3 ^-CAROTENE 139 



DiJiydroxy semi-P-carotenone C^^Yi^^O^ : 



C OH CH, CH3 CHg CH3 C 



/\/ II I I /\ 



CH, C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-CO CH. 



II I 



CHj C-OH HgC-CO CHg 



\ /\ Dihydroxysemi-j5-carotenone \^ / 



CH2I CHj 



CH3 



Dihydroxysemi-^-carotenone is prepared by the oxidation of dihydroxy- 

 /3-carotene with o.i N chromic acid^^®. The pigment ciystalUses from a mixture 

 of benzene and petroleum ether in dark red prisms with a bluish lustre, m.p. 

 172°. It is readily soluble in chloroform, somewhat less soluble in benzene and 

 ethanol and hardly soluble in petroleum ether. Dihydroxysemi-jS-carotenone 

 is hypophasic in the partition test. 



Solvent: Absorption maxima: 



Carbon disulphide 534 495 464 m// 



Petroleum ether 497 468 440 m;^ 



Benzene 512 481 452 m/i 



Ethanol (498) (471) m^u 



Chloroform 510 479 452 m/i 



Sem,i-^-carotenone C40H56O2 : 



CHo CHo CHo CHo 



C CHo CHo CHo CHo C 



/\ I I I I /\ 



CH2 C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-CO CH, 



I 



Hg C'GH3 H3C'C0 CH2 



\ / Semi-^-carotenone \^ / 



CH2 CH2 



Semi-j8-carotenone was prepared by Kuhn and Brockmann^" by the 

 oxidation of ^-carotene with o.i N chromic acid. It is also formed on treating 

 a solution of dihydroxy-j3-carotene in benzene with lead tetra-acetate in glacial 

 acetic acid^^*. It crystallises from methanol in square, scarlet plates, m.p. 

 ii8-iig° (corr., evacuated capillary). Semi-^-carotenone is fairly soluble in 

 petroleum ether and less soluble in ethanol. It is epiphasic in the partition test. 

 For further information, cf. Kuhn and Brockmann^^'. 



Solvent: Absorption maxima: 



" Carbon disulphide 538 499 m/z 



Chloroform (519) (487) m^ (diffuse) 



Petroleum ether 501 470 446 m^ 



Benzene 518 486 458 van 



Hexane 500 469 443 m/< 



References p. 165-iyo. 



