CAROTENOIDS WITH LESS THAN FORTY CARBON ATOMS 601 



to elucidate the structure of this pigment. More recent studies of Kuhn 

 and his collaborators^^^ have succeeded in clarifying the structure of this 

 dyestuiT. 



a. Structure. Azafrin, C27H38O4, absorbs seven molecules of hydrogen 

 on catalytic liydrogenation, forming perliydro-azafrin, C27H52O4. The 

 latter is a colorless, odorless, viscous oil which can be distilled unchanged in 

 vacuo. When it is treated with bromine in chloroform, only four double 

 bonds of the azafranillo dyestuff are saturated. On treatment with iodine 

 in benzene, a greenish black, crystalline iodide is formed. Of the four 

 oxygen atoms in azafrin, two are present in the carboxyl group. This is 

 evident from the fact that, when titrated with thymol blue in alcohol, aza- 

 frin titrates as a monocarboxylic acid. Perhydro-azafrin behaves in a 

 similar manner. Since the Zerewitinoff test shows the presence of three 

 active hydrogens, it is evident that the other two oxygens are present as 

 hydroxyl groups. Kuhn and Deutsch^^^ proved that the hydroxyl groups 

 are on adjacent carbons and represent, in fact, a ditertiary glycol. On 

 oxidation with chromic acid, azafrinone is formed, which is a diketone. 

 Since azafrinone is optically inactive, it is evident that the optical activity 

 of the azafrin resides in the alcoholic hydroxyl groups. Kuhn and Deutsch*'^ 

 have assigned to azafrin the formula shown here. 



CH3 CHj CH3 



H5C CHj 



/\/HH I HHH I HHHH I HH || 



HaC c-c:c-c:c-c:c-c:c-c:c-c:c-C:C'COH 



I I 



HjC c — oh 

 \ / \ 



C CH3 



H2 



Azafrin 



b. Occurrence. Azafrin is present in the root and stems of the fig- 

 worts (Sc7'ophulariaceae), Escobedia scabrifolia and E. linearis (ysip- 

 yu).^^2~^^^ These plants grow in tropical America and are used in Para- 

 guay as "azafran" or "azafranillo" for the coloring of fats. The pigment 

 occurs as bright yellow-orange spots in the wood of the roots and stems. 



c. Related Compounds, (a) Azafrin Methyl Ester. Azafrin methyl 

 ester, (HO)2C26H35COOCH3, has the same relation to azafrin as methylcro- 

 cetin to crocetin or as methylbixin to bixin. It can be prepared by dissolv- 

 ing azafrin in 0. 1 iV alkali and treating it with dimethyl sulfate, keeping the 

 reaction slightly alkaline. The methyl ester forms glistening platelets 

 (from methyl alcohol) w^hich melt at 193°C. The ester is insoluble in 

 alkali, but soluble in most solvents, with the exception of petroleum 

 ether; it dissolves exceedingly well in chloroform. The ethyl ester of 

 azafrin ((HO)2C,6H35-COOC2H5), m.p. 182°C., is also kno^vn. 



«5 R. Kuhn, A. Winterstein, and H. Roth, Ber., 64, 333-341 (1931). 

 *^« R. Kuhn and A. Deutsch, Ber., 66, 883-892 (1033), 



