THE PREPARATION OF 9-(Z)-RETINOIC ACID

摘要

A process for preparing 9-(Z)-retinoic acid from mother liquors from the industrial preparation of C15-triarylphosphonium salts of the general formula I See Formula I where R1 to R3 are each aryl and X.THETA. is halogen or (HSO4).THETA., in an organic solvent, which comprises A. increasing the proportion of 9-(Z)-C15-triarylphosphonium salt in the C15-triarylphosphonium salts isolated from the mother liquor by treatment with isopropanol at elevated temperature, cooling and separating off the all-(E)-C15-triarylphosphonium salt which has crystallized out, B. subjecting the resulting C15-triarylphosphonium salt to a Wittig reaction with an alkyl .beta.-formylcrotonate of the general formula See Formula II and C. hydrolyzing the resulting oily retinoic ester mixture in a C3-C9-alkanol, preferably in a propanol or butanol, precipitating the resulting 9-(Z)-retinoic acid where appropriate by other adding methanol as crystals, with all-(E)-retinoic acid and retinoic acid isomers remaining in the alkanolic solution.