SELECTED CIS TRANS ISOMERS OF CAROTENOIDS FORMED BY BULK ELECTROLYSISAND IRON(III) CHLORIDE OXIDATION/

Bulk electrolysis and chemical oxidation with FeCl3 of all-trans canth axanthin (I) and 8'-apo-beta-caroten-8'-al (II) gave primarily the 9- and 13-cis-isomers, which were separated by HPLC and identified by H-1 NMR spectroscopy. Optical absorption measurements showed that the 15- cis; 9,13-di-cis isomers of I are also formed by these methods. In the case of the unsymmetrical compound II, additional isomers were formed . The cis isomers account for about 40-60% of products formed. Formati on of the isomers is believed to occur by rotation about certain bonds in the cation radicals or dications, which are formed in the oxidatio n processes. The neutral cis species are then formed by an electron ex change reaction of the cis-cation radicals with neutral all-trans caro tenoids in solution. The electrochemical and iron(III) chloride oxidat ion induced isomerization are shown to be efficient and improved metho ds for forming selected carotenoid isomers.