314 CAROTENOIDS OF UNCERTAIN STRUCTURE XIV 



and ozonisation yields 0.85 mols of acetone. On the basis of these results 

 Zechmeister and Schroeder proposed the above formula for gazaniaxanthin. 

 Apart from the uncertainty regarding the position of the hydroxyl group, this 

 formula partly contradicts the experimental results. According to all previous 

 experience in the carotenoid series, acetone is only obtained on ozonisation in 

 the presence of an isopropylidene grouping (CH3)2C = C ... It is not easy to see 

 why the grouping (CH3)2CH2... should also give rise to nearly i mol (0.85) 

 of acetone on ozonisation. (Zechmeister and Schroeder^' cite the analogous 

 case of thymol which on ozonisation yields 0.3 mols of acetone). Further 

 experimental study is clearly required for a complete elucidation of the consti- 

 tution of gazaniaxanthin. 



Properties 



Gazaniaxanthin crystallises from a mixture of benzene and methanol in 

 glistening red plates, m.p. 133-134°. It is found below rubixanthin but above 

 cryptoxanthin in the chromatogram on calcium hydroxide. It shows the same 

 behaviour in the partition test as other phytoxanthins containing a hydroxyl 

 group. 



Solvent Absorption maxima 



Carbon disulphide 531 494.5 461 m/n 



Benzene 509 476 447.5 m/i 



Petroleum ether 494.5 462.5 434.5 m/j, 



Ethanol 494.5 462 434.5 m/i 



According to the experiments of Zechmeister and Schroeder*', gazania- 

 xanthin exhibits no vitamin A activity. It may be concluded from this result 

 that the hydroxyl group is substituted in the ^-ionone ring. 



Ga "an iaxanth in monoacetate: 



This compound is formed by treating gazaniaxanthin with acetic anhydride 

 in pyridine. It crystallises from benzene or methanol in stout needles and from 

 a mixture of petroleum ether and methanol in curved needles, m.p. 83-85°. 

 The spectral properties correspond to those of gazaniaxanthin. 



Cis-trans Isomers 



Zechmeister and Schroeder*' converted gazaniaxanthin into a complex 

 mixture of isomers by the usual methods (p. 39). So far it has not been possible 

 to obtain these compounds in a crystalline state and to investigate them in 

 detail. 

 References p. 341-343. 



