172 CAROTENOIDS CONTAINING HYDROXYL GROUPS XI 



two pigments contain identical chromophoric systems. The oxygen is present 

 in the form of a hydroxyl group which can be acetylated. The position of 

 the hydroxyl group has not been established, but it is probably at carbon atom 

 3 by analogy with other phytoxanthins (cf. Karrer and co-workers^) . 



Properties 



Lycoxanthin crystallises from a mixture of benzene and petroleum ether in 

 jagged or circular reddish-brown plates. From carbon disulphide, the pigment 

 is obtained in violet needles, m.p. i68° (corr.). Lycoxanthin is easily soluble in 

 carbon disulphide and benzene, somewhat less easily in petroleum ether, and 

 only very sparingly in ethanol. On partition between methanol and petroleum 

 ether it behaves in the same way as cryptoxanthin and rubixanthin. It can 

 only be adsorbed on calcium carbonate from petroleum ether solution, whereas 

 it can be adsorbed on calcium hydroxide and aluminium oxide from benzene 

 solution. 



Solvent: Absorption maxima: 



Carbon disulphide 546 506 472 m;u 



Petroleum ether 504 473 444 myw 



Benzene 521 487 456 m/z 



Ethanol 505 474 444 m// 



On shaking an ethereal solution of lycoxanthin with concentrated hydro- 

 chloric acid, no blue colouration is observed. 



The monoacetate of lycoxanthin is formed by treating lycoxanthin with 

 acetyl chloride in pyridine. The monoacetate crystallised from a mixture of 

 benzene and methanol in violet-red needles, m.p. 137° (corr.). 



The acetate is easily soluble in carbon disulphide but only sparingly soluble 

 in ethanol and petroleum ether. Its absorption spectrum is identical with that 

 of lycoxanthin. 



2. RUBIXANTHIN C4oH5gO 



History 



1934 KuHN and Grundmann^ discover a pigment isomeric with cryptoxanthin 

 amongst the pigments of Rosa rubiginosa. They propose the name rubi- 

 xanthin and propose a constitutional formula. 



Occurrence 



Rubixanthin is one of the polyene pigments which are not widely distributed 

 in nature. It occurs mainly in different species of roses. 

 References p. 214—212. 



