THE T.T^OITTITNS 413 



alcohol fractions are combined and are used for the determination of the 

 lecithin isomers. 



The alcohol is evaporated from the lecithin fractions, after which the 

 residue is dissolved in a small amount of ether. This is allowed to stand 

 overnight in the refrigerator for the precipitation of spliingomyelin. After 

 removal of the sphingomyelin, the lecithin is pi'ecipitated as the cadmivmi 

 salt by the addition of a cold saturated solution of cadmium chloride in 

 absolute alcohol until no more precipitation occurs. After centrifugation, 

 the precipitate is further washed twice with 5-ml. portions of a 7: 3 alcohol- 

 ether mixture. 



In order to separate the a- and ;S-lecithins, acetone is added and is 

 thoi'oughly mixed with the precipitate by means of a stirring rod. The 

 tube is placed in a hot-water bath which is gently heated to boiling for 2 

 minutes. The cadmium salt of /3-lecithin dissolves in the acetone, while 

 the salt of the a-lecithin is insoluble. After the residue is washed twice 

 with acetone, the |8-lecithin is determined on the combined acetone wash- 

 ings, while the a-lecithin is estimated on the residue. Welch^^ employed 

 the Bloor oxidation method^^ for the determination of the lecithin in each 

 of these fractions. 



(5) Synthesis of the Lecithins 



The first attempts to synthesize lecithin were made by Hundeshagen^^ 

 as early as 1883 and by Gilson^^ 5 years later. These workers did not 

 obtain well-defined products which gave the expected hydrolysis products. 

 Although Griin and Kade^^ succeeded in preparing the glycolchlorohydrin 

 ester of distearylglycerol phosphoric acid, they failed to obtain sufficient 

 amounts of lecithin on treatment of this compound with trimethylamine 

 to render its identification certain. 



a. a-Lecithin. The first satisfactory synthesis of a-lecithin was made 

 by Griin and Limpacher.^^'^^ These workers used Q:,/3-distearin as a 

 starting material. This was condensed with phosphoric acid anhydride, 

 whereby the Q!,j8-distearin metaphosphoric acid ester was formed. When 

 this ester was treated with 2 equivalents of choline bicarbonate, the choline 

 salt was obtained from which lecithin was synthesized in a 60-70% yield. 

 It is necessary to use the bicarbonate to counteract the strongly basic 

 hydroxyl in the nitrogen. If this is not done, the group will react with the 

 phosphoric acid residue, resulting in the formation of a salt rather than of 

 an ester. This series of reactions is illustrated here: 



M W. R. Bloor, J. Biol. Chem., 82, 273-286 (1929). 

 89 A. Grun and F. Kade, Ber., 45, 3367-3376 (1912). 

 «» A. Griin and R. Limpacher, Ber., 69, 1350-1360 (1926). 

 " A. Griin and R. Limpacher, Ber., 60, 147-150 (1927). 



