Abstract
Chemical isomerization of vitamin D_2 by iodine under the influence of daylight (reported by Havinga, et al.) was investigated by using the previously reported alumina-column chromatographic and gas chromatographic procedures. Small quantities of iodine was added to 2.5×10^<-3> M vitamin D_2・n-hexane solution and then the mixture was allowed to stand in daylight. When the concentration of iodine was 8×10^<-6> M, vitamin D_2 was isomerized to 5,6-trans-vitamin D_2. When the concentration of iodine was more than 8×10^<-5> M, however, it was isomerized to isotachysterol_2 through the following course : vitamin D_2→5,6-trans-vitamin D_2→isocalciferol→isotachysterol_2.
