278 CAROTENOID CARBOXYLIC ACIDS XIII 



separation of the two forms depends on the greater solubihty of the labile form 

 in ether. The ester crystallises from methanol in elongated rectangular plates, 

 m.p. 141°. Under the microscope the crystals appear yellow. One part of the 

 labile ester dissolves in 5900 parts of methanol. Its behaviour towards light, 

 iodine, or heat has already been described on p. 273. Reduction with zinc dust 

 and acetic acid in pyridine yields a dihydroderivative which is identical with 

 that obtained from the stable ester. By saponification with warm ethanolic 

 potassium hydroxide, stable crocetin is formed. 



Solvent Absorption maxima 



Petrol 445 422 m/j. 



Chloroform 458 432.5 m/i 



Tricyclocrocetin C22H2404( ?) : 



This compound was obtained by Kuhn and Winterstein^^s jjy ^j^g (jj-y. 

 distillation of stable crocetin dimethyl ester in vacuum, followed by chromato- 

 graphy and saponification. It crystallises from methanol in colourless needles, 

 m.p. 263-264°. On oxidation with chromic acid it yields 2.5 mols of acetic 

 acid. Catalytic hydrogenation shows the presence of 4 double bonds. For the 

 light absorption curve, the original communication should be consulted. 



Perkydrocrocetin dimethyl ester C22H42O4 : 



This perhydro-compound was obtained by Karrer and Salomon by the 

 catalytic reduction of stable crocetin dimethyl ester^^g j|- ^g ^ viscous oil which 

 partly sohdifies in the form of crystals, m.p. 27° ^^''. 



Perhydrocrocetin dimethyl ester boils at 198-210° at i mm and 180-185° at 

 0.05 mm. For the light absorption curve, see the communication by Karrer 

 and Salomon^^i. 



2:6:11 :i§-Tetramethylkexadecane-i:i6-diolC^QH.^202' 



This diol was obtained by Karrer and co-workers^^^ by the reduction of 

 perhydroci ocetin dimethyl ester with sodium in alcohol according to Bouveault- 

 Blanc. 



HO- CHjCHCHaCHjCHaCHCHaCHaCHaCHaCHCHaCHaCHaCHCHg- OH 



Colourless oil, b.p. i8o-i8i°/o.i mm (uncorr.). 



2:6:ii:i5-Tetramethylhexadecane-i:i6-diol is converted by the action of 

 hydrogen bromide into i: i6-dibromo-2:6: ii:i5-hexadecane, from which 

 perhydronorbixin can be obtained by condensation with sodium malonic ester, 

 saponification of the product and decarboxylation by heating to 200°^^'. 

 References p. 2^0-2^4. 



