Titrimetry in Glacial Acetic Acid Determ'ination of Choline Salts of Carboxylic Acids PETER C. MARKUNAS AND JOHN A . RIDDICK Research and Development Department, Commercial Solcents Corp., Terre Haute, Ind. The purpose of this study- was to develop a rapid and accurate method for the determination of choline salts of carboxylic acids. The choline salt is dissolved in glacial acetic acid and titrated with perchloric acid in acetic acid. By a slight modification, the method was also adapted to the aqueoussolutions of these choline salts. The method is as precise and
accurate as aqueons acidimetric procedures and w-hen applied to the analysis of production samples seems to have no error in excess of fO.2c/c. Both dry and aqueous solutions and purified and technical choline carboxj-licacid salts may be analyzed. The method has proved a most conrenient and rapid means of process control and analysis.
T
form beaker, without spout, dissolved in 30 ml. of glacial acetic acid, a-armed if necessary to effect solution, cooled to room temperature, and titrated potentionietricaally with 0.1 S perchloric acid in acetic acid. The titration is conducted and the equivalence point determined in the manner employed for a potentiometric titration in aqueous solution. Indicator Titration, Method 11. The same Ii-eight of sample as required for the potentiometric method is accurately weighed into a 250-ml. Erlenmeyer flask and dissolved in 30 ml. of acetic acid. One drop of crystal violet indicator is added and the solution is titrated to a blue-green color with the 0.1 -1-perchloric acid solution.
WO accurate gravimetric methods for the determination of
choline salts have recently been proposed. One is h e e d upon the formation of an ethanol-insoluble complex compound of choline chloride and cadmium chloride, (CH,)3SCI.C2H,0H.CdCll (6). The other is based upon the prrcipitation of choline as the'reineckate ( 4 ) . The latter has an advantage over the former in that the choline may he precipitated from an aqueous solution. However, both methods have the disadvantage inherent in gravimetric procedurcs-they are t imc-consuming in comparison t o volumetric procedures. I n a preliminary survey of the usefulness of a proposed technique employing titrimetry in glacial acetic acid for the analysis of carboxylic acid salts and weak bases, it was shown that choline dihydrogen citrate can be determined by titration with perchloric acid in glacial acetic acid (3). The survey, however, was limited to the testing of compounds of highest purity commercially available and no effort was made t o apply the method t o the determination of any particular compound nor t o demonstrate its usefulness in production control or in the anal? mixtures. This titrimetric method has now been applied t o the deterniination of choline gluconate, choline dihydrogen citrate, and choline hydrogen tartrate in purified and technical grade preparations and to aqueous solutions of these choline salts. From data obtained during the preliminary survey, it is concluded that the method is applicable also t o t,he determination of other carboxylic acid salts of choline, but not t o choline chloride. This latter compound, however, can be determined by the recently proposed procedure sf Pifer and Wollish ( b ) .
EXPERIRIENTA L
Precision and Accuracy. A sample of recrystallized choline dihydrogen citrate analyzed by the procedure outlined i n llethod I1 gave the following values: 99.92, 99.87, 100.04, 99.99, 100.05, and 100.05; average 9Q.9SVc. The same sample analyzed by the potentiometric procedure, Method I, gave values of 100.03,100.05, 99.91, 99.94, and 99.95; an average of 99.98%. The mean deviation for the replicate values for choline dihydrogen citrate by Method 1 is i O . O 5 % and by Method I1 is j=O.O6CI,.
Table I. Sample Solution 1
2 3
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REAGENTS AND APPARATUS
6
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The reagents and apparatus used were those outlined in the original paper (5),except for the choline salts. Choline dihydrogen citrate was purified by recrystallization from a mixture containing equal volumes of ethanol and methanol and dried in a vacuum oven a t room temperature. Choline gluconate solution was prepared by adding about 5% excess of gluconic acid to an aqueous solution of choline base and removing part of the water a t reduced pressure. Choline bicarbonate solution was prepared by passing carbon dioxide int,o an aqueous solution of the free choline base. Choline hydrogen tartrate was prepared by adding a 2% excess of tartaric acid to a solution of choline bicarbonate and removing all the water under vacuum. The choline dihydrogen citrate, gluconate, and bicarbonate were found to contain less than 0.05% trimethylamine. Sample Solution of Choline Dihydrogen Citrate. About 46 grams of choline dihydrogen citrate, accurately weighed, were dissolved in glacial acetic and transferred quantitatively t o a 1liter volumetric flask. The solution was allowed to reach room temperature, and made t o volume.
