2 CROCETIN 277 



The sugar residues of crocin are very readily split off by alkalis. On working 

 in aqueous media, crocetin is obtained, whereas in the presence of methanol, 

 methyl esters of the pigment are formed^^^. 



Crocin C44H64O24 : 



CH3 CH3 CH3 CH3 



-HCOO(>-C=CH-CH=CH-C=CH-CH=CH-CH=C^CH=CH-CH=C-COOCH 1 



r 



(CH0H)3 (CH0H)3 



I CH CH 1 



I I 1 1 ^ 1 i 



CHgO • CH(CH0H)3CH • CHjOH H0CH2CH(CH0H)3CH • OCHj 



Crocin dissolves readily in water to give an orange-red solution. M.p. 186° 

 (with frothing). Crystals of crocin contain water of crystallisation which is only 

 given up on prolonged drying in vacuum at 100°. 



Stable crocetin niononiethyl ester (/3-crocetin) C21H26O4: 



This mono-ester is obtained either by the replacement esteiification of crocin 

 with 70 % methanol and potassium hydroxide, or by the esterification of cro- 

 cetin with dimethyl sulphate^^^. The ester crystallises from chloroform in 

 rectangular leaflets, m.p. 218°. 



Stable crocetin dimethyl ester (y-crocetin) C22H28O4: 



This ester is best prepared by the replacement esterification of crocin^^^, 

 but it can also be obtained by the esterification of crocetin with diazomethane^^^. 

 Hexagonal leaflets, m.p. 222.5° (corr.)^24_ (With regard to the isomerisation of 

 labile crocetin dimethyl ester, see p. 273). Crocetin dimethyl ester can be 

 distilled unchanged in vacuum. The dry-distillation is described by Kuhn and 



WlNTERSTEIN^^^. 



Solvent Absorption maxinia^^^ 



Petrol 450.5 424.5 m// 



Chloroform 463 434.5 m// 



(of. Fig. 18, p. 355) 



At 20°, one part of crocetin dimethyl ester dissolves in 100,000 parts of 

 methanol. The solubility in ether is also very small. 



Labile crocetin dimethyl ester C22H28O4 : 



According to Kuhn and Winterstein^^', labile crocetin occurs esterified 

 with gentiobiose in the blossoms of saffron {Crocus sativus). It has only been 

 isolated in the form of its dimethyl ester. 



The labile dimethyl ester is formed together with the stable form by the 

 action of dilute sodium hydroxide on a methanoHc extract of saffron. The 

 References p. 2go-2g4. 



