Question

Question: Propose a mechanism for methylation of any one of the hydroxy groups of $\mathbf{methyl}\mathbf{-}\mathbf{\alpha }\mathbf{-}\mathbf{D}\mathbf{-}\mathbf{glucopyranoside}$,using and dimethyl sulfate.

Short answer

The most common method for forming simple ethers is the Williamson ether synthesis that involves a strongly basic alkoxide ion. A sugar is believed to be iosmerized and decomposed under these basic conditons.

Step-by-step solution

Step-by-Step solutionStep 1: Ether formation

The most common method for forming simple ethers is the Williamson ether synthesis that involves a strongly basic alkoxide ion. A sugar is believed to be iosmerized and decomposed under these basic conditons.

Mechanism

From modified Williamson method, it is known that a sugar can be first converted to a glycoside by the treatment with an alcohol and an acid catalyst. Since glycoside is an acetal, therefore it is stable to base. Further treatment of glycoside with sodium hydroxide and dimethyl sulfate yields the methylated carbohydrate.

Mechanism for methylation of any one of the hydroxy groups