uick and Simple Conversion of Carboxylic Acids into Their nilides of Heating with Phenyl lsothiocyanate Ram N. Ram, Pradeep Kumar, and Arya K. Mukerjee Banaras Hindu University, Varanasi-221005 (India) Derivatization continues to be a reaular uractice in functional group analysis of organic compounds-in student laboratories. The conversion of carboxylic acids into their anilides usually involves preparation of acid chloride or mixed anhydride followed by treatment with aniline. Also, direct condensation of carboxylic acids with aniline at elevated temperatures is known ( I ) . These methods are rather tedious andlor time-consuming. In this article we report a quick and easier procedure, using phenyl isothiocyanate ( 2 ) ,for thls purpose, which 1s ideally suited to students. Phenyl isothiocyanate and the carboxylic acid are taken in equimolar proportion, heated in a test tube at 160-170° for 10-15 min, and mixed thoroughly with a glass rod. The vlscous mass obtained was triturated with benzene or aoueous ethafiltered, and recrystallized from benzene'or aqueous ethanol. I t is noteworthy that use of pyridine as a catalyst considerably improves the yield and acetic, butyric, and o nitrobenzoic acids fail to react satisfactorily in the absence of pyridine. The course of the reaction is given in the figure and the results are summarized in the table. It can be seen that the present method is applicable even
to hydroxy, phenolic, and malonic acids, and it is more advantageous than the conventional methods. R-COOH
6
Ht
+
R--COO-
PhN=C-S
C-
o=c-0 l I R r?"
Literature Cited (1) v 0 g 4 . A . I.,~'ATe~tbookofPracticaiOrg~nicChemistry~3rded..EnglishLsngusge Book Society and Longmans, Green and Co. Ltd.,Londnn, 1988, p 361. (21 T ~ O U Ethe ~ o~phenyiisothiocyanate ~ i t carbo.y~icacids h isknown itsscope hm ,at been t h ~ ~ o u g hstudied. ~y ~ a f s iS. . i ~ d i t o i ) he , chemistry of cyanatas and Their Thio Derivatives? John Wiley& Sans, New York, 1977, Part 2, p. 1122. pp. 365.366. (,, (4) hference (11, PP. 7 7 ~ 7 7 9 . ( 5 ) Ludwig. A.,and Georiescu.RI.,Bull. Chim. Soc. Romone Chim.. 39.41 (1937-38); Chom. Ab8Lr.. 34,6067 (19401. (6) ~ i ~ h ~ s n d~ ~ a~ r k. e ~r , ~. .~~. . .h d i ~cham. " so
