222 CAROTENOIDS CONTAINING CARBONYL GROUPS XII 



Source References 



Selaginella N. A. Monteverde and V. N. Lubimenko, Bull. Acad. 



Sci. Petrograd [6J 7 (1913) 1105. — T. Lippmaa, Ber. hot. 



Ges. 44 (1916) 643. 

 Taxus baccata R. Kuhn and H. Brockmann, Ber. 66 (1933) 828. M. 



TswETT, Compt. rend. 152 (1911) 788. 

 Thuja orientalis L. M. Tswett, Compt. rend. 152 (1911) 788. 



Preparation" 



The ripe japonica fruit are mashed to a fine pulp and extracted with methanol 

 in portions of 10 kg. The first two extracts are usually colourless to light red, and 

 contain hardly any pigment, while the following methanol extracts are deep red in 

 colour. The residue is then extracted with petroleum ether (b.p. 70-80°). The com- 

 bined methanol extracts are diluted with water, and the pigments extracted with 

 petrol. This petrol solution is combined with the petrol extract. Considerable 

 purification of the pigment is achieved by repeated partitioning between methanol 

 and petroleum ether. The last petrol solution is concentrated in vacuum almost to 

 dryness. On cooling, rhodoxanthin crystallises. It is boiled first with a little metha- 

 nol and then with petroleum ether. By this procedure about 70 mg of crude pigment 

 are obtained Irom 10 kg of japonica fruit. 



Rhodoxanthin is purified by recrystallisation from a mixtur^of one part of 

 benzene and four parts of methanol, or by slowly evaporating an ethanol solution. 



Chemical Constitution 

 CH, CH, CH, CH., 



C CHo CH3 CH3 CH3 C 



/\ I I I I /\ 



CHa C=CHCH=C-CH = CHCH = C-CH=CHCH=CH-C=CHCH=CH-C=CHCH = C CHj 



0=C C-CHg HgC-C C=0 



\ /" Rhodoxanthin X / 



CH CH 



The constitution of rhodoxanthin was elucidated by Kuhn and Brock- 

 MANN^'. Elementary analysis gave the molecular formula C^qYIc^qO^. On catalytic 

 hydrogenation the pigment first rapidly absorbs 12 mols of hydrogen ; a further 

 2 mols are taken up on prolonged hydrogenation. This behaviour indicates the 

 presence of 12 double bonds and two carbonyl groups. The presence of the 

 latter was confirmed by the preparation of a dioxime, but whereas polyene 

 aldehydes (e.g. lycopenal) react readily with hydroxylamine, rhodoxanthin 

 only reacts with difficulty. For this reason, Kuhn and Brockmann concluded 

 that two ketone groups are present in the pigment molecule, conjugated with 

 the system of conjugated double bonds. This conclusion is in accord with the 

 long-wavelength location of the absorption bands. 



By means of chromic acid oxidation, Kuhn and Brockmann^" established 

 the presence of six side-chain methyl groups. 

 References p. 253—255, 



