CHAPTER XII 



Carotenoids of known or largely known structure 

 containing one or more carbonyl groups 



I. /3-CITRAURIN C30H40O2 



History and Occurrence 



In the course of investigations of carotenoids from orange peel {Citrus 

 aurantium), Zechmeister and Tuzson^ discovered a previously unknown 

 pigment for which they proposed the term citraurin*. Citraurin occurs in 

 oranges together with carotene, cryptoxanthin, zeaxanthin, xanthophyll and 

 violaxanthin. It has not, so far, been isolated from any other source. 



Preparation^ 



Orange peels are dehydrated with ethanol and extracted with peroxide-free 

 ether. After removal of the solvent in a partial vacuum, a red oily residue remains. 

 In order to separate the pigments from the oily constituents, this residue is dissolved 

 in petrol and chromatographed on calcium carbonate. The oily components, 

 together with carotene and cryptoxanthin, are removed by prolonged washing. The 

 violet-red zone which contains ^-citraurin is eluted with a mixture of ether and 

 methanol, and the pigment esters are saponified with methanolic potassium 

 hydroxide. After saponification is complete, the free phytoxanthins are dissolved 

 in ether, the solution is evaporated to dryness and the residue is dissolved in warm 

 carbon disulphide. On cooling this solution, much pigment material crystallises 

 (violaxanthin etc.) while ^-citraurin remains in solution. It is adsorbed on a calcium 

 carbonate column which is washed with carbon disulphide. ^-Citraurin forms a red 

 zone in the chromatogram and is eluted with a mixture of ether and methanol. 

 After removal of the solvent, the residue is dissolved in a little hot methanol, from 

 which |8-citraurin crystallises in round, reddish aggregates on addition of a little 

 water. 35 mg of pigment were obtained from 100 kg of oranges. 



P. Karrer and co-workers, Helv. chim. Acta 20 (1937) 682, 1020 proposed the term 

 )5-citraurin for the pigment discovered by L. ZecHxMeister and P. TuzsoN^ in order to 

 avoid confusion with the isomeric a-citraurin (cf. p. 205). 



References p. 2^3—25$. 



