202 CAROTENOIDS CONTAINING HYDROXYL GROUPS XI 



4', since only these will explain the formation of a:a-dimethylsuccinic acid and 

 the absence of a:a-dimethylglutaric acid on oxidation. 



The spectral properties of xanthophyll indicate a resemblance to a-carotene. 

 NiLSSON and Karrer^^* converted perhydroxanthophyll into the dibromide 

 and then removed the two bromine atoms by reductive fission. The perhydro- 

 carotene C40H78 formed was optically active and the rotation had the same sign 

 and was of the same magnitude as that of the perhydrocarotene obtained by 

 the reduction of a-carotene. Hence xanthophyll is a dihydroxy-a-carotene. 

 These investigations also proved that the hydroxyl group must occupy position 

 3 ' in the a-ionone ring, since a hydroxyl group on carbon atom 4' would have 

 enolic character. 



Very recently Karrer, Koenig and Solmssen^^^ succeeded in isolating 

 a-citraurin, an isomer of /5-citraurin discovered by Zechmeister and Tuzson^^^, 

 by the careful potassium permanganate degradation of xanthophyll. The 

 formula of xanthophyll was thus further confirmed. 



CHo CHo 



\V 



C CHo CHo CHo CHo 



/\ I I I I 



CHa C- CH=CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CHCH=C- CHO 



I I! 



HOCH C-CHs 



\^ / ^-Citraurin 



CH2 



CHo CHo 



\/ 



C CH, CH, CH, CH, 



/\ I I I I 



CHj CH- CH = CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CHCH=C- CHO 



HOCH C-CH3 



\ /^ ' a-Citraurin 



CH 



'Properties and Physical Constants 



Crystalline form: The pigment crystallises from methanol in violet prisms 

 which have a metallic lustre and characteristic dovetail shape. The crystals 

 contain one molecule of methanol of crystallisation. 

 References p. 214-217. 



