276 CAROTENOID CARBOXYLIC ACIDS XIII 



CHj CH, CH, CH3 



HOCHjCHCHjCHjCHaCHCHaCHjCHaCHjCHCHjCHjCHjCHCHjOH 



CHg CH3 CH, CH5 



HOOCCHCHaCHaCHjCHCHaCHjCHjCHjCHCHaCHaCHjCHCOOH 

 Perhydrocrocetin 



Properties 

 Stable Crocetin C20H24O4: 



The pigment is obtained from acetic anhydride in brick-red rhombs, m.p. 

 285°. It is very sparingly soluble in the common organic solvents, but fairly 

 soluble in pyridine and in very dilute alkalis. Crocetin is fairly stable in air in 

 the solid state; the surface of the crystals is decolourised, however, under the 

 influence of light^^^. In alkaline solution on the other hand, the pigment ab- 

 sorbs oxygen from the air even at 20° ; this oxidation is considerably accelerated 

 by haemin^^*. With concentrated sulphuric acid, crocetin gives a deep blue 

 colour which soon changes into violet and eventually into brown*. No colour- 

 ation is observed with hydrochloric acid. 



For the separation of crocetin from other carotenoids, see the communi- 

 cation by KuHN and Brockmann^^^. A microchemical method of identification 

 is described by Tunmann^^^. 



Solvent Absorption maxima 



Carbon disulphide 482 453 426 mn 



Pyridine 464 436 411 m/z 



Chloroform 463 434,5 mfi 



Petrol 450.5 424.5 mn 



Hexane 445 420 400 m/i 



(cf. Fig. 22, p. 357) 



Disodium salt of crocetin C2oH2204Na2 : 

 Orange-5^ellow needles^^'. 



Dipotassium salt of crocetin C20H22O4K2 '■ 



This compound is obtained from aqueous ethanol in yellow crystals^^'. 



Diammonium salt of crocetin C2oH2204(NH4)2: 



Red needles from ammoniacal aqueous ethanol"'. 



Dipyridine salt of crocetin C20H24O4.2C5H5N : 

 Dark red plates from aqueous pyridine^i®. 



Crocin was first obtained in the crystalline state by Karrer and Salomon^^^. 

 It was recognised as the digentiobiose ester of crocetin by Karrer and Miki^^o^ 



* Further colour reactions are described by P. Karrer and co-workers, Helv. chim. 

 Acta II (1928) 1201. 

 References p. 2^0-294. 



