THE VISUAL PIGMENTS 



by converting vitamin A^ to retinenci. This involved oxidation of 

 the alcohol group to aldehyde without affecting the vulnerable 

 double bonds in the molecule, morton and Goodwin (1944), by 

 shaking vitamin A concentrates, dissolved in light petroleum, with 

 dilute aqueous KMn04 in the presence of a little H2SO4 — and 

 subsequent chromatographic separation, obtained some fractions 

 which showed an absorption band at 385 vcifi in chloroform and a 

 664 m/i band on adding the antimony chloride reagent. But the 

 yields were small and not very reproducible. Morton's original 

 suggestion was also confirmed by hawkins and hunter (1944) who 

 obtained a similar material from vitamin A by the Oppenauer 

 reaction and from it prepared a 2,4 dinitrophenylhydrazone (m.p. 

 207-209°). 



Some years before wald had discovered retinene, morton, in 

 collaboration with drummond, had studied the changes in vitamin 

 A concentrates which had been left to stand over various soHds. At 

 the time, the work was unproductive but examination of the old 

 notebooks showed that a solution which had been in contact with 

 manganese dioxide had yielded a 664 m/x band on treatment with 

 antimony trichloride. Since wald had shown that this is a test for 

 retinene^, *the old observations slipped into a pattern.' ball, 

 GOODWIN and morton (1948) therefore dissolved vitamin A concen- 

 trates in light petroleum, added manganese dioxide and allowed the 

 mixture to stand 6-10 days in darkness. Almost quantitative yields 

 of a substance giving the same colour reaction (A^^^x = 664 m// 

 with antimony trichloride reagent) as retinene^ were obtained. They 

 crystaUized the synthetic retinene (m.p. 61-62°C) and on analysis 

 found C 84-2 per cent, H 9*76 per cent; molecular weight 236 

 (C19H27CHO requires C 84-5, H 9-85 per cent, mol. wt. 284). Deriva- 

 tives of retinene (the 2,4 dinitrophenylhydrazone, the semicarbazone 

 and the hydrazone) were prepared, and these analysed according to 

 expectations though (as in the case of synthetic retinene itself) the 

 molecular weights — determined by depression of freezing point of 

 camphene using Rast's micro method — were rather low. 



THE RELATIONSHIP BETWEEN RETINENE^ 

 AND INDICATOR YELLOW 



Synthetic retinenej, prepared by oxidizing vitamin A^ to its 

 aldehyde by manganese dioxide (ball, goodwin and morton, 



104 



