J. V. Krishna eddy ond K. s. Boparai Vikrom University Uijoin, 456 010 India
Benzylthiuronium Bicarbonate for the Derivatization of Carboxylic Acids
Various isothiuronium halides (1-6) have been suggested for the characterization of carboxylic acids. The procedure involves the preparation of a neutral solution of the sodium salt of an acid. The p H of the solution has to be adjusted carefully, because the derivatization is difficult if the DH is below 7: and if the DH is more than 7. the isothioureas are liberated which'decompose extensively and thus contaminate the derivative. Though the procedure is valuable, a lot of difficulty is experienced, particularly by beainners. in carwing out the derivatization. Benzylthiu&um bicarbonate has, therefore, been prepared and its use for the characterization of carboxylic acids studied. The reagent is added to the solution or suspension of the acid in water or aqueous ethanol till the effervescence almost ceases. The derivative thus obtained is used for the characterization. The procedure does not require the adiustment of pH and is particularly valuable for acids of iow molecul& weight because it is-possible to add the required quantity of the solid reagent till the effervescence almost ceases, and hence better yields are obtained. The use of the present reagent is therefore advantageous as compared to other such reagents mentioned in the literature. Experimental Preparation of Benzylthiuronium Bicarbonate Sodium bicarbonate (6.0 g), dissolved in 50 ml of water, is added dropwise with continuous stirring to a solution af benzylthiuronium chloride (14.4 g) in 50 ml of water. The precipitate thus obtained is collected by filtration under suction and washed
324 / Jownal of Chemical Education
twice with 10 ml of water. Colorless powder decomposes at 78-8O0C, yield, 15 g. Analysis: Found: C, 46.86%; H, 5.51%; N, 12.38%; S, 13.21%; CgH12N103S requires: C, 47.37%; H, 5.29%; N, 12.28%; S, 14.05%. Preparation of BenzyRhiuronium Carboxylates A carboxylic acid (0.25 g) is dissolved or suspended in 2 ml of water (for lower aliphatic acids) or 50% aqueous ethanol (for higher aliphatic acids and aromatic acids). The reagent is added intermittently till the effervescence almost ceases. The solution is chilled and the derivative is collected by filtration under suction. In the case of aromatic acids and higher aliphatic acids, the derivative often starts precipitating during the addition of the reagent. The precipitate is dissolved by warming, the solution is allowed to cool, and the derivative is collected. In many cases the derivatives were found to be pure and in the case of others crystallization from ethanol afforded pure products. The melting points of the derivatives, determined by the capillary tube method, agree well with the reported values. Acknowledgment The authors are grateful to Professor M. M. Bokadia for providing the necessary research facilities and to C.S.I.R. (India) for the award of a research fellowship (to J. V. Krishna Reddy). Literature CHed (1) O o n l s a ~J.J., , J. A m e r C h e m Soe.. 58,1001(1938). (2) Veibel, S.. sndLillelund,H.. BUl Sor. Chim.. 5151. 1153(19381. 13) Veibd, S., andottung, K.. Bull. Soc Chim., 516). 14%(19391. (4) 0eruoy.B. T.. andSpew,R. B.. J. Arne,. Chem Soc, 61,3251 (19391. 151 Dewey, B. T., sndSha.ky, H.G.,J.A~DI Chrm. Soe., 63,352611941). (61 Bauner, W.A..JAmer. Cham. Soc., 70,35QSl19481.
