Oxidation and isomerization of retinoic acid by iodine and light: a novel preparation of all-trans- and 13-cis-4-oxoretinoic acid

A mixture of all‐trans‐retinoic acid and iodine in heptane was irradiated. Two oxidation products were isolated by high performance liquid chromatography and identified as all‐trans‐ and 13‐cis‐4‐oxoretinoic acid by nuclear magnetic reasonance, ultra violet, Infrared spectroscopy, and mass spectral analysis. Under the same conditions, but without light, a mixture of all‐trans‐ and 13‐cis‐retinoic acid resulted. The corresponding methyl esters were obtained when methyl all‐trans‐retinoate was used in place of all‐trans‐retinoic acid.