3i8 CAROTENOIDS OF UNCERTAIN STRUCTURE XIV 



at 514.5 and 481 m/^ in carbon disulphide) , the chromatographic behaviour, the 

 blue colouration with concentrated hydrochloric acid, and the melting point 

 all indicate a close relationship to, or even identity with, antheraxanthin 

 (cf. p. 191). The two pigments can, however, be chromatographically separated, 

 antheraxanthin being found in the upper zone. This behaviour is reminiscent 

 of the pair of isomers, flavoxanthin and chrysanthemaxanthin. These two 

 pigments also have closely similar properties but can be separated on a zinc 

 carbonate chromatogram, and also differ in their reaction with hydrochloric 

 acid, only flavoxanthin giving a blue colouration (cf. p. 210). The blue colour- 

 ation produced on shaking an ethereal solution of petaloxanthin with concen- 

 trated aqueous hydrochloric acid is weaker than the colouration produced with 

 antheraxanthin. 



The nature of the three oxygen atoms present in petaloxanthin is also 

 unknown. The strong adsorption of the pigment on calcium carbonate suggests 

 that it contains two hydroxyl groups. The presence of a third hydroxyl group 

 is unlikely, since a compound containing three hydroxyl groups should be moie 

 strongly adsorbed than antheraxanthin which contains 2 hydroxyl and one 

 epoxide group. A re-investigation of petaloxanthin thus appears very desirable. 



Properties 



Crystalline form: The pigment crystallises from a mixture of carbon di- 

 sulphide and petroleum ether in long, spear-like crystals. From ethanol it is 

 obtained in silky, lustrous, light-yellow leaflets which appear under the micro- 

 scope as long, thin, straw-yellow squares. (A microphotograph will be found in 

 the communication by Zechmeister and co-workers^^). 



Solubility: Petaloxanthin is easily soluble in benzene, less easily soluble in 

 carbon disulphide, sparingly soluble in cold ethanol and almost insoluble in 

 petroleum ether and petrol. 



Melting point: 211-212° (corr., oil-bath), 202° (Berl-Block, short thermo- 

 meter). 



Spectral properties: 



Solvent Absorption maxima 



Carbon disulphide 514.5 481 m/z 



Chloroform 492 460.5 m/t 



Benzene 494 460.5 m/z 



Ethanol 483 451.5 m/i 



Optical activity: No data are available. 



Partition test: Petaloxanthin is entirely hypophasic. 



Chromatographic behaviour: The pigment is well adsorbed on calcium 

 carbonate from carbon disulphide solution, or on calcium hydroxide from 

 References p. 341-343. 



