702 VII. VITAMINS A 



petroleum ether with dikite aqueous potassium permanganate containing 

 sulfuric acid. On chromatographic separation, small amounts of material 

 were always present with an absorption maximum at 365-370 m^ in satu- 

 rated hydrocarbon solvents, and 385 m/x in chloroform. These workers 

 found that the material obtained by chromatographic separation also 

 reacted with antimony trichloride; the maximum band appeared at 665 

 m^. Presumably the compound at hand was vitamin Ai aldehyde. 



Hawkins and Hunter,^" likewise, synthesized vitamin Ai aldehyde from 

 vitamin Ai by the Oppenauer reaction; however, the preparation was ap- 

 parently impure, as it showed an absorption maximum not only at 368 mju 

 but also at 350 m^. The authors reported a maximum absorption at 657 

 m/x when it was reacted with antimony trichloride. However, when the 

 preparation w^as examined by Ball, Goodwin, and Morton,^ ^ it was found 

 that the variation from the earlier color maximum of 664 m^ Avas a result of 

 spectroscopic technic only. Hunter and Williams '"^^ obtained the aldehyde 

 by the oxidation of jS-carotene. This is of great interest, as it provides 

 chemical proof of the conversion of the provitamin A, jS-carotene, to 

 vitamin A. 



Van Dorp and Arens^*'^ synthesized the vitamin Ai aldehyde in the course 

 of a synthesis of vitamin A alcohol (see Section 5). The most satisfactory 

 procedure for the preparation of vitamin Ai aldehyde has been recently 

 reported by Ball, Goodwin, and Morton.^^ Vitamin Ai was oxidized in 

 light petroleum with manganese dioxide for 6 to 10 days in the dark; yields 

 of the aldehyde as high as 80% of the theoretical were obtained. The vita- 

 min Ai aldehyde was separated chromatographically on an alumina 

 (Brockmann) column; the slow-travelling brown zone proved to be the 

 vitamin Ai aldehyde. After removal of some impurities which crystallized 

 from petroleum ether at -72°C., the mother liquor was concentrated 

 to one-fourth volume. A brown semisolid mass separated after 24 hours 

 at — 72°C. After recrystallization of this mass from petroleum ether at 

 — 72°C. for 10 days, reddish brown crystals were obtained, which melted at 

 56.5 to 58° C, and which showed a single maximum in cyclohexane at 373 

 mn. After a final recrystallization from petroleum ether, orange-red crystals 

 were obtained; these were large clusters, predominantly needle-like, which 

 melted at 61-62°C. 



Ball et al.^^ note the following values for maximum aljsorption of vitamin 

 A aldehyde: light petroleum ether (40-60°), 369.5 m/x; cyclohexane, 373 

 m/x; ethanol, 385.5 m/x; chloroform, 389 m/x. The extinction values, 

 £" (1%, 1 cm.), in these various solvents at the maximum absorption are as 

 follows: light petroleum ether (40-60°), 1685; cyclohexane, 1548; etha- 

 nes R. F. Hunter and N. E. Williams, J. Chem. Soc, 1945, 554-556. 

 163 D. A. van Dorp and J. F. Arens, Nature, 160, 189 (1947). 



