Abstract
In the colorimetric reaction of vitamin D with antimony trichloride reagent containing acetyl chloride, chemical isomerization of vitamin D by acetyl chloride and a role of acetyl chloride were studied. Vitamin D_2 in ethylene dichloride was able to be easily isomerized to isotachysterol by acetyl chloride at room temperature. When antimory trichloride reagent without acetyl chloride was added to isotachysterol, no color was produced. Therefore, it may be concluded that the isomerization of vitamin D_2 by acetyl chloride has no relation with this colorimetric reaction.
