PURDIE'S REACTION 181 



present time, the reaction has been almost exclusively em- 

 ployed in the preparation of derivatives of active compounds, 

 and in no case has an optical change of the nature of the 

 Walden inversion been noticed. Purdie and Barbour (9) 

 definitely proved that no inversion of this kind occurred on 

 methylating methyl d-tartrate, as on hydrolising the methyl di- 

 methoxysuccinate produced they obtained a dimethoxysuccinic 

 acid, which, when reduced with hydriodic acid, gave d-tartaric 

 acid. The proof has been extended by Irvine (33) to the 

 methyl Z-methoxy-propionate obtained by the methylation 

 of methyl Z-lactate. The substance was reduced with hydri- 

 odic acid and yielded Wactic acid, which was identified by 

 conversion into its zinc salt. The silver oxide method of 

 alkylation has therefore no disturbing effect on the configura- 

 tion of an active lactate. In some few cases (McKenzie (3) ) 

 racemisation has been observed, but it is not certain whether 

 this occurred during the actual reaction or in the isolation of 

 the product. 



A modification of the reaction has been devised by Forster 

 (44 and 45) for the purpose of esterifying acids without risk of 

 racemisation. Silver oxide, in slight excess of the calculated 

 amount, was mixed with an ethereal solution of Z-a-triazo- 

 propionic acid, and, without separating the silver salt from 

 the unchanged oxide, excess of ethyl iodide was added and 

 left in contact with the mixture for thirty-six hours. The 

 filtered solution yielded the desired ethyl Z-a-triazopropionate 

 CHg.CHNs.COgCgHg. Ethyl Z-a-triazobutyrate was prepared 

 in a similar manner. 



By the action of silver oxide and methyl iodide on salicylic 

 acid, Lander (4) obtained pure methyl o-methoxybenzoate. 

 Similarly McKenzie (3) prepared i-ethyl phenylethoxy acetate 

 from t-mandelic acid, and Denham converted glyceric acid 

 into methyl a/3-dimethoxypropionate (private communica- 

 tion). We have here instances of esterification of the acids 

 and alkylation of alcoholic hydroxyl groups proceeding 



