Stability of Retinol Analogs. VIII. Pyrolysis and Photolysis of Retinoic Acid in Aqueous Ethanolic Solution

Abstract

In order to study the decomposition of retionic acid in aqueous solution without surface-active agent, retinoic acid was dissolved in aqueous ethanolic solutions which contained various amount of water, and its thermal decomposition and photodecomposition was investigated. (1) In pyrolysis, retinoic acid was more stable than retinol or retinal. When water content was increased, the stability of retionic acid did not change as that of retinol and retinal. In photolysis, retinoic acid was decomposed rapidly, and its stability was not largely affected by N2 gas exchange and increasing water content. (2) Two decomposition products were recongnized, as the common decomposition products of retionic acid in pyrolysis and photolysis. The one seemed to be decarboxylated retinoic acid and the other seemed to be formed by the addition of a decomposition product to retinoic acid. In photolysis, additionally three other substances were recognized, the one was ethyl retionate and the two other substances seemed to be isomers of retinoic acid. (3) In photolysis, all-trans-retinoic acid was isomerized into 13-cis- and 9,13-di-cis-isomers, but isomerization did not occur in pyrolysis. © 1979, The Pharmaceutical Society of Japan. All rights reserved.