Coulometric titration of deactivated phenols with bromine

1042

SHORT COMMUNICATIONS

Table 1 Uranmm content of two U S Geological Survey standard rocks

Standard rock Dumte DTS-1

Present work Smgle Mean values, value, PPM

PPM

32 6, 3,23 4. 8,

30

28 Perldotlte PCC-1

Lrterature values,

The hmrt of detectron of thus method wrth the neutron flux and measurement condmons used m the present work IS about 0 2 ng of uramum If necessary, a sample stze of 500 mg could be used, thus permtttmg uramum conconcentratrons at the 0 5 ppM level to be determmed

PPM

REFERENCES

;;;1:;;::

; E Stemnes and D Brune, Talanm, 1969, 16, 1326 A 0 Brunfelt and E Stemnes, Anal Chrm Acta, 1969, 48, 13 E I Hamdton, Earth Planet SCI Letters, 1966, 1, 317 : N H Gale, Proc I A E A Symp Radroactnx Dattng and Methods of Low-level Countmg, Vienna, 1967, p

40’154;6

4 6,4 0, 40,33, 37

39

5.+ 4 7,5 41,s47,r1 49,‘s 5 l6

431

5 D E Frsher, Anal Chem 1970, 42, 414 6 H Wakrta, H Nagasawa, S Uyeda and H Kuno, Earth Planet. SCI Letters, 1967, 2, 377

work are m espectally good agreement wrth those of Morgan and Herer,’ who also used a radlochemrcal method based on the 238U (n,r) reaction The precrsron of the method appears to be about + 10% when the amount of uranmm determined 1s about 1 ng The radronuclidrc purrty of the separated sample appeared to be satrsfactory, as all the malor actrvmes, such as 56Mn and *‘Mg, appeared to have been effictently removed The only forergn activity present m srgmficant amounts appeared to be lc5Dy In samples wrth higher concentrahons of the heavy rare-earth fractton or wrth a more unfavourable U/Dy ratio rt IS recommended that another 2 or 3 washmg steps with 5M mtrtc acid be Introduced Each of these steps would reduce the dysprosium concentratton by about a factor of 3, whrle the uranmm concentrations would probably not be reduced by more than 2%

7 J W Morgan and J F Lovermg, Anal Chum Acta, 1963, u), 405 8 J W Morgan and K S Herer, Earth Planet Scr Letters, 1966, 1, 158 9 M Sankar Das, US At Energy Comm Rept TID18204, 1962 10 C Turkowsky, H Stark and H J Born, Radlochzm Acta, 1967, 8, 27

11 P J Aruscavage and H T Mrllard, J Radzoanal Chem, 1972, 11, 67 12 E Stemnes, Radwchem Radloanal Letters, 1973, 16, 25

13 E Stemnes, Anal Chrm Acta, m the press 14 S Sterlmskr, Anal Chem, 1968, 40, 1995 15 H Hamaguchr and N Onuma, crted m F J Flanagan, Geochlm Cosmochlm Acta, 1969, 33, 81

16 S Nrshrmura, Chem Geology, 1969/1970, 5, 139

Summary-A radrochemtcal neutron-actrvatron method for the determmatron of trace concentratrons of uranmm m rocks IS descrrbed The method 1s based on separation of 23 5-mm 23vU after alkaline fusron by extraction with trr-n-butyl phosphate from moderately concentrated mtrrc acid, followed by measurement of the 74-keV y-ray wrth a Ge(Lr) detector The hmrt of detectron IS D2ng of U under the present condmons, and the precrsron at the 0005 ppm level IS about loO/, The method IS especially useful for determmatron of uramum m ultramatic rocks

ralnnta,Vol

22, pp 1042-1045 Pergamon Press 1975 Pnnted m Great Bntaln

COULOMETRIC

B

TITRATION

KINBERGER,

L

OF DEACTIVATED BROMINE

E

EDHOLM

PHENOLS WITH

and B E F SWTH@

Department of Technical Analytical Chemistry, Chemical Center, Lund, Sweden (Recerved 17 March 1975 Accepted 28 March 1975)

