Action of Dimethyl Sulphate on Magnesium Alkyl or Aryl Halide Grignard

Reaction IX. (c) Action of Dimethyl Sulphate on Magnesium Alkyl or Aryl Halide (Grignard).—When a Grignard compound is treated with dimethyl sulphate, methylation of the alkyl or aryl group takes place, the metal-halogen residue being split off. (B., 36,2116. See also O.S., XI., 66.) 

The yields are good, as is to be expected from the components of the reaction. 

It will be noted that in the Grignard reactions so far described, only bromo- or iodo-compounds are mentioned. Chlorine compounds do not enter so readily into this reaction to induce them to react it is usually necessary to add a crystal of iodine (B., 38, 2759), or mercuric chloride (C., 1907, I., 872), or a previously prepared magnesium solution (B., 38, 1746 C., 1907, I., 455), or a small amount of Gilman s catalyst (Rec., 1928, 47, 19), which is prepared by heating an alloy of Mg containing 12-75% of Cu with about 20% iodine in vacuo. 

By the method above outlined, toluene has been prepared from bromo-benzene, and p-xylene from p-bromotoluene. 

Owing to the closeness of the boiling points of the three xylenes they cannot be readily separated one from the others so that a method such as the above, by which one isomer can be obtained free from the others, in a good yield, is of importance. For some details on magnesium aryl halides, see B., 36, 2898, and O.S., X., 4. 

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