PURDIE'S REACTION 187 



product was sufficient for the purpose. Considering the 

 superior activity of the alkyloxy-acids as compared with the 

 corresponding hydroxy-acids, it will be seen how suitable 

 the former are for work of this kind. 



McKenzie's racemic methoxyphenylacetic acid has been 

 used by Marckwald and Paul (37) in demonstrating Marck- 

 wald's general method for effecting asymmetric synthesis. By 

 heating a racemic acid with an optically active base to a suffi- 

 ciently high temperature it is theoretically possible, by reason 

 of the inversion which active acids frequently undergo at high 

 temperatures, to obtain a salt-mixture containing the d- and 

 Z-acids in unequal quantities. Thus inactive methoxyphenyl- 

 acetic acid was heated with strychnine for eighteen hours at 

 150-160 C.,and from the mixture an acid was isolated, having 

 a specific rotation of O32. 



McKenzie has himself utilised <ZZ-phenylethoxy acetic, 

 cZZ-ethoxypropionic and other acids in the course of important 

 work which resulted in similar asymmetric synthesis 

 (M c Kenzie and Thompson (29) ). If one of these racemic 

 acids be partially esterified with Z-menthol, the acid 

 remaining unesterified is laevorotatory ; the ester so 

 formed, when hydrolysed with potassium hydroxide, yields 

 an acid which contains an excess of the Z-form. These 

 phenomena are due to the fact that the rate of formation of 

 the ester Z-base-eZ-acid is greater than that of the Z-base- 

 Z-acid ester ; the residual acid hence contains an excess of the 

 Z-isomeride. The Z-base-cZ-acid ester which constitutes the 

 larger portion of the ester formed, since it is formed more 

 readily than the Z-base-Z-acid compound, is also hydrolysed 

 more rapidly than the latter. During the earlier part of the 

 hydrolysis, therefore, the d-acid is liberated in greater quantity 

 than the Z-acid, and in contact with the unused potassium 

 hydroxide undergoes partial or complete racemisation. The 

 remaining ester is now largely the Z-base-Z-acid form, and 

 being hydrolysed by the reduced quantity of potassium 



