Color reaction of cholesterol in concentrated trichloroacetic acid media.

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Abstract
Reaction product of the coloration of cholesterol in 90% liquefied trichloroacetic acid (conc. TCA) and its mixture with hydrochloric acid were investigated in order to find the relationship between the coloration and the reaction products. It was found that 3, 5-cholestadiene was the main product in all of TCA-containing media and 3, 3'-bis (3, 5-cholestadiene) was the minor product in conc. TCA-HCl (10 : 1) medium, while any of bissteroid was not found in the reaction with conc. TCA-HCl (1 : 1) medium. The colored solution of these compounds showed the similar absorption spectrum to that of cholesterol in the respective medium. Cholesteryl chloride, which developed a red color gradually on dissolving in conc. TCA-HCl (10 : 1) and (1 : 1) media, was also obtained from the colored solution of cholesterol in all of HCl-containing media, and 3, 5-cholestadiene was isolated from the colored solution of cholesteryl chloride. These results suggested that cholesteryl chloride might not be a direct coloring substance but 3, 5-cholestadiene or a coloring intermediate derived from cholesteryl chloride in these media might contribute to the coloration.

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