212 



of solubility is often sufficiently great to allow a practically complete 

 fission of A A' by simply combining it with /. 



If, however, the difference of the solubilities between Af and A'f 

 is not great enough, a useful modification of the method described 

 was proposed by Pope and Peachy 1 ). If only so little of / be 

 present, as to give precisely the theoretical quantity of the less 

 soluble compound^!/, while the other component A ' of the racemoid 

 be bound to some optically wactive substance p, giving with it a very 

 soluble compound A'p, then, if the solution is allowed to crystal- 

 lise slowly, a certain amount of Af will every moment be with- 

 drawn from the equilibrium-mixture in the remaining solution. 

 As a consequence, this equilibrium will be displaced so that a new 

 quantity of Af is produced, which again will be deposited; etc. 



The result is that Af is completely gained in the crystalline state, 

 while A'p remains in the mother-liquid, from which A' can easily 

 be isolated afterwards. Pope and Peachy have used this method 

 e. g. to separate the racemic tetrahydro-quinaldine into its optically 

 active components, by means of the action of ammonium-bromo-cam- 

 phor-sulponate (1 mol.) on inactive tetrahydro-quinaldine-hydrochlo- 

 ride (2 mol.); etc. 



If the combinations Af and A'f are sufficiently loose, it will after- 

 wards be possible to set A and A' free by fixing / and /' to another 

 substance 5 to which they have greater affinity. In such a way 

 racemic bases may be separated by means of an optically active 

 acid, or racemic acids by means of an optically active base. This 

 method is however not restricted to these two classes of compounds. 



In later times Erlenmeyer 2 ) and Neuberg 3 ) have extended 

 the method to condensation-processes with optically active aldehydes, 

 nitrogen-compounds (hydr W-derivatives) ; etc. We will again 

 return to those investigations afterwards. 



8. Pasteur's first fission of a racemoid according to the 

 method described, was the fission of the racemic acid itself into 

 the tartaric acids by the aid of the dextrogyratory base cinchonine 4 ) 

 Later he did this by means of quinicine and cinchonicine, which 

 bases are both dextrogyrate also. From the solution, the cinchonicine- 



1) W. J. Pope and S. J. Peachy, Journ. Chem. Soc. London 75. 1066. (1899). 



2) E. Erlenmeyer Jr., Ber. d. d. Chem. Ges. 36. 976. (1903). 



3) C. Neuberg, Ber. d. d. Chem. Ges. 36. 1192. (1903). 



4) L. Pasteur, Compt. rend. 36. 191. (1852); Ann. de Chim. et Phys. (3). 

 38. 437. (1853). 



