282 CAROTENOID CARBOXYLIC ACIDS XIII 



According to a more recent procedure due to Kuhn and Winterstein^^^, the 

 escobedia roots are first roughly ground, then finely ground in a spherical mill and 

 exhaustively extracted with acetone in a Soxhlet apparatus. The dark brown 

 solution is allowed to stand overnight, filtered to separate gelatinous material, and 

 evaporated to a small volume in vacuum. The liquid residue soon solidifies to a 

 crystalline mass which is filtered after addition of toluene. For further purification, 

 the crude pigment is twice recrystallised from a mixture of acetone and toluene. 

 Azafrin can also be purified by chromatographic adsorption on calcium carbonate 

 from a petrol-benzene mixture. A less wasteful procedure consists of extracting the 

 impurities with petrol from an alkaline solution of azafrin. 



Chemical Constitution 



\V 



C OH CH3 CH3 CHs 



CH2 C- CH=CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CH- COOH 



I I 



CH2 C'CH3 



\ / \ Azafrin^^* 



CHa OH 



The formula of azafrin was proposed by Kuhn and co-workers and is proved 

 by the following facts.' 



Azafrin is a monocyclic carboxylic acid containing 7 double bonds which 

 must be conjugated amongst themselves and with the carboxyl group^^^. The 

 other two oxygen atoms are present in the form of 2 hydroxyl groups. These are 

 tertiary in nature and must occupy neighbouring positions since on treatment 

 with lead tetraacetate according to Criegee^", tetradecahydroazafrin yields 

 a diketone (perhydroazafrinone)^^^: 



CHq CHo 



\V 



C Cxia CHo Clio 



/\ \ \ I 



CHj CO- CH2CH2CHCH2CH2CH2CHCH2CH2CH2CH2CHCH2CH2COOH 



CH, CO-CH, 



Perhydroazafrinone 

 CH2 



On careful oxidation with chromic acid, azafrin yields a diketone which 

 was termed azafrinone by Kuhn and Deutsch^^^. Since this compound is 

 optically inactive, it can be concluded that the rotatory power of azafrin is due 

 to the two hydroxyl-bearing carbon atoms. Azafrinone absorbs at slightly 

 longer wavelengths than azafrin. As the difference is of about the same 

 magnitude as between ^-carotene and ^-semicarotenone (p. 139), it may be 

 concluded that one of the carbonyl groups of azafrinone is in conjugation with 

 the system of conjugated double bonds. 

 References p. 2go-2g4. 



