PURDIE'S REACTION 197 



supply an explanation of this apparent anomaly, and afford 

 an insight into the mechanism of this particular case of 

 alkylation. Such methylation might be supposed to proceed 

 either by the intermediate formation of an additive compound 

 of sugar and alkyl iodide and subsequent removal of hydrogen 

 iodide, or by the intermediate formation of a silver derivative 

 in which silver replaces the glucosidic hydrogen atom. In 

 the latter alternative, if the /3-sugar formed a silver derivative 

 in this way and methyl iodide reacted with the resultant 

 substance, the presence of a large excess of the /3-glucoside 

 in the product would be accounted for. This supposition is 

 rendered unlikely, however, by the failure, after repeated 

 attempts, to obtain any evidence of the formation of a silver 

 derivative of tetramethyl glucose. On the other hand, 

 solutions of tetramethyl glucose in alkyl halides showed 

 remarkable abnormalities in optical activity at low tempera- 

 tures, and these abnormalities (the details of which cannot be 

 given here) can be explained by association between the sugar 

 and the alkyl iodide. It appears probable, therefore, in view 

 of the existing evidence of the occasional quadrivalency of 

 the oxygen atom, that in this case alkylation occurs by 

 intermediate formation of a methyl iodide additive compound 

 from which hydrogen iodide is subsequently removed by the 

 agency of silver oxide. The change may be represented 

 schematically as follows : 



C C 



C C C C 



,OH | I ,OH ' \/ \OCH 3 



Y 



y/ \ 



\ C C 



/\ I X I I /OCH 3 



CH 3 I CH 3 C G/ 



X/ \H 

 