In a previous paper’ a general method for coulometrrc trtratron of alkylphenols wrth anodrcally generated bromme was descrrbed The present paper deals with coulometrrc brommatron of deactivated phenols The coulometrrc brommatron method has httherto been applied only to a small number of deactivated phenols Lrchtenstem’

titrated 4-chloro-3,5-drmethylphenol and 2,4-dwhloro-3,5drmethylphenol m aqueous solutron which was 0 2M wrth respect to potassium bromide and 1M wrth respect to sulphurrc acid One hydrogen atom was exchanged for bromme Delgado’ titrated sahcyhc acrd and 2- and Cmtrophenol at pH 3 m aqueous solutton whrch was 02M wrth

SHORT COMMUNICATIONS

respect to potassium bromide Two hydrogen atoms were exchanged for bromine m tl-ns case Although our previous work’ m this series dealt with activated phenols, conclusions concerning suitable condotions for the coulometrtc biommation of deactivated phenols can nevertheless be drawn Monobrommation was found to dominate m pyndme-free acetic acid-water media while full brommation mainly occurred m pyndme-contaming media As the latter reactlon mvolves brommatlon of a bromophenol as an intermediate product, I e , a deactlvated phenol, it can be concluded thatebrommated phenols require pyridme-acetic acid-water media for quantitative brommatlon * The same was found to be the case for all fully deactivated phenols titrated m this work The term “deactivated phenol” 1s often interpreted as meamng any phenol containing electron-withdrawing groups such as mentioned m the summary A method of determining the relative degree of activation of phenols may be based on reaction with an electrophllic reagent such as bromine A test for this purpose IS described later m this paper It should be noted that accordmg to this test, some of the phenols investigated here are activated The effects of various factors on the brommatlon reaction were reported m the previous paper 1

1043

Fig 1 Shape of titration curves obtained m the test for distmgmshmg activated and deactivated phenols A = activated phenols, B = fully deactivated phenols, C = partly deactivated phenols

on reaction with bromine m medmm III-l, will give a type B titration curve Accordmgly they will be classtied as fully deactivated regardless of then activation state

EXPERIMENTAL.

apparatus as well as the reagents used were the same as those described earher ’ All phenols were of the best grade commercially available and they were generally analysed without further purfication The standard titration procedure was identical with that used before,’ I e, a generating current of 3 mA at a 2-cm2 Pt-electrode, and a polarlzmg voltage of 630mV through a lOOkQ resistance were used The chart speed was 30 mm/nun The composition of the titration media was shown m Table 1 of the earlier paper 1 The

RESULTS AND DISCUSSION

Dutmguuhmg

between actwated and deactrvated phenols

The authors are not aware of any previous method which dlscrlmmates between activated and deactivated phenols The test proposed here IS based on the reaction between a phenol and bromine m the titration medium III-1 contammg 60% v/v acetIc acid, 40% v/v water and being 0 1M with respect to so&urn bromide If a phenol produces titration curves hke those labelled A m Fig 1, when 20 meq are titrated m this medium under standard condltlons, It 1s considered to be activated If the consumption of bromine 1s small and a titration curve hke B m Ftg 1 IS obtained, the phenol IS said to be fully deactlvated Naturally not all phenols can be classified as either activated or fully deactivated There are mtermedate types which have a certain bromine consumption without givmg a usable titration curve (see C m Fig 1) This kmd of phenol IS considered to be partly deactivated Of the phenols titrated earlier,’ all but one turned out to be activated according to the test Only 4-hydroxyblphenyl was partly deactivated Of the phenols titrated m the present work, most were fully deactivated However, those phenols which contamed one chlorine atom and one methyl group were partly deactivated and 4-bromo-3,5dimethylphenol was activated The test falls for 2,4,6-trltert butylphenol which, although activated, gives a type B titration curve It IS evident that not only tlns phenol but all phenols m which all ortho and para positions are occupled, and whrch do not form bromocyclohexadlenones’ * For exceptions see Table 1