Effect of Water on Assay of Choline Dihydrogen Citrate Water Added
.4pproximate Water Content of Samplea
.M1.
%
0.0 0.1 0.2 0.4 0.8 1.6 2.0
0 10
15 26 41
58 63
Choline Dihydrogen Citrate Found
% 99.98, 100.00 99.95, 99.95 9 9 . 9 5 , 99.98 100.03,100.00 100.46, 100.46 101.85,101.85 102.66. 102.69
a Calculated from weight of sample introduced (in 2 5 ml. of sample solution) and water added.
Interferences. Ethyl acetate, ethyl ether, acetonitrile, acetone, p-dioxane, nitronirthane, benzene, petroleum ether, and carbon tetrachloride do not interfere with the titration of choline salts of carboxylic acids when any of these compounds comprise as much as 10% by volume of the original solvent. The effect of larger amounts of these solvents was not determined. However, no interference is expected, as it was recently shown that many of these reagents can be used in nonaqueous titrimetry (2). The presence of either ethanol or methanol in the solvent or sample appears t o decrease slightly the basicity of choline salts in glacial acetic acid but otherwise does not interfere with the assay. Trimethylammonium carboxylic acid salts, if present in the choline preparation, will be titrated and determined a8 the choline salt. This is not a serious interference because it is possi-
PROCEDURE
Potentiometric Titration, Method I. A sample containing about 3.5 milliequivalents of salt is accurately weighed into a tall-
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V O L U M E 2 4 , N O . 2, F E B R U A R Y 1 9 5 2 Table 11.
Solution
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Determination of Choline Dihydrogen Citrate i n Presence of Water IVata. Added
Ipuroxiinate Water Content of Sample
Jri.
R
Choline Dihydrogrn Citrate Found, Indicator Potentiometric End Point End,Point ~
and free tartaric acid content of l.95yo was assayed by Method I . An average value of 96.91Y0 was obtained. A production sample of choline gluconate, manufactured t o contain very close to 62.5% choline gluconate, assayed by Method 111 (indicator end point) gave replicate values of 62.15, 62.14, 62.09, 62.12, 62.04, 62.00, 62.09, 62.11, and62.07; average 62.09%. This sample had free gluconic acid and moisture contents of 5.1 and 32.9y0, respectively. These trvo examples illustrate the applii~aliilitj- of the described methods t o the analysis of production sample? of choline carboxylic acid salts and demonstrate t h a t the proposed procedures seem t o have no error in excess of &0.2%. DISCUSSION
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ble t o correct for presence of t h e trimethylammonium salt after determining its content b y a recently developed method (1). Small amounts of water have no detectable effect upon the determination of choline carboxylic acid salts, b u t large amounts of Ivater give high results. The magnitude of thi? c,ffcc:t is indicated by the values in Table I. Determination of Choline Salts in Presence of Water. By a slight modification of the described procedure it is possible to assay accurately samples of choline salts containing as much as YOc; Tvater. This modification, designated Method 111, consists of adding sufficient acetic anhydride t o the sample in acetic acitl to react with the water introduced with the sample, very gently boiling the mixture for 5 minutes, cooling to room temperature, and titrating with the 0.1 S perchloric acid solution, using either the indicator or potentionietric procedure to obtain the end poitit. \Vhen Method I11 was applied t o a number of 25-1111. aliquots of the sample solution t o n-hich known amounts of water ~\-rrcfi :ttlded, the values shonn i n Table I1 were obtained. - i n approximately SOYo aqueous solution of choline ljicarboiiate aiialyzed 1)y a n aqueous aridiniet ric. procedure gave v d u e s of 49.49, 4‘3.4‘3. 49.46. 19.43, 49.40, ant1 19.14; a \Then this sample was analyzed ljy llethod 111, employing an indicator end point, the results olitaineii were: 19.38, 19.38, 49.44, 49.45, 49.42, and 49.43: average 40.42%. These values not only indicate the high precision and aveuracy of Mrthod I11 but also substantiate thtl fact t h a t the dlrsrrihed nonaqueous titrimetric procedure is as precise a n d :tccuratr a s acjucous acidimct t,ic, ani1 alk:~linit~t ricu n w t h o d ~ . Application. A siiiipl[> of c.holinr hydrogtiii tartrate ivliich had a nioisturc content of l.OOyo (b>-the liar1 Fischer niethod)
