262 CAROTENOID CARBOXYLIC ACIDS XIII 



Solvent Absorption maxima 



Carbon disulphide 527.5 492 457.5 m^ 



Chloroform 509 474,5 442 m/i 



On adding alkali to a suspension of stable norbixin in water, it is converted 

 into a very sparingly soluble, crystalline yellow salt. The action of diazomethane 

 on norbixin yields a stable methylbixin. Trans-norhixm. is stable in air. It 

 dissolves in concentrated sulphuric acid with a greenish-blue colour. 



Stable bixin, the monom,ethyl ester of stable norbixin C25H30O4: 

 Karrer and co-workers^* obtained stable bixin by allowing labile natural 

 bixin to stand in chloroform solution in the presence of iodine. It crystallises 

 from acetic acid or pyridine, or from acetone in flakes. M.p. 216-217° (uncorr., 

 with decomposition). The solubility in organic solvents is considerably smaller 

 than that of labile bixin. 



Solvent Absorption maxima 



Carbon disulphide 526.5 491 457 mfi 



Chloroform 509.5 475 443 m^ 



(of. Fig. 17, p. 355) 



On shaking a solution of stable bixin in acetic acid and pyridine with zinc 

 dust for a short time, dihydrobixin is obtained. The same dihydrobixin is also 

 formed from labile bixin^" under the same conditions. 



Stable methylbixin, the dimethyl ester of stable norbixin CjgHjjO^: 



Stable methylbixin can be prepared either by the isomerisation of labile 



methylbixin in the presence of iodine^"- ^^ or by the esterification of stable 



norbixin. The ester is also formed by shaking in air a solution of dihydro- 



methylbixin in piperidine, or in pyridine containing a little sodium hydroxide^^. 



CI13 CH3 CH3 CHj 



HjCOOC- CH=CH- C=CHCH=CH- C=CHCH=CHCH=C- CH=CHCH=C- CH=CH- COOCH, 



Stable methylbixin 



Stable methylbixin crystallises from a mixture of chloroform and ethanol 

 in stout, blue- violet needles, m.p. 205-206° (corr.). On shaking a solution in 

 pyridine containing a little acetic acid with zinc dust at 50°, the same dihydro- 

 methylbixin is obtained as from labile methylbixin. 



Solvent Absorption maxima 



Carbon disulphide . . . 525.5 490 456.5 m/z 



Chloroform 509.5 475.5 444 m^ 



Hexane 484 450 425 405 m/z (cf. Fig. 19, p. 356) 



References p. 290-294. 



