the derivatives may be prepared without danger of precipitating the hydroxide. Also, if a minimum of alcohol is used in reprecipitating, any hydroxide that is coprecipitated will not redissolve in the first recrystallization of the derivative. Tetraphenylstibonium sulfate overcomes many of the difficulties now encountered with the qualitative analysis of organic acids. It is particularly good for the low molecular weight, watersoluble fatty acids. The salts of the acid and tetraphenylstibonium ion pre-
cipitate from dilute solutions with a minimum of preliminary preparations, and because the compound formed is a salt, the danger of oils forming is small. The salt derivatives are stable, insoluble in water, and easy to recrystallize. I n most cases the melting or decomposition points obtained are sufficiently sharp and far enough apart for the differentiation of many organic acids. LITERATURE CITED
(1) Chatt, J., Mann, F. G., J. Chem. SOC. 1192, 1940.
(2) Perkins, L. R., Ph.D. thesis, University of Michigan, 1947. ( 3 ) Potratz. H. A,. ANAL. CHEM. 28. ' 1356 (1956). ( 4 ) Willard, H. H., Perkins, L. R., Ibid., 25. 1634 (1953). ( 5 ) 6-illar& H. H., Perkins, L. R., Blicke, F. F., J. Am. Chem. Sac. 70, 737 (1948).
RECEIVED for review February 8, 1960. Accepted May 31, 1900. Presented in part at the Southwest Regional Meeting of the American Chemical Society, Baton Rouge, La., October 1959. Work supported by the National Science Foundation.
Titrimetric Determination of Carboxylic Acid Chlori de L. J. LOHR Eastern laboratory, Explosives Deparfment, E. 1. du Pont de Nernours & Co.,lnc., Gibbstown, N. 1.
)Aromatic and aliphatic carboxylic acid chlorides dissolved in tetrahydrofuran are titrated directly with cyclohexylamine dissolved in tetrahydrofuran. The end point of the titration is determined by a sudden change in potential measured with glass-calomel electrodes. Carboxylic acids d o not interfere with the titration, and the carboxylic acid in the acid chloride does not have to b e determined. Free hydrochloric acid also titrates, and the acid chloride titration must b e corrected for the free hydrochloric acid present.
P
and ammonia have been utilized indirectly in various methods of determining carboxylic acid chlorides. In the method of Pesez and Willemart (3), one sample of the acid chloride is reacted with aniline in dioxane t o form an anilide and aniline hydrochloride, and another sample is hydrolyzed with water. The acid chloride is calculated from the difference between the base consumed in the titration of the hydrolyzed sample and in the titration of the sample reacted with aniline. I n the method of Bauer (a), the fatty acid chloride in mixtures of the acid chloride and the fatty acid is converted to the neutral anilide. After acidification with hydrochloric acid, the excess free hydrochloric acid and the aniline hydrochloride are washed from the anilide and the fatty acid is titrated. The per cent fatty acid chloride is calculated by difference. Ackley and Tesoro ( 1 ) similarly analyzed mixtures of fatty acid chlorides and fatty acids by converting the acid RIMARY AMINES
1 166
ANALYTICAL CHEMISTRY
chloride to the acid amide with ammonia. In the more direct method of Stahl and Siggia (6),the carboxylic acid and acid chloride are determined after reaction of the sample with m-chloroaniline. A resulting aqueous solution of m-chloroaniline hydrochloride and the carboxylic acid is titrated differentially with aqueous base. Free hydrochloric acid, if present, must be determined by a nonaqueous titration of a separate sample ( 4 , 6 ) . These methods are unsuitable for determining carboxylic acid chlorides which have an easily hydrolyzed group such as -CH2C1, -CHC12, or -Cch, or for determining carboxylic acid chlorides in mixtures which contain other compounds having these unstable groups. This paper describes a direct nonaqueous titration of simple and complex aliphatic and aromatic carboxylic acid chlorides. The method was developed mainly for determining aromatic acid chlorides having an easily hydrolyzed group such as -CH,Cl, -CHC12, or -CC13, and for determining aromatic difunctional carboxylic acid chlorides, such as terephthaloyl and isophthaloyl chlorides, Khich may contain impurities having these groups. The method is general and can be used to determine other simple carboxylic acid chlorides such as lauroyl chloride. The determination of aromatic difunctional acid chlorides such as terephthaloyl chloride, or of aromatic acid chlorides having a group which is easily hydrolyzed in basic solution, such as -CH2C1, -CHCL, or -Cch, has not been discussed in the literature. The acid chloride dissolved in tetrahydrofuran is titrated r i t h a standard
solution of cyclohexylamine also dissolved in tetrahydrofuran. The end point is determined by a sudden potential drop measured with glasscalomel electrodes. Carboxylic acids do not titrate, and consequently do not interfere with the titration of the acid chloride. The acid chloride titration must be corrected for any free hydrochloric acid in the sample. Free hydrochloric acid is accurately determined by titration of a separate sample with tripropylaniine (4, 5 ) . DETAILS OF METHOD
This titrimetric method is based upon the general Reaction A. "",-"GI
U where R = aliphatic or aromatic. As the titration proceeds, most of the products of the reaction separate from the solution. The stoichiometry was proved by Reaction B.
181
6)6-0e-rg 6"'' +
+
1
L
COC,
O H T.rephfhololl C h orld,
C,:I~h.Womine
U
N,N'-D
