538 VI. CAROTENOIDS AND RELATED COMPOUNDS 



((/) Semi-a-carotenone, C40H56O2. When a-carotene is oxidized with 

 chromic acid, this diketone is one of the products formed. Semi-a-carote- 

 none crystalhzes from ethanol in needles which melt at 135°C. It 

 possesses no biological activity as a provitamin A. It forms a monoxime, 

 C40HB7O2N, which is a red crystalline product melting at 132°C. '^^ Accord- 

 ing to Karrer and co-workers,'*^ semi-a-carotenone has the following for- 

 mula: 



HsC CH3 HjC CHj 



Q CHj CH3 CHj CHj c 



/\ hh|hhhIhhhhIhhhIhhh/\ 

 H2C C-c:c-C:C-c;C-C:C'C:C-C;C-C:C'C:C'C:C-C GHz 



I % II 



HjC = C CHj 



\ / \ / % / 



C CHj HjC C 



Ht H 



Semi-a-carotenone 



(e) a-Apo-2-carotenal, C30H40O. On permanganate oxidation of a- 

 carotene, an aldehyde having 10 less carbons than the original hydrocarbon 

 is formed. The rupture in the hydrocarbon chain takes place between car- 

 bons 7 and 8. The /3-ionone residue is destroyed and the a-ionone ring is 

 attached to the polyene chain. a-Apo-2-carotenal crystallizes from petro- 

 leum ether in bright red prisms which melt at 158°C. In general, this 

 compound is less soluble than the corresponding j8-isomer. 



HjC CHj 



Q CHj CHj CHj CHj 



/\hhh Ihhh Ihhhh IhhhI h 

 HzC C'C:c-c:c-c:C'C:C'C:C-C:C'C:C'C:C' C=0 



I I 



HjC C 



\ ^ \ 



C CHj 



H 



a-Apo-2-carotenal 



(/) a-Apo-2-carotenol , C30H42O. The alcohol, corresponding to the apo- 

 aldehyde, is formed when the latter substance is treated with aluminum 

 isopropoxide in isopropanol. It yields spherical concavities lined with 

 golden-yellow crystals which melt at 157°C. 



HjC CHj 



C CHj CHj CHj CHj 



/\hhh Ihhh Ihhhh Ihhh I 

 HzC C-c:c-c:c-c:c-c:c-c:c-C;C-C:c-C:g- ch,oh 



I I 



HjC C 



\ ^ \ 



C CHj 



H 



af-Apo-2-carotenol 



'85 p, Karrer and U. Solmssen, Helv, Chim, Acta, 18, 25-27 (1935). 



