264 CAROTENOID CARBOXYLIC ACIDS XIII 



The same apo-3-norbixinal methyl ester, m.p. 147° is formed by the con- 

 trolled permanganate oxidation of stable or labile methylbixin (cf. p. 260). 



It forms an oxime, m.p. 188° and a semicarbazone, m.p. 215°. On shaking 

 an ethereal solution of the pigment with concentrated aqueous hydrochloric 

 acid, no Mue colouration is observed. 



Solvent A hsorption maxima 



Carbon disulphide 455 427 m/i 



Petroleum ether 425 m/i 



Ethanol about 440 m/z (cf. Fig. 17, p. 355) 



Absorption maxima of semicarbazone 



Carbon disulphide 472 443 m/i 



Ethanol 449 m// 



Absorption maxima of the oxime 



Carbon disulphide 458 428 m/i 



Petroleum ether 428 408 m/z 



2. Labile norbixin C24H28O4: 



Labile norbixin is obtained by the saponification of labile bixin^^ or of 

 labile methylbixin^'^. It crystallises from acetic acid in stout red needles, m.p. 

 254-255°. Labile norbixin is readily soluble in pyridine, fairly readily soluble 

 in acetic acid, ethanol and methanol, sparingly soluble in chloroform and methyl 

 acetate, and almost insoluble in ether^^. It readily dissolves in aqueous alkalis. 

 Labile norbixin is autoxidisable in air^^. By boiling a solution of the sodium 

 salt with excess ammonia and 2.3 mols of titanium trichloride, Karrer and 

 co-workers^® obtained dihydronorbixin. If a larger proportion of titanium 

 trichloride is used, or on prolonged boiling, tetrahydro- or hexahydro -norbixin 

 is formed. 



On prolonged heating with aqueous potassium hydroxide (less smoothly 

 by employing ethanolic potassium hydroxide), labile norbixin is converted 

 into stable norbixin^®. By boiling with 3 % methanolic hydrochloric acid, 

 Karrer and Takahashi^'' obtained stable methylbixin, whereas labile methyl- 

 bixin is formed by the methylation of labile bixin with diazomethane^^. On 

 methylation of labile norbixin with dimethyl sulfate, labile bixin and labile 

 methylbixin are obtained^^. For the action of chlorine and hydrogen chloride 

 on the pigment, compare the communication of Heiduschka and Riffart*". 

 Labile norbixin dissolves in concentrated sulphuric acid with a blue-green 

 colour*^. 



The mono-potassium salt of labile norbixin is micro-crystalline. It is insoluble 

 in water and sparingly soluble in ethanol. The di-potassium salt forms brown-red 

 needles, readily soluble in water. When moist, it is readily oxidised in air. 

 References p. 2go-2g4. 



