AND POLYHYDRIC ALCOHOLS 169 



alcohol and n-propyl alcohol as the essential fermentation 

 products. 



As the more fully alkylated sugars are not fermentable, 

 work of this nature could not be extended beyond the limits 

 specified. 



PARTIAL ALKYLATION OF POLYHYDRIC ALCOHOLS 



Generally speaking, the same principles are utilised in the 

 preparation of partially methylated polyhydric alcohols as 

 apply to the formation of the corresponding substituted sugars, 

 i.e. the methylation of a derivative which still contains 

 hydroxyl groups, and the removal of the substituting residue 

 by hydrolysis. 



In the case of the alcohols most closely related to the sugars, 

 suitable derivatives for this purpose are practically unknown, 

 in fact the mechanism of the formation of condensation pro- 

 ducts is probably dissimilar in the two classes referred to, in 

 virtue of the presence of an acidic reducing group in the sugars 

 and the absence of such a group in the alcohols. It will be 

 seen that, in the case of alcohols where an even number of 

 hydroxyl groups are available for condensation with a ketone, 

 a completely substituted derivative will in most cases result. 

 It is only when the alcohol under examination contains an odd 

 number of hydroxyl groups that the methylating reaction may 

 be directly applied to the acetone derivative. Thus, arabitol 

 can only condense with two molecules of acetone as a 

 maximum, and consequently one hydroxyl group is thus left 

 available for methylation. On the other hand, in the case 

 of mannitol, condensation with acetone gives a triacetone 

 derivative which is naturally unaffected by alkylation, and, 

 moreover, it is impossible to control the condensation so as to 

 stop the reaction when only one or two acetone residues have 

 entered the molecule. 



This difficulty may be overcome by taking advantage of 

 the fact that the acetone residues in mannitol triacetone may 



