38 



ORIGIN AND MAINTEN. OF OPT. ACTIVITY 



siclerably modified our ideas concerning the maintenance 

 of the asymmetric state. 



Among the first observations on this subject, one should 

 mention those of Bredig and Fajans (1908) and those of 

 Fajans (1910) on the asymmetric splitting of racemic 

 camphorocarbonic acid into camphor and carbonic acid in 

 the presence of various catalysts. 



Almost simultaneously, Rosenthaler (1908) began his 

 studies on the asymmetric synthesis of the nitrite of man- 

 delic acid, which were later on repeated and extended by 

 a number of other investigators and which constitute, at 

 present, the basis for the general theory of asymmetric 

 synthesis. He observed that, by combining the symmet- 

 ric molecule of benzaldehyde with the symmetric molecule 

 of hydrocyanic acid under the action of the asymmetric 

 catalyst emulsine, one obtains an optically active nit rile 

 of mandelic acid. A considerable excess of dextrorotatory 

 over laevorotatory nitrite was recorded. Rosenthaler 

 also pointed out that the optical activity of the product 

 synthesized by emulsine reached a maximum value after 

 a certain time and then decreased (r/. Table 7 ). 



TABLE 7 



Change in Optical Activity during the Enzymatic Synthesis of the 



NiTRiLE OF Mandelic Acid (Eosenthaler, 1908) 



(The numbers give the optical rotation of the synthetic product) 



Other observations on the change of optical activity dur- 

 ing asymmetric synthesis were made by Nordefeldt 

 (1922). The optical activity was found to tend asympto- 

 tically to zero {cf. Fig. 3). 



Bayliss (1913), Krieble (1913) and Nordefeldt (1922) 

 showed the important fact that the synthesis of racemic 

 mandelo-nitrile takes place in the absence of enzymes and 



