248 CAROTENOIDS CONTAINING CARBONYL GROUPS XII 



It is hardly soluble in petrol, but somewhat more soluble in methanol, benzene 

 and carbon disulphide. 



Solvent Absorption maxima 



Capsylaldehyde /3-Carotenone aldehyde 



Carbon disulphide . . 491 459 430 m/z 490 459 430 m/x 



Benzene 476 446 420 vajj, 478 448 421 m/x 



Hexane 458 431 m// 458 431 m/x 



4-Hydroxy-p-caroteno7ie aldehyde C27H3e04®* : 

 CHo CHo 



\V 



/\ I I I 



CH2 OC-CH=CH-C=CHCH=CH-C=CHCH=CHCH=C-CH=CH-CHO 



HOCH OC-CHa 



\ y/ 4-Hydroxy-)3-carotenone aldehyde 



CHa 



This aldehyde is formed besides capsylaldehyde and capsanthylal by the 

 chromic acid oxidation of capsanthin diacetate. Only the oxime has so far 

 been obtained in the crystalline state. It forms yellow cigar-shaped crystals, 

 m.p. 189° (corr.). The oxime is readily soluble in benzene, methanol, hot petrol 

 and hot hexane, but only sparingly in carbon disulphide. The absorption 

 spectrum of the aldehyde coincides with that of the oxime, and is hardly 

 different from that of capsylaldehyde. 



Solvent Absorption maxima 



Carbon disulphide 490.5 459.5 429 m/z 



Benzene 477 449 420 m/< 



Hexane 459 433 408 m/i 



Zechmeister and von Cholnoky^^ subjected capsanthin to a different 

 kind of degradation, namely hydrolysis with aqueous alcoholic sodium hydro- 

 xide in a sealed tube. The product obtained in this way was identified with 

 citraurin (cf. p. 219), and the structures of both pigments were thus confirmed. 



Cis-Trans Isomers 



As early as 1937, Zechmeister and von Cholnoky^^ observed that pure 

 capsanthin forms 2 zones in the chromatogram. This observation was hrst 

 explained as due to the formation of the enol form of the pigments. These 

 investigations were continued by the same two authors in 1940, and it was 

 found that not only 2, but several zones appeared on the adsorption column^*"'. 

 Following the investigations by Gillam and El Ridi^"^ and Zechmeister and 

 co-workers^"2^ the phenomenon was then ascribed to cis-trans isomerisation. 

 References p. 253-255. 



