Photochemical isomerization of vitamin A compounds

A process for the photochemical isomerization of a compound of the formula:

• ##STR2## wherein X is selected from the group consisting of --CHO, --CH.sub.2 OH, --COOH, CH(R).sub.2, --CH.sub.2 OR.sub.1, --COOR.sub.2, --CONHR.sub.3 or --CON(R.sub.3).sub.2 in which R is lower alkoxy or two R's taken together are lower alkylenedioxy, R.sub.1 is alkanoyl or aroyl, R.sub.2 is an alkyl, aryl or aralkyl group and R.sub.3 is hydrogen, alkyl, aryl or aralkyl;
• which process comprises irradiating a 9-cis isomer, an 11-cis isomer, a 9,11-di-cis isomer or mixtures thereof in either liquid form or in the form of at least 3% (wt./vol.) solutions with light having a wavelength range of about 240 nm to about 450 nm in the absence of sensitizers.