28o CAROTENOID CARBOXYLIC ACIDS XIII 



Dihydrocrocetin dimethyl ester C22H30O4 : 



This ester was obtained by Karrer and Helfenstein^^' by the action of 

 diazomethane on dihydrocrocetin and by Kuhn and Winterstein by hydro- 

 genation of stable^^^ or labile^^^ crocetin dimethyl ester in pyridine with zinc 

 dust and acetic acid. 



This compound separates from ether in sulphur-yellow crystals, m.p. 96°. 

 On shaking a solution in piperidine with air, stable crocetin dimethyl ester is 

 rapidly formed^^^. If the pigment is dissolved in pyridine and little sodium 

 hydroxide is added, a deep blue colomration is immediately produced. This 

 rapidly changes to orange-red on contact with air, due to the oxidation of the 

 dihydroderivative to the stable crocetin dimethyl ester^*". 



Dihydrocrocetin diethyl ester C2,;H3404 : 



This ester is prepared by treating dihydrocrocetin with diazoethane^*^. 

 M.p. 62°. Dihydrocrocetin diethyl ester is very readily soluble in organic 

 solvents. 



Hexahydrocrocetin C00H30O4 : 



Hexahydrocrocetin was prepared by Karrer and co-workers^*^ by the 

 reduction of crocetin wdth excess titanium trichloride. It is a light yellow oil 

 which is very stable towards atmospheric oxygen. On catalytic hydrogenation 

 it is converted into perhydrocrocetin. On addition of concentrated sulphuric 

 acid a brown-red colouration is produced. 



6:ii-Dimethylhexadi>cane-2:i ^-dicavboxylic acid, perhydrocrocetin C20H38O4 : 



The total synthesis of this compound has already been described (p. 275). 

 It is also formed by the catalytic hydrogenation of crocetin^*^. Perhydro- 

 crocetin has also been prepared from i : i6-dihydroxy-2 : 6 : 11 : 15-tetramethyl- 

 hexadecane-i : i6-dicarboxylic acid dimethyl ester (cf. p. 266)^**. The ester was 

 treated with methyl magnesium iodide, the tetrahydroxyderivative formed was 

 reacted with lead tetraacetate, and the resulting dialdehyde was oxidised with 

 chromic acid and acetic acid. 



Perhydrocrocetin dianiide C20H40O2N2: 



Perhydrocrocetin is converted into the acid chloride by means of thionyl 

 chloride and the acid chloride is reacted with concentrated aqueous am- 

 moniai*^' i^^. M.p. 130°. 



a:a'-Dihydroxyperhydrocrocetin dimethyl ester C22H420g (I) : 



CH3 CHo CHo CHo 



II II 



HjCOOC- C-CH2CH2CH2CHCH2CH2CH2CH2CHCH2CH aCHaC- COOCH3 



OH OH 



I 



References p. 2go-2g4. 



