Titration of sterol double bonds with dibromopyridine sulfate

Cis and trans-22-dehydrocholesteryl acetates and cis and trans-22-cholesten-3beta-yl acetates were prepared and compared to delta22-phytosterylacetates by titration with dibromopyridine sulfate. The cholesterol derivatives absorbed close to the theoretical quantity of bromine (1 Br2 per double bond), whereas the delta22-C24-alkylated sterols consumed 0.14 to 0.23 Br2 in excess of the calculated values. This excess is attributed to the formation of additional unsaturation during bromination. delta7 and delta8(14)-sterols consume more than 2 and 3 moles Br2, respectively, which indicates that at least one or two new double bonds are formed in these molecules during the bromination step.