Maleic anhydride in the study of naturally occurring isomers of vitamin A

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Abstract
The reactions of crystalline vitamin A alcohol, acetate and palmitate with maleic anhydride in benzene solution were studied. The alcohol form reacts much more rapidly than the esters. A study of the reaction of maleic anhydride with saponified vitamin A extracts from various marine sources enables the percentages of "fast"- and "slow"-reacting isomers to be calculated. (The former comprise all-trans, 7-cis and 9-cis vitamin A, and the latter 11-cis, 13-cis, 9:13-di-cis and ll:13-di-cis vitamin A). The "slow"-reacting isomers may be isolated from the reaction mixture by adding ethanolic potassium hydroxide, then water, and extracting with light petroleum. An example is given of the preparation of 13-cis vitamin A alcohol from a commercial vitamin A preparation.