Quantltatwe brommatlon of deactwated phenols

As seen from Table 1, pyrlclme-contammg titration media must be used throughout for the quantitative brommatlon of deactivated phenols No quantltatlve monobrommatlon 1s possible for this type of phenol, with the standard media m Table 1 of ref 1 There 1s nonetheless m Table 1 of the present paper one phenol, 4-bromo-3,5dlmethylphenol, which can be quantitatively monobrommated, but this compound IS activated according to the test above In the following, the titration results for various types of deactivated phenols will be discussed m some detail Halophenols Most of the halophenols without alkyl groups can be titrated m medium 11-l (55% HOAc, 40% H20, 5% C,H,N and 0 IM with respect to NaBr) 3,5Dlchlorophenol, being more reactive, requires a slightly slower medium (II-2,0 4 M with respect to NaBr), presumably because the two ortho-directmg chlorme atoms are placed ortho to the free positions m the phenol The two lodophenols tested, namely 2- and Ciodophenol, were found to react slugg~hly with bromine, even m the fastest medium available (I-l), and the titration curve could not be quantitatively evaluated It was observed that the electrodes were easily contaminated m this case As expected, the presence of alkyl groups m addition to halogen atoms m the molecule generally makes It more reactive Thus, the three phenols with one chlorine atom and one methyl group were quantitatively brommated m medium II-2 while, for the correspondmg chlorophenols without alkyl groups, mechum II-1 was required 4-Bromo3,5-dimethylphenol ddTers from the other halophenols m Table 1 m that it IS an activated phenol Accordmgly It can be monobrommated m the pyndme-free medium III-2 For Its full brotnmation, medium II-2 1s necessary This fact indicates that 2,4-chbromo-3,5-dimethylphenol 1s more reactive towards bromine than the correspondmg chlorophenol, wluch had to be titrated m medium II-1 The two trifluoromethylphenols form a specutl type of halophenol as the halogen atoms are placed m the side-&am instead of m the rmg Obviously the deactivating effect of a tnfluoromethyl group IS greater than that of a fluorine atom, as a faster titration medium had to be used m the former case Carboxyphenols Of the carboxyphenols tested only mand p.hydroxybenzcuc acid can be titrated quantltatlvely

1044

SHORT CQMMUNICATIONS

Table 1 Brommatlon of deactivated phenols Phenol

Tltr medmm

We;ght*, w Ca c Found

ET -04 -03 + 14 + 14 + 04 -06 - 14 -27 + 18 +12 +03 +06 + 06 +12 +26 +34 -25 -18 +08 + 13 + 05 +01 +17 -04 +16 + 20 + 17 +17 - 13 -07 -08 -08 +08 +08

2-Fluoro

II-1

5605

3-Fluoro

II-1

3736

CFluoro

II-1

5605

2-Tnfluoromethyl

I-l

8106

3-Tnfluoromethyl

I-l

5403

2-Chloro

II-1

6798

2-Chloro-5-methyl

II-2

7085

558 559 379 379 563 557 799 789 550 547 682 684 713 717

2-Chloro-6-methyl

II-2

1417

3-Chloro

II-1

4286

4-Chloro

II-1

6428

4-Chloro-3-methyl

II-2

7085

2,4-Dlchloro

II-I

1630

2,4-Dlchloro-3,5-dlmethyl

II-1

1910

2,5-Dwhloro

II-1

8150

3,4-Dlchloro

II-1

8168

3,5-Dlchloro

II-2

6320

2,4,5-Tnchloro

II-1

1974

1454 1465 418 421 648 651 712 709 1657 1624 1940 1949 829 829 806 811 627 627 2020 2023

