Crystalline esters of vitamin A

Abstract

I. By distillation in the Hickman cyclic still vit. A has been obtained in a high state of purity and crystallized directly from methyl alcohol at a low temperature. The stearate, 4-nitrobenzoate, diphenylacetate and acetate have been prepared but not in crystalline form. Crystalline anthraquinone-2-carboxylate and 2-naphthoate, also prepared from a molecular distillate, resembled the anthraquinone-2-carboxylate and 2-naphthoate prepared by Hamano from undistilled concentrates. II. By biological tests, in terms of the international standard [beta]-carotene, vit. A anthraquinone-2-carboxylate contained 1,750,000 units per g. and vit. A 2-naphthoate 2,225,000. The potency of vit. A ale. is therefore 3,181,000 or 3,424,000 i.u. per g. according to the 2 tests. Since, by definition, [beta]/3-carotene contains 1,670,000 i.u. of vit. A activity per g. vit. A itself is twice as active as [beta]carotene, wt. for wt. The factor for converting the coefficient of absorption at 328 mu into biological units per g. (conversion factor) was found to be about 2000.