II. CHEMISTRY 531 



anol-(peroxide free) other mixture, again with a melting point of IGG to 

 167°. 



B. CHEMICAL AND PHYSICAL PROPERTIES 



The biotin methyl ester is sohible in methanol, ethanol, acetone, and 

 chloroform, sparingly soluble in ethyl acetate, and almost insoluble in 

 water and ether. It is optically active; [a\^ = +57° for a 1 % solution in 

 chloroform. 



The correct empirical formula, CnHisOsNaS, for biotin methyl ester 



Fig. 1. Biotin (free acid) crj^stallized from water (magnification 100 X). From 

 D. B. Melville. Vitamins and Hormones 2, 40 (1944). 



was reported in 1937 by Kogl,-* and confirmed by du Vigneaud et al.^^ 

 Spectroscopic studies revealed no specific bands for biotin methyl ester 

 in the range from 2200 to 0000 A.^^- 27 



The biotin methyl aster is readily saponified with dilute alkali at room 

 temperature. After acidification with dilute hydrochloric acid and con- 

 centration free biotin is obtained in crystalline form from the saponification 

 mixture.-^ After recrystallization from water the long fine needles (Fig. 1) 

 of free biotin melt with some decomposition at 230 to 232° (uncorrected). 

 Free biotin is soluble in dilute alkali and hot water, sparingly soluble in 

 dilute acid and cold water, and practically insoluble in organic solvents. 



" F. Kogl, Naturwissenschaftcn 25, 465 (19.37). 



" V. du Vigneaud, K. Hofmann, D. B. Melville, and J. H. Kachele, J. Biol. Chem. 

 140, 763 (1941). 



