284 CAROTENOID CARBOXYLIC ACIDS XIII 



Properties 



Crystalline form: Azafrin crystallises from benzene in microscopic orange- 

 red needles combined into clusters. From toluene it crystallises in prisms. 



Melting point: 212-214° (corr.). 



Solubility: The pigment is insoluble in water, but dissolves in dilute alkali 

 or alkali carbonate solutions. Azafrin is fairly soluble in chloroform, ethanol, 

 acetic acid and benzene, but only very sparingly in ether. 



Solvent Absorption maxima 



Chloroform 458 428 m/z 



Pyridine 458 428 m/i 



Sodium hydroxide 447 422 m/z 



Optical activity: [a-Y^^^^^ = — 75° (in ethanol, c = 0.28). The optical rotation 

 is not appreciably altered by the addition of boric acid^^^. 



Colour reactions*: Azafrin dissolves in concentrated sulphuric acid with an 

 intense blue colour which changes to violet on addition of alcohol. On dissolving 

 the pigment in acetic acid and adding concentrated hydrochloric acid, a violet 

 colouration is produced after short boiling or on standing for several hours. 

 On passing hydrogen chloride into a saturated chloroform solution, the latter 

 assumes a cornflower-blue colour. Antimony trichloride in chloroform solution 

 produces an emerald green colouration which changes into blue. 



Partition test: Azafrin exhibits entirely hypophasic properties. 



Chromatographic behaviour: Azafrin can be chromatographed on calcium 

 carbonate from benzene-petrol solution. The chromatogram is developed with 

 benzene. A mixture of benzene and methanol, or of pyridine and methanol is 

 used for elution^^^. 



Derivatives 



Azafrinone €371^3304 (Formula p. 283): 



KuHN and Deutsch^^^ obtained azafrinone by the oxidation of azafrin in 

 acetic acid and benzene with o.i N chromic acid solution. The diketone can also 

 be prepared by the saponification of azafrinone methyl ester^®^. It separates 

 from acetone in orange-red plates or needles, m.p. 191° (corr.). On catalytic 

 hydrogenation, azafrinone absorbs 9 mols of hydrogen. Azafrinone is optically 

 inactive. 



* R. KuHN, A. WiNTERSTEiN and H. Roth compare the colour reactions of azafrin, 

 crocetin and norbixin, Ber. 64 (1931) 333. 



References p. 2go-2g4. 



