CHAPTER VIII. (APPENDIX.) 

 PRACTICAL CHEMICAL METHODS AND DETAILS. 



A. GENERAL METHODS FOR THE SEPARATION AND ISOLATION OF 



BASES. 



WITH few exceptions the simple natural bases are readily soluble in 

 water, but not in ether or chloroform. As a rule they cannot therefore be 

 extracted from alkaline solution by shaking with organic solvents, and 

 the methods of Stas and DragendorfT, employed for the isolation of 

 vegetable alkaloids and based on the use of solvents immiscible with 

 water, are therefore not applicable. The earliest work on putrefaction 

 bases, therefore, suffered from too close adherence to the methods used 

 for alkaloids ; amylamine and phenyl-ethylamine which are readily 

 soluble in ether and in chloroform, and p-hydroxy-phenyl-ethylamine 

 which dissolves in amylalcohol, are among the few simpler bases which 

 can be isolated in this manner. 



In general, therefore, the isolation of these bases is effected by 

 means of an insoluble salt or other derivative, a method which in the 

 case of putrefaction bases was first extensively used by Brieger, with 

 conspicuous success. 



The simplest (aliphatic) monamines are volatile with steam and can 

 therefore easily be separated by steam distillation , first from acid solution 

 in order to remove non-basic volatile products and subsequently from 

 alkaline solution. Some non-volatile bases, particularly betaines, are 

 decomposed by strong alkalies with evolution of trimethylamine ; if 

 such bases are present the solution should only be made alkaline with 

 magnesium oxide and the distillation should be carried out at a low 

 temperature under reduced pressure. This precaution is for instance 

 important in the estimation of trimethylamine in urine. 



When bases have to be isolated from a complex mixture such as a 

 tissue extract, it is necessary to remove first proteins and peptones as 

 far as possible. The oldest method employed for this purpose is to 

 evaporate the aqueous extract to a small bulk and add alcohol which 

 precipitates the proteins, but leaves the salts of organic bases in solution. 

 The separation is, however, not very complete ; in some cases it may be 

 improved by using acetone instead of alcohol. The aqueous solution 



116 



