CHAPTER XIII 



Carotenoid carboxylic acids 



I. BIXIN C25H30O4 



History 



1825 BoussiNGAULT^ is the first to describe bixin, the pigment of Orleans, 



which has since been investigated by numerous workers^. 

 1878 Etti^ succeeds in crystalhsing bixin. 

 1917 Heiduschka and Panzer^ carry out careful elementary analyses of bixin 



and are the first to assign the correct empirical formula to the pigment. 

 1928-33 KuHN and co-workers^ propose a structural formula for bixin which 



is confirmed by Karrer and co-workers by the total synthesis of per- 



hydronorbixin^. 



Occurrence 



Bixin has only been found in Bixa orellana. The fresh seeds of this plant are 

 surrounded by an orange-red mass which contains most of the pigment. After 

 drying, the seeds are surrounded by a brown-red crust. Bixin also occurs in 

 other organs of the plant, e.g. the secretionary cells of the leaves, and appears 

 in the form of numerous brown spots on the lower side of the leaf. 



Preparation"^ 



a) From commercial Orleans. The commercial preparation is finely ground and 

 allowed to stand for several days covered with acetone. The material purified in 

 this way is dried in air and the pigment is extracted with chloroform in a Soxhlet 

 apparatus. It is crystallised from the same solvent, or from ethvl acetate or acetic 

 acid. By this method good preparations of the labile bixin are obtained but the 

 yield is decreased by the pre-extraction with acetone. 



b) From "pate de rocou". The red dough is stirred up with methanol and the 

 bixin is converted into its ammonium salt by addition of ammonia. The salt is 

 extracted with water and the solution is filtered. The filtrate is acidified with acetic 

 acid, when bixin is precipitated as a red powder. It is filtered, washed with methanol 

 and extracted with chloroform. The crude preparation is then recrystallised. In 

 this way about 500 g of bixin are obtained from 25 kg of "pate de rocou". 

 References p. 290-294. 



