a-Apo-2-carotenol C3QH42O: 



a-CAROTENE 157 



C CH, CH3 CH3 CH3 



/\ I I I ■ I 



CH, CH-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH,OH 



I I 



CHg C" CH3 



\ ^ a-Apo-2-carotenol 



CH 

 This alcohol is obtained by the reduction of a-apo-2-carotenal (lower 

 melting form) with isopropyl alcohol and aluminium isopropoxide. It crystallises 

 from a mixture of benzene and petroleum ether in spherical golden-yellow 

 clusters, m.p. 157° (sinters at 150°). 



Solvent: Absorption maxima: 



Carbon disulphide 478 448 vn.pL 



Petroleum ether 446 420 m/z 



Ethanol 448 423 m// 



On treating a solution of a-apo-2-carotenol in chloroform with antimony 

 trichloride, a fairly stable blue colouration with an absorption maximum at 562 vafi, 

 is observed. 



a-Carotene iodide: 



a-Carotene adds two atoms of iodine with the formation of a crystalline 

 di-iodide C40H56I2 (Karrer, Solmssen and Walker)i®^. This iodide exhibits 

 vitamin A activity. With regard to another iodide of ^-carotene, cf. Kuhn 

 and Brockmann^''". 



Neo-a-carotene U and neo-a-carotene W: 



The question of stereoisomerism in a-carotene was examined several years 

 ago by GiLLAM, El Ridi and Kon^'^^. These investigations have been renewed 

 by Zechmeister and Polgar who succeeded in isolating two cis-trans isomers 

 of a-carotene in the crystalline state* ^'^^. Neo-a-carotene U is formed from 

 a-carotene under the influence of heat, or illumination, or treatment with iodine 

 or acids, or by melting the crystals. It is found above a-carotene in the chro- 

 matogram on calcium hydroxide. The pigment crystallises from a mixture of 

 benzene and methanol in orange prisms, m.p. 65° (corr.). Neo-a-carotene U 

 is more soluble in the usual solvents than a-carotene. On treatment with 

 iodine it is partly' transformed into a-carotene. 



Solvent: Absorption maxirna: 



Carbon disulphide 503 470.5 m/i 



Benzene 485.5 453.5 m^ 



Chloroform 485 453 m^ 



Petroleum ether (B.p. 60-70° C) . . . 471.5 441.5 m^i 



The work of L. Zechmeister has recently been confirmed in detail by F. P. Zscheile 

 and co-workers, Arch. Biochem. 5 (1944) 77, 211. 



References p. 165-170. 



