Color reaction of cholesterol with trichloroacetic acid and antimony trichloride. on the reaction mechanism

Abstract

The color reaction of cholesterol with trichloroacetic acid and antimony trichloride was examined to elucidate its reaction mechanism. 3, 5-Cholestadiene, 3, 3'-bis(3, 5-cholestadiene), 3, 3'-bis(2, 4-cholestadiene), and cholesteryl trichloroacetate were isolated as the reaction products from the colored reaction mixture of cholesterol, and the first three compounds were found to be responsible for the coloration. It was assumed that cholesterol was dehydrated to 3, 5-cholestadiene and 2, 4-cholestadiene, which were dimerized to 3, 3'-bis(3, 5-cholestadiene) and 3, 3'-bis(2, 4-cholestadiene), respectively, and 3, 3'-bis(2, 4-cholestadiene) was in part converted to 3, 3'-bis(3, 5-cholestadiene) in trichloroacetic acid and antimony trichloride. The free radicals were detected in the colored solutions of cholesterol, 3, 5-cholestadiene, 3, 3'-bis(3, 5-cholestadiene), and 3, 3'-bis(2, 4-cholestadiene), and inferred to be the radical cations of the steroids. The radical cation was postulated to be responsible with respect to the mechanism of the coloration. The relationship between the color reagent and the formation of dimeric steroids was described.