Phenol

Tltr medmm

Weight*, 119. Error, Calc Found %

2-Bromo

II-1

9114

4-Bromo

II-1

865 1

4-Bromo-3,5dnnethylt 2,CDlbromo

II-2

7710

II-1

2474

3-Carboxy

II-1

4604

4-Carboxy

II-1

4542

2-Formyl

I-l

6106

3-Formyl

I-l

4067

4-Formyl

II-1

6106

4-Acetyl

I-l

6810

2-Nltro

I-l

6956

3-Nltro

I-1

463 7

4-Nltro

I-l

6956

2,4-Dmltro

I-l

1841

2,6-Dmltro

I-l

1841

Phenolphthalem

II-2

7953

916 917 869 859 776 779 2452 2452 464 466 463 462 622 623 404 397 624 630 690 689 710 708 461 466 708 709 1854 1863 1835 1855 815 810

t 05 t @6 t 05 - 0.7 t06 + 10 - O-9 - 0.9 + 08 t 12 t19 t 17 t19 + 20 -07 -24 +22 t32 + 13 + 12 t21 t18 -06 +05 +18 + 19 +07 + 12 -03 + 08 +25 +18

* This weight consumes about 20 peq of bromme t Can also be quantltatlvely monobrommated m medmm III-2 with an error of about 1%

Sahcyhc acid consumes more than the expected 4 equlvalents of bromme per mole, but the result 1s not reproducible The shght overconsumptlon IS presumably caused by a partial decarboxylatlon The same reaction, although quantltatlve, takes place for p-hydroxybenzolc acid which consumes 6 equivalents of bromine instead of the expected 4 Decarboxylatlon has been reported before m connectlon with phenol brommatlon 4*5However, it should be noted that m a previous mvestlgatlon by one of the present authors,6 m whzh sahcyhc acid was titrated m acidtied acetlc acid solution with bromide-bromate m aqueous medium, no decarboxylatlon was observed, the consumption bemg 4 equivalents of bromme Delgado’ reported the quantltatlve determmatlon of sahcychc acid m aqueous medmm at pH 3 We have venfied this result, usmg his titration medium and our standard condltlons Obviously the composltmn of the tltratlon medmm 1s of declslve lmportance for the course of the brommatlon reaction. Formylphenols Of the titrated hidroxyb-enzaldehydes the orrho and meta Isomers reqmre the fastest medmm (I-l) with loo/, pyrldme whde p-hydroxybenzaldehyde gves high values m this medium and should be determined m medium II-1 The high values might arise from a partial deformylatlon 4 Acetylphenols Of the compounds tested o-hydroxyacetophenone was found not to react with bromine m any tltratlon medium used m this work This somewhat surprlsmg fact m&t be attributed to a deactlvatlon due to

the hydrogen bond between the phenohc hydroxyl group and the oxygen atom m the acetyl group smce the corresponding pnra isomer can be titrated with good accuracy It 1s noteworthy that t% medium used by Delgado” also failed for o-hydroxyacetophenone, accordmg to our expenence Nltrophenols These are strongly deactivated and accordingly for all mtrophenols the fastest medium (I-l) has to be used Phenolphthalern This phenol may be expected to be actlvated but on the basis of a type B tltratlon curve, obtamed m medmm III-l, was found to be deactivated Consequently quantitative brommatlon demands a pyndme-contaming medium (11-2) Since 8 equivalents of bromme are consumed, It appears that 2 hydrogen atoms m each of the two phenohc rings are exchanged for bromine

CONCLUSIONS

The present work has shown that the coulometrlc brommatlon method developed ongmally for the quantitative determmatlon of alkylphenols IS also applicable to the brommatlon of deactivated phenols contammg various electron-wlthdrawmg subsfituents A fast medmm, contammg pyrldme as a brommatlon promotor, has to be used throughout Although the majonty of the compounds tested could be determmed with good accuracy, d&ficulty was expen-

