8 XANTHOPHYLL iq-j 



The empirical formula of auroxanthin was determined by Karrer and 

 RuTSCHMANN^*'. The number of double bonds was determined by catalytic 

 hydrogenation. The position of the absorption bands (454, 423 m^ in carbon 

 disulphide) indicated the presence of seven conjugated double bonds. Zerewiti- 

 NOFF determinations gave values corresponding to two or three active hydrogen 

 atoms. Since the determination of active hydrogen in xanthophyll, however, 

 gave values corresponding to 2.5 active hydrogen atoms, it could be assumed 

 that auroxanthin contains only two hydroxyl groups. The nature of the other 

 two oxygen atoms could not at first be established. However, when auro- 

 xanthin, together with mutatoxanthin and a little zeaxanthin had been obtained 

 by the acid treatment of violaxanthin^^, a connection between these pigments 

 was clearly indicated. 



The nature of this relationship was elucidated by the investigations of 

 Karrer and Jucker in the course of which violaxanthin was identified as 

 zeaxanthin di-epoxide (cf. p. 195) and auroxanthin as the corresponding 

 di-furanoid oxide^^. The proposed formula of auroxanthin is in complete agree- 

 ment with all the properties of the compound. The configurations of natural 

 and partially synthetic auroxanthin appear to be the same^^. 



Properties 



Auroxanthin crystallises from methanol in golden-yellow needles m.p. 203° 

 (uncorr., evacuated capillary). The solubility of the pigment is very similar to 

 that of violaxanthin. The pigment shows no optical rotation in benzene solution. 



A characteristic test for auroxanthin is the blue colouration which is ob- 

 served on shaking an ethereal solution with 15 % hydrochloric acid. This blue 

 colouration is very stable. In carbon disulphide, auroxanthin shows absorption 

 maxima at 454 and 423 m^ (cf. Fig. 10, p. 351). 



8. xanthophyll C4oH5g02* 

 History 



1837 Berzelius^^ coins the term "xanthophyll" for the yellow pigment of 



autumn leaves. 

 1907 WiLLSTATTER and MiEG^^ isolate xanthophyll from green leaves in the 



crystalline state and determine its empirical formula and its molecular 



weight. 



There is no uniformity in the Uterature regarding the designation of this compound. 

 Some investigators employ the term "lutein" proposed by Kuhn, and use the term xantho- 

 phyll only as a generic term for hydroxyl-containing carotenoids, for which Karrer 

 proposed the term phytoxanthins. In this monograph the name xanthophyll is retained 

 for the yellow leaf pigment C^oHggOg. 



References p. 214— 2iy. ^ 



