ISOLATION, CHEMICAL CONSTITUTION AND SYNTHESIS 



2. ISOLATION, CHEMICAL CONSTITUTION AND 

 SYNTHESIS OF CHOLINE 



Isolation 



Choline was discovered in 1862 by A. Strecker/ who isolated it 

 from the bile of cattle and pigs. It has also been isolated from a 

 large variety of fungi and flowering plants, especially from the seeds 

 of the latter. In animals, it is a constituent of phospholipids, e.g. 

 brain and egg-yolk lecithin and sphingomyelin, and of acetylcholine, 

 the mediator of nerve impulse transmission. 



Choline was isolated from egg-yolk by the following method.^ 

 The yolks were extracted with ether, and the insoluble residue was 

 extracted with hot alcohol. The combined extracts were evaporated 

 to dryness and the residue was heated with methanolic barium hy- 

 droxide solution. After removal of the excess baryta with carbon 

 dioxide the filtrate was evaporated and the residue taken up in water 

 and filtered. The filtrate was again evaporated and the residue 

 taken up in alcohol, filtered and the filtrate treated with mercuric 

 chloride solution. The precipitate that formed was filtered off and 

 dissolved in hot water, and hydrogen sulphide was passed into the 

 solution. The mercury sulphide precipitate was filtered off and the 

 filtrate evaporated. Dilute hydrochloric acid was added to the 

 residue, and the solution was again evaporated. The residue was 

 talcen up in alcohol, the solution diluted with water and the choline 

 precipitated with alcoholic cadmium chloride solution. 



Constitution and Synthesis 



Choline was shown to be /3-hydroxyethyl-trim ethyl-ammonium 

 hydroxide : 



(CH3)3N . CH2 . CH2OH 



OH 



by A. Baeyer ^ and A. Wurtz.^ It was first synthesised by the action 

 of trimethylamine on j8-chloroethyl alcohol or ethylene oxide, ^ but it 

 has also been prepared by heating ^-bromoethyl-trimethyl-ammonium 

 bromide in aqueous solution at 160° C. ^ or in alcoholic potassium 

 hydroxide solution at 120° C.^ It is more conveniently made, how- 

 ever, by hydrolysis of lecithin with acid "^ or alkali.® 



References to Section 2 



1. A. Strecker, Annalen, 1862, 123, 353. 



2. F. W. Schmidt, Z. physiol. Chem., 1907, 53, 428. 



3. A. Baeyer, Annalen, 1866, 140, 306 ; 1867, 142, 322. 



4. A. Wurtz, ibid., 1868, Suppl. 6, 116, 197. 



585 



