THE LECITHINS 429 



Choline is extremely soluble in water. It also dissolves to a considerable 

 extent in method and ethyl alcohols and formaldehyde, but it is only slightly 

 soluble in amyl alcohol, acetone, and chloroform. It is practically insoluble 

 in such excellent fat solvents as dry diethyl ether, petroleum ether, benzene, 

 carbon disulfide, carbon tetrachloride, and toluene. ^'^''•^'^•' The presence of 

 small amounts of water in diethyl ether, or in ether-containing phospholip- 

 ids, will result in the solution of appreciable amounts of the base. 



The free base is quite susceptible to heat. It cannot be melted without 

 decomposition to trimethylamine^*^^ and glycol. ^''^ Wurtz^^^ found that a 

 dilute solution of choline was quite resistant to heat, whereas concentrated 

 solutions decomposed when heated to 190°C. Although losses occur during 

 evaporation to dryness, even of dilute solutions, it usually amounts to less 

 than 10% if 0.3 mg. is present, but may reach 100% if the final amount is 

 onlj^ 7 7.^*^* Less decomposition occurs when evaporation in vacuo is em- 

 ployed. On the other hand, choline chloride is much more stable to heat, as 

 no appreciable destruction occurs at 180°C.^'*^ Choline is stable when 

 boiled in barium hydroxide solution for 6 hours or in sodium ethylate for 24 

 hours. ^^^ 



Choline itself is a strong base which liberates ammonia from its salts and 

 precipitates the salts of heavy metals. The chloride, sulfate, nitrate, oxa- 

 late, acetate, carbonate, picrate, and picrolonate are readily soluble both in 

 water and in alcohol; on the other hand, the monophosphate, chloroplati- 

 nate, acid tartrate, and ruffianate dissolve in water but not in ethanol. 

 Certain other salts are practically insoluble in water, and this fact has re- 

 sulted in their usage in the quantitative determination of choline. Such 

 highly insoluble salts include the periodate {o\V-^° or crystalline material^''*), 

 the phospholungstate, the phosphomolybdate, and the reineckate (CsHh- 

 ON-C4H7N6S4Cr), as well as the double salts with gold chloride (chloroaur- 

 ate, CftHHON-Cl-AuCla) and with mercuric chloride (CgHnON-Cl- 

 6HgCl2). Insoluble salts are formed with Mayer's reagent (potassium mer- 

 curic iodide), as well as wdth Kraut's reagent (potassium bismuth iodide). 

 The ennea-iodide (C5H14ON • I • Ig) formed by treating choline chloride with 

 an excess of potassium triiodide is very insoluble in water, as is the hexaio- 



dide(C5Hi40N-I-l5)-i" 



A large number of qualitative methods for the detection of choline, as well 

 as quantitative procedures for its estimation, are based upon the production 

 of such insoluble compounds as those described above. Thus, the precipi- 

 tation of choline from an alcoholic solution as a double salt with platinum, 

 gold, or iron citrate is sensitive in dilutions of 1:2,000,000, although in 

 aqueous solutions platinum chloride is of no value. ^^"^ When aqueous solu- 



i«2 W. Gulewitch, Z. physiol. Chem., 24, 513-541 (1898). 



"3 W. Roman, Biochem. Z., 219, 218-231 (1930). 



16' G. Klein and 11. Linser, Biochem. Z., 250, 220-253 (1932). 



i« V. Stanck, Z. physiol. Chem., /,6, 280-285 (1905). 



i*« I. Sakakibara and T. Yoshinaga, J . Biochem. Japan, 23, 211-239 (1930). 



