I ^-CITRAURIN 219 



Chemical Constitution 



Cxlq Cliq 



\V 



/\ I I II 



CH, C-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CHCH=C-CHO 



I II 



HOCH C-CHs 



\ / /9-Citraurin 



The composition of /S-citraurin (C30H40O2) , and the ease of oximation which 

 suggests the presence of an aldehyde group, led Zechmeister and Tuzson^ 

 to suggest that this pigment represents a degradation product of a C40 caro- 

 tenoid. Karrer and Solmssen^ established the very close relationship between 

 /S-citraurin and j3-apo-2-carotenaP. They proposed the formula shown above, 

 according to which ^-citraurin is a 3-hydroxy-j3-apo-2-carotenal. The correct- 

 ness of this formula was later established by Karrer and co-workers* and by 

 Zechmeister and von Cholnoky^. The first-named authors obtained ^-citraurin 

 by the permanganate degradation of zeaxanthin (cf. p. 184), while Zechmeister 

 and von Cholnoky obtained the aldehyde by the hydrolysis of capsanthin 

 (cf. p. 248). j3-Citraurin can also be prepared, though only in small amounts 

 accompanied by a large proportion of a-citraurin, by the permanganate degra- 

 dation of xanthophyll^. Finally, Karrer and Koenig' also succeeded in ob- 

 taining the aldehyde by permanganate oxidation of capsanthin. 



Properties 



Crystalline form: /3-Citraurin crystallises from a mixture of benzene and 

 petrol in very thin, yellow to orange plates which appear almost colourless 

 under the microscope. 



Melting -point: 147° (corr., Berl-block, short thermometer). 



Solubility: j3-Citraurin dissolves easily in acetone, ethanol, ether, benzene 

 and carbon disulphide. The solubility in petrol is very small, even at the boiling 

 point. 



Spectral properties: 



Solvent Absorption maxima 



Carbon disulphide 525 490 457 m^u (diffuse) 



Benzene 497 467 m^u 



Petrol 488 459 m/i (sharp) 



Hexane 487 458 m/i 



Ethanol diffuse 



Solutions of the pigment in carbon disulphide have a beautiful red colour. 

 Ethanol solutions are red, hexane and petrol solutions straw yellow, and benzene 

 solutions yellowish-brown. 



References p. 253-255. 



