233 



lose their rotatory power rather rapidly, in aqueous solution much 

 faster than in a mixture of acetone and water. 



In the case of this chromium-salt, Werner during its fission 

 observed another phenomenon, which may be briefly mentioned here. 

 With the exception of a very small portion, the inactive substance 

 appeared to be completely activated by the usual method into one 

 of the antipodes; but, if the potassium-strychnine-S3.lt, used in these 

 experiments for the purpose of separation into the optically-active 

 components, was recrystallised from water, the antipode obtained 

 turned out to be laevogyr&tory , while the same experiments carried 

 out in alcoholic solutions, gave the ^^rogyratory component. 



The explanation of this strange phenomenon, as given by Werner, 

 is, that the active salts come into existence only during the process 

 of crystallisation itself, while the solutions evidently have a strong 

 tendency to get rapidly inactive by autoracemisation. In water the 

 laevogyratory component is less soluble than the other one; but 

 it is just the dextrogyratory salt that crystallises first from alcohol. 

 If the alcoholic, racemic solutions, therefore, be concentrated on 

 the waterbath, the less soluble active salt is deposited, and the 

 equilibrium of the remaining optically active mother-liquor is now 

 rapidly restored by autoracemisation, so that a new quantity of 

 the one antipode is formed again, which is precipitated now by 

 sufficient addition of alcohol, since it is the less soluble component. 

 In this way the whole amount of salt can, by the occurring and 

 successive displacements of the equilibrium, and by the removal 

 of the less soluble antipode 1 ), be finally completely converted into 

 one of the two optically active components. 



Undoubtedly the mechanism of such autoracemisation includes an 

 intermediate stage of temporarily detaching of the groups from the 

 central metal-atom. The already mentioned triethylenediamine- 

 cobalti-, and the corresponding rhodium-salts can, however, be boile'd 

 in solution without the rotatory power of it perceptably diminishing. 



On closer examination it is found that the phenomenon described 

 is really connected with the reaching of a state of equilibrium between 

 the two enantiomorphously related molecules in the solution, equili- 

 brium being arrived at if the molecules of both components be 

 present in equal number. 



A. Werner, Ber. d. d. Chem. Ges., 45, 3064, (1912). 



