164 PREPARATION OF METHYLATED SUGARS 



deposited in warty aggregates of microscopic prisms. These 

 showed the reverse mutarotation in acetone solution. 



Initial Specific Rotation. Permanent Specific Eotation. 



+81-9 > +48-3 



Dimethyl glucose is thus well adapted for the study of mutaro- 

 tation in that both stereoisomeric forms are available, and the 

 ready solubility of the sugar in solvents in which the change 

 is slow permits of the initial values being exactly determined. 

 The optical study of the compound is now complete, but the 

 results obtained are beyond the scope of this paper. 



DIMETHYL RHAMNOSE 



[Purdie and Young (Trans., 1906, 89, 1196).] 



The preparation of this compound resembled that just de- 

 scribed, but differed in one essential, in that only two hydroxyl 

 groups in rhamnose require to be protected from methylation. 

 This was effected by the use of Fischer's rhamnosemonoacetone. 

 The properties of dimethyl rhamnosemonoacetone, and of the 

 alkylated sugar obtained from it by hydrolysis, were normal, 

 but the detailed study of the substituted rhamnose was 

 restricted by the fact that it could not be obtained in the 

 crystalline state. It was however shown for the first time, 

 in the investigation to which reference is made above, that 

 the condensation of acetone with reducing sugars involves 

 two hydroxyl groups in the latter compounds. This result 

 is naturally of special importance in devising methods for 

 preparing partially methylated sugars. 



