THE LECITHINS 411 



(3) Pi'eparation of the Lecithins 



Practicall}^ all of the methods for the preparation of lecithin employ its 

 precipitation from alcoholic solution as the cadmium salt. The chief 

 procedures are those of INIacLean^ and of Levene and Rolf^^-*^ for the 

 separation of lecithin from egg-yolk, and of Levene and Rolf^^ for the 

 preparation of this phospholipid from such organs as brain and liver. 



MacLean extracts the lecithin from the diced and pulverized egg-yolk 

 \\ath alcohol; then the extract is treated with alcoholic cadmium chloride 

 solution to precipitate the lecithin. The precipitate is washed with alcohol 

 and is stirred up with about 15 volumes of ether containing a trace of al- 

 cohol. The cadmium salt is separated by centrifugation, washed with 

 ether, dried, and decomposed with alcoholic ammonium carbonate; the 

 alcoholic solution of lecithin is then filtered hot. Further treatment con- 

 sists in the concentration of the alcohol, the residue being taken up with 

 ether, and in the precipitation of the lecithin with an excess of acetone. 

 It can be further purified through emulsification with water and precipita- 

 tion with acetone. This precipitate is dissolved in alcohol and is again 

 precipitated as the double salt by cadmium chloride, and this is again 

 recrystallized from a mixture of 2 parts of ethyl acetate and 1 part of 80% 

 alcohol. The cadmium salt is again decomposed with ammonium car- 

 bonate and the lecithin is reprecipitated from aqueous solution by acetone. 

 By the use of this procedure, JMacLean obtained a preparation of lecithin 

 with a N:P ratio of 1:1 which contained choline as the sole nitrogenous 

 component. 



For the preparation of lecithin from egg-3'olk, Levene and Rolf''^ treat 

 the sample first with acetone, to remove some of the other phosphatides 

 which are otherwise separated with diffi.culty from lecithin. The acetone 

 suspension is allowed to stand for at least 24 hours at 0° C, and the different 

 crystalline residues are filtered off without letting the temperature exceed 

 10°C. This undissolved mass consists largely of fat and lecithin -wnth a 

 small amount of cephalin. The residue is taken up in 2 volumes of alcohol, 

 and is allowed to stand for some time at 0°C. The fats remain undissolved, 

 and are separated by filtration. After concentration of the alcoholic 

 filtrate to about one-half the ^'olume, under reduced pressure, lecithin is 

 precipitated as the cadmium salt, with alcoholic cadmium chloride. The 

 pulverized precipitate of the cadmium salt is dissolved in toluene, in which 

 it forms a clear solution on warming, especially if the solvent contains 

 a small amount of water. Any cerebrosides present cause an opalescence. 

 They may be removed by centrifugation. Four volumes of cold ether 

 containing 1% water are added, the lecithin is slowly precipitated, and the 

 precipitate is removed by centrifugation. It is then washed with ether, 



« P. A. Levene and I. P. Rolf, /. Biol. Chem., 46, 193-207 (1921). 

 « P. A. Levene and I. P. Rolf, ./. Biol. Chem., 72, 587-590 (1927). 



