I BIXIN 269 



By brief shaking of a solution of labile methylbixin in pyridine with acetic 

 acid and zinc dust, Kuhn and Winterstein'^ obtained dihydromethylbixin. 

 Karrer and Takahashi^^ found that by the saponification of labile methyl 

 bixin with ethanolic sodium hydroxide (i mol) at 65°, stable bixin is formed 

 besides labile bixin. Labile methylbixin dissolves in concentrated sulphuric 

 acid with an intense blue colour. 



Dihydromethylbixin CggHg^O^ : 



This compound is obtained by briefly shaking a solution of labile or stable 

 methylbixin in pyridine and acetic acid with zinc dust". It crystallises in orange 

 yellow leaflets, m.p. 180-182° (corr.). A piperidine solution of dihydromethyl 

 bixin oxidises in air to give stable methylbixin''^. (For constitution, see p. 265). 



Solvent Absorption maxima 



Carbon disulphide 454 428 m/z 



Chloroform 435 410 m/n 



(of. Fig. 20, p. 356) 



Perhydronorbixin dimethyl ester, perhydromethylbixin CjgHjoO^: 

 Perhydromethylbixin was prepared by Herzig and Faltis by the catalytic 

 hydrogenation of labile methylbixin'^^. It is also obtained by the methylation 

 of perhydronorbixin with diazomethane, or with methanol and hydrogen 

 chloride''^. Karrer and co-workers^" methylated perhydrobixin to the dimethyl 

 ester by treatment with dimethylsulphate and aqueous potassium hydroxide 

 in acetone. B.p. 2ii°/o.3 mm. D^° 0.9234; n^° 1.456881. By heating with sodium 

 and amyl alcohol, perhydromethylbixin is converted into 4:8:13: 17-tetra- 

 methyleicosane-i : 20-dioF2. 



Perhydronorbixin diethyl ester C23H54O4: 



The total synthesis of this ester by Karrer and co-workers^^ has already 

 been mentioned (p. 259). The compound is a colourless oil, b.p. 20770.3 mm. 



Perhydronorbixin diamide C24H48O2N2 : 



Perhydronorbixin is converted into the acid chloride by means of phos- 

 phorous pentachloride or thionyl chloride and the acid chloride is treated with 

 concentrated aqueous ammonia^*. The diamide separates from ethyl acetate 

 or ether in colourless crystals, m.p. 111°. It is almost insoluble in ether but 

 soluble in ethanol and chloroform. 



Perhydronorbixin bis-( 2:4:6-tribromoanilide) C33H5o02N2Br5 : 



The acid chloride of perhydronorbixin (see above) is reacted with 2:4:6- 

 tribromoaniline^^ and the product is recr^'stallised from methyl acetate. 

 The tribromanilide melts at 83°. 

 References p. 2go-2g4. 



