224 CAROTENOIDS CONTAINING CARBONYL GROUPS XII 



the latter is coloured a faint red- violet. With more concentrated acid the 

 colouration is somewhat more intense. 



Partition test: On partitioning between petroleum ether and 90 % methanol, 

 rhodoxanthin colours both layers. 



Chromatographic behaviour: In contrast to phytoxanthins, rhodoxanthin is 

 not adsorbed on calcium carbonate. It is well adsorbed on alumina from a 

 mixture of benzene and petrol. It forms a deep violet zone in the chromatogram 

 and can be eluted with a mixture of petrol and methanol. 



Detection and estimation. After separation from other carotenoids by means 

 of chromatographic analysis on alumina, rhodoxanthin can be identified by 

 its absorption spectrum. 



Chemical behaviour: Rhodoxanthin is relatively stable towards atmospheric 

 oxygen. 



Derivatives 

 Rhodoxanthin dioxvme C40H52O2N2 : 



The dioxime is prepared by boiling a solution of rhodoxanthin in a little 

 pyridine with a solution of 6 mols of hydroxylamine containing some sodium 

 hydroxide". The dioxime crystallises from a mixture of pyridine and petrol 

 in red squares, m.p. 227-228° (corr., evacuated capillary). Rhodoxanthin 

 dioxime is less easily soluble in petrol and benzene, but more soluble in ethanol 

 than rhodoxanthin. In contrast to the latter, it can be adsorbed on calcium 

 carbonate from petrol. On alumina it is adsorbed so strongly that it cannot 

 be eluted. 



Solvent Absorption maxima 



Carbon disulphide 516 483 453 m^ 



Chloroform 527 490 457 vcifi 



Benzene 527 490 457 m/i 



Ethanol 516 483 454 mix 



Petrol 516 483 453 m/^ 



Hexane 513 479 451 m/^ 



Petroleum ether 510 477 450 m/^ 



Dihydrorhodoxanthin C4QH52O2: 



CH, CH, CH, CH, 



C CH3 CH3 CII3 £'1x3 G 



/\ II I I /\ 

 CH„ C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CH=CH-C CHg 



I II II I 



0=C C-CHg H3C-C C=0 



\ / Dih3'drorhodoxanthin \^ ^Z 



CHa CHa 

 References p. 2^3—253. 



