302 CAROTENOIDS OF UNCERTAIN STRUCTURE XIV 



ethylenic double bonds exhibit a different behaviour (cf. p. 56). The test for 

 the presence of an isopropylidene grouping gave a negative result, thus excluding 

 a y-carotene type structure. On permanganate degradation, almost 5 (4.77) 

 mols of acetic acid were obtained. This result is not in contradiction with the 

 proposed formula for aphanin since cryptoxanthin, which contains six side- 

 chain methyl groups, also gives rise to only 4.85 mols of acetic acid^^. The 

 reduction of aphanin with aluminium isopropoxide and isopropylalcohol 

 yielded an alcohol, aphanol, with an absorption maximum displaced by about 

 10 vafx towards shorter wavelengths as compared with aphanin (in petrol). 

 TiscHER suggested that the structure of aphanol is identical with that of 

 cryptoxanthin. If this suggestion is correct, the carbonyl group must be in the 

 3'-position, but since aphanol was not obtained crystalline and was not analysed, 

 this question must still remain open. 



In animal feeding tests, aphanin exhibits half the vitamin A activity of 

 ^-carotene, so that it must contain one unsubstituted /3-ionone ring according 

 to present views. For that reason the constitution of one half of the molecule 

 must be assumed to correspond to that of j3-carotene. The fact that the pigment 

 is optically inactive is also in agreement with the proposed formula. 



Properties 



Crystalline form: Aphanin crystallises from a mixture of benzene and 

 methanol in large, spear-like, blue-black leaflets which are often combined in 

 rosettes and exhibit a pronounced graphitic lustre. From a mixture of benzene 

 and petrol, aphanin is obtained in stout prismatic crystals. 



Melting point: 176° (corr., crystallised from benzene-methanoP^). 180° 

 (corr., crystallised from benzene-petrol^"). 



Solubility: Aphanin is very readily soluble in carbon disulphide, chloroform 

 and benzene, less readily soluble in pyridine, ether and petrol, and very sparingly 

 soluble in methanol. 



Spectral properties: 



Solvent Absorption range Absorption maxima 



Carbon disulphide . 475-555 533.5 494 m/t 



Chloroform .... 455-520 504 474 m^ 



Benzene 455-520 505 472 m/i 



Petrol, b. p. 70-80° . 445-510 494 460 m/i 



Pyridine 460-525 507.5 477 m/i 



Methanol 445-505 491.5 457 m// 



TiscHER^^ describes the absorption spectrum of aphanin as follows: "The 

 absorption spectrum exhibits two maxima separated by a more weakly ab- 

 References p. 341-343. 



