J 71 Hz, CF2H), 120.9

CF2CH2), (1)

215.7

(lF, d, J 43 Hz, CFH), 2,2,3,4,4,4_hexafluorobutyl

[3] (20%), and 2,2,3,4,4,4-hexafluorobutan-l-01

(lo)

[III

(2F, m, formate

(7%).

234 Chlorination

(a)

of borate adducts

Tri(2,2,3,4,4,4-hexafluorobutyl)borate

A mixture

of borate

contained

mmol),

and irradiated

(with a temperature leaving

with a high pressure The gaseous

rise to 5O'C).

22.4;

(6.61 g, 93

C, 22.4; H, 0.5;

UV lamp for 1 hour

by-products

a liquid residue which was transferred

18OC to give 2,2,3,4,4,4_hexafluorobutanoyl (Found:

(24) and chlorine

in a thick pyrex tube fitted with a rotaflo valve, was

sealed under vacuum

evaporate

(0.97 g, 1 mmol)

(3)

under vacuum at

requires:

6h 5.08 (dm, J 44 Hz, CFH);

F, 53.1%);

Cl, 16.5;

to

(27) (0.85 g, 75%) (nc)

C4HC1F60

F, 49.8.

Cl, 16.1;

H, 0.7;

chloride

were allowed

C, 6F 76.0

(3F, m, CF3), 112.3, 117.1 (2F, AB, J 278 Hz, CF2), 214.2 (IF, dm, J 42 Hz, CFH);

m/z 213 CM+-H, l%), 151(58),

(b)

65(32), 63(100).

Tri[(1,2,3,3,4,4,5,5,6,6-decafluorocyclohexyl)methyl~borate

A mixture mmol),

69(95),

of borate

contained

(5)

(0.68 g, 0.8 mmol) and chlorine

and irradiated

(with a temperature

rise to 50°C).

and the remaining

with a high pressure The gaseous

59.4.

(mixture of isomers) C7HClF100

5.32 (m, CHF); 179.3

requires:

(Found: C, 25.7;

(c)

of borate

contained

temperature evaporate

(28) (0.62

H, 0.0%;

Cl, 13.4;

F,

Cl, 10.9;

F, 58.2%),

6H

AB, 4CF2), 167.5 and

(lF, dm, J 42 Hz, CFH);

m/z 291 (M'-Cl,

borate

and irradiated rise to 5OOC).

and the remaining

with a high pressure The gaseous

liquid was transferred methanoyl C5C12F60

6F 126.8

F, 44.4.

CF2), 136.2 and 141.4 CM+-Cl, 14%), 225(48),

chloride

147(68),

to

(29) (nc) (0.73 g, C, 23.0;

(2F, AB, J 214 Hz,

(lF, m, CF), 159.0 and 168.1 149(21),

were allowed

under vacuum at 18'C to

requires:

(2F, m, CF2), 122.6, 131.4

(10.34 g, 146 tap, was sealed

UV lamp for 1 hour (with a

by-products

give 3-chlorohexafluorocyclobutyl C, 22.3;

(26)

(26) (0.75 g, 1.3 mmol) and chlorine

in a thick Pyrex tube fitted with a rotaflo

63%) (Found: F, 43.7%);

chloride

Tri (1,2,3,3,4,4-hexafluorocyclobutyl)methyl

under vacuum

to

63(100).

A mixture mmol),

were allowed

under vacuum at 18'C to

hF 118.1 to 149.8 (8F, overlapping

(lF, m, CF), 210.0 and 229.3

15%), 65(56),

C, 25.9; H, 0.3;

UV lamp for 2 hours

by-products

liquid was transferred

give 1,2,3,3,4,4,5,5,6,6-decafluorocyclohexylmethanoyl g, 83%)

(6.06 g, 85

in a thick Pyrex tube fitted with a rotaflo tap, was

sealed under vacuum

evaporate

(25)

118(31),

(lF, m, CFH); 116(100),

m/z 227

65(26), 63(82).

235 ACKNOWLEDGEMENT We thank the Science maintenance

grant

and Engineering

Research

Council

for a

(to B.G.).

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Part 5.

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