162 PREPARATION OF METHYLATED SUGARS 



It will afterwards be shown that the most probable 

 structure for the latter compound is that given below : 



CH 2 . CH . CH . CH(OH) . CH(OH) . CH(OCH) 3 



o o I o 



V 



A 



C 6 H H 



According to this view of the constitution a new asymmetric 

 carbon atom is introduced into the molecule, and thus benzal- 

 dehyde should condense with a-methylglucoside so as to pro- 

 duce two isomeric products. This possibility seems to have 

 been overlooked by Van Eckenstein, but we have succeeded 

 in isolating the hitherto unknown isomeride by cautious 

 crystallisation of the accumulated mother liquors obtained in 

 a large scale preparation of the condensation compound. 

 The new stereoisomeride crystallises in short prisms melting 

 at 148-149 and shows [ajjf+96'0 in aqueous solution. 

 This compound, which is only produced in small amount, is 

 therefore d-benzylidene-a-methyl-rf-glucoside. 



The methylation of Z-benzylidene-a-methylglucoside pro- 

 ceeded with unusual smoothness as, although acetone was 

 required to promote the solution of the compound in methyl 

 iodide, one treatment with the alkylating mixture was 

 sufficient to effect complete methylation. The product was 

 readily obtained in the crystalline state in nearly quantitative 

 amount, and, after recrystallisation from ligroin, melted at 

 122-123. The specific rotation in acetone solution for 

 c=l*64 was +97'03. It was found possible, by heating the 

 compound for one hour at 95 with one per cent, hydrochloric 

 acid, to remove the aromatic residue without affecting the 

 glucosidic group. The product of this reaction was therefore 

 dimethyl a-methylglucoside, which was isolated in the usual 

 manner. The compound, when crystallised from hot benzene, 



