AND POLYHYDRIC ALCOHOLS 157 



the isolation of incompletely substituted derivatives other 

 than compounds of the nature of trimethyl glucose. In the 

 first paper of the series, however, the authors pointed out 

 that, in order to protect a sugar from oxidation during the 

 silver oxide reaction, all that is necessary is to substitute the 

 reducing group by a condensed residue capable of subsequent 

 removal by hydrolysis. For obvious reasons, derivatives of 

 the nature of methylglucoside have been largely made use of 

 for this purpose, but other types of sugar derivatives may also 

 be employed. Of these, the compounds produced by the 

 condensation of sugars with ketones or aldehydes are best 

 adapted for the purpose required. For example, a glucosidic 

 monoacetone derivative of a hexose must, irrespective of the 

 linkage of the acetone residue, contain three hydroxyl groups 

 capable of methylation, so that hydrolysis of the alkylated 

 product should give a trimethyl hexose ; similar treatment of 

 a diacetone derivative would result in a monomethylated 

 aldose or ketose. The remaining type of a partially alkylated 

 hexose would be represented by a dimethyl glucose, and this 

 has now been prepared by alkylation of monobenzylidene 

 methylglucoside, and removal of benzaldehyde and methyl 

 alcohol by hydrolysis. 



The principles sketched above have been found to be 

 capable of general application, and it is possible, by the 

 introduction of hydrolysable residues into the sugar molecule, 

 to protect selected hydroxyl groups from alkylation, so that 

 the preparation of a large number of partially methylated 

 sugars is 'thus rendered available. The process is also applic- 

 able to the preparation of similar derivatives from polyhydric 

 alcohols. 



The following table shows the methods adopted in the 

 formation of the more important compounds of this class 

 which have so far been obtained : 