SHORTCOMMUNICATIONS enced with certain phenols contammg ortho substituents capable of formmg a hydrogen bond with the phenobc hydroxyl group Thus sahcyhc and and o-hydroxyacetophenone could not be titrated Although the former reacted, the results were maccurate owmg to Incomplete decarboxylatton The latter compound totally faded to react. The only two Iodophenols tested give another example of a phenohc type which could not be assayed For unknown reasons they reacted sluggishly and gave a sloping titration curve which did not perrmt any determination of the equivalence point

1045 REFERENCES

1 B Kmberger, L E Edholm, 0 NIlsson, and B Srmth, T&n& 1975, 22, 979 2 H J LIchtenstem, J Pruct Chem, 1958, 6, 225 3 0 A Delgado, Reu Fat Ing Quun Argentma, 30.85 4 A W Francis and A J Hill, J Am Chem Sot, 46.2498 5 A R Day and W T Taggart, Ind Eng Chem, 20.545 6 B Smith, Acta Chem Stand, 1956,lO. 1589

E F

1961, 1924 1928,

Summary-A number of deactivated phenols contammg fluorine, chlorine or bromme, formyl, acetyl, carboxyl or mtro groups have been titrated with anodically generated bromine The reaction was carried out In a water-ace& aad-pyrIdme medium and the reactivity was controlled by varymg the water and pyrIdme Content and the concentration of bromtde Ion Hydrogen In all free posItIons ortho and para to the phenohc hydroxyl group Is generally exchanged for bromme, but In certain mstances a partial brommatlon Is possible The method as developed Is widely applicable for deactivated phenols Only certain or&-substituted phenols could not be quantitatively titrated The mean relative error for the phenols titrated was f 1 2%

Tolantu, Vol. 22, pp 1045-1047

Pergamon

Pres$ 1975 Pnnted 10 Great Brttun

THE TITRATION ERROR IN POTENTIOMETRIC PRECIPITATION TITRATION P 0

KOSONEN and E J. HAKOILA

Department of Chermstry, UmversIty of Turku, SF-20500 Turku 50, Fmland (Recewed 26 February

1975 Accepted 8 Aprrl 1975)

The general theory of potentIometrIc precipitation tItratIon and the theoretical error In the titration have been dIscussed by many mvestigators ‘-lo When the reactIon that takes place In a preclpltatlon tItratIon Is expressed by mA + nB +A,B, (1) and the solublhty product of the sparingly soluble salt by K, = [A]“[B]

(2)

When the concentrations of IndIvIdual Ions are expressed as molarltles and the total concentrations of the solutions taking part m the reaction are expressed In normahtles the buffer capacity P at the InflectIon point of the tItratlon Is obtained by means of the equatlon4 P,,, = 2 303 x (m + n){(~~-mKs~“m+“i The error of the titration, (molar concentrations given bv6 _ -

(7) only) IS

U(m+n)

at the Inflection pomt of the titration curve the molar concentratIons of the ions are3v4

(8)

The InflectIon point of the titration curve and the eqmvalence pomt of the titration comclde when m = n M and

PRINCIPLES

[B-JM,

=

At the equivalence point of the titration the concentrations are given by’~g~4

Let us express the precipitation reactIon by equahon (1) and the solublhty product by equation (2) Let us further assume that the Indicator electrode responds to the variation of the concentration of Ion A After a permanent preclpltate has been formed we have cA =

[A].,

=

and l/on+n)

TcB-

y~,“n[A]-“n

+ [A]

(9)

where the total concentrations of A and B are denoted by CA and C, By differentiating this equation with respect to pA we get the buffer Index (BA= -dC,fdpA = 2 303 [A] dC,/d[A], for A as titrant), and by differentiating the Index with respect to pA and setting the result-