When aqueous solutions of choline dihydrogen citrate or choline hydrogen tartrate are analyzed by Method 111, slightly lower results are obtained by t h e indicator t h a n hy the potcntiometric end-point procedure. This is due t o the slight obscuring of the indicator end point by darkening (browning) of the soliition during t h e refluxing period. The discoloration dors not interferr ivith tlie a w i j - , and after a few trials the end point c a n be duplicatctl without difficulty. The discoloration i1ow not occur \\.it11 clioliiic~yluc.ontite or bicarbomtr. The :iiiiount of a c h e anliydride added in 3Iethod I11 is not critical. E s i w s acetic anhydride does not interfere n-ith tlicx determinatioii :tiid equally good results can be obtained if only enough snliydritlc. is wdded t o rlract Il-ith 80 t o (90y0of t h e n-atvr iiitrotluwcl \\-ith t hc, r;rmple. ACKNOWLEDGMENT
The authors ivieh t o express their appreciation t o Joseph B. Creedon for pi~rforniingmany of the titrations during the course of this work. LITERATURE CITED
(1) Cundiff, R . X., arid Riddick, J. .4., - 1 s . 4 ~ . CHEM.,in press. ( 2 ) Fritz, 3.S.,I b i d . , 22, 1028 (1950). (3) Rfarkunns, P. C., and Riddick, J . A , I h i d . , 23, 337 (1951). (4) Pankratz, R. E., and Bandelin, F. J., J . d m . Pliarm. -4s,poe., Sei. Ed., 39, 238 (1950).
(5) Pifer, C. IT.,and Wollish, E. G., ANAL.CHEM.,23,300 (1961). (6) Seaman, IT.,Hugonet, J. J., and Leibmann, W., I b i d . , 21, 411
(1949). RECEIVED January 26, 1931. Presented as part of discussion on titrations in anhydrous solvents before the Fourth Symposium on Bnalytical Chemistry, Indiana Section, . h E R I C A S C H E m C A L SOCIETY, S o r e i n b e r 4, 1Y60.
Fatty Amine Products of High Molecular Weight Quantitative Titration in Acetic -4cid DAVID E. TERRY, KEKDRICK R. EILAR, AND OWEN A. MOE Chemical Laboratories, General Mills, Inc., Minneapolis, Minn.
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QCEOCS titrimetry appears adequate for the fatty primary amines of high molecular weight. However, i t has been found of little or no value when applied t o t h e acetates of the f a t t y primary amines, which are commercial products useful in ore beneficiation, and certain secondary and tertiary amines of high molecular weight. This paper concerns the adaptability of titrimetry in glacial acetic acid t o diverse fatty amine products of high molecular weight. Conant and Hall ( 3 ) in their study of “superacid solutions” found t h a t many organic compounds behave as strong bases in glacial acetic acid whereas they show no basic property in water. I n view of the acid-base relationships which exist in glacial acetic acid (1, 3-6, 7, 8, 1 1 ) , it appeared probable t h a t these fatty
amine products could be quantitatively titrated in glacial acetic acid with perchlolic acid. Bccordingly, different compounds such as the fatty primary amine acetates, fatty secondary amines, mixed tertiary amines, f a t t y aniinonitriles-for example, ,Y-alkylp-aminoproptonitriles-and fatty materials containing both primary and secondary amino groups-for example, -Y-alkyl-yaminopropylamines-were tested. I n the present study, i t was found t h a t glacial acetic acid was a n excellent solvent for all the fatty amine products tested and perchloric acid was a highly satisfactory titrant. REAGENTS AND SOLUTIONS
Perchloric acid, 70 to 72%, ACS grade Acetic anhydride, ACS grade
