| http://www.w3.org/ns/prov#value | - Pursuant to this invention, the methylation with methyl bromide or methyl chloride is performed in a halogen-free liquid solvent comprising at least 40% by weight (preferably in the range of about 40 to about 70% by weight) of one or more compounds of the formula RZ where R is a hydrogen atom or an alkyl group, and Z is a hydroxyl group or a cyanide group (with the proviso that if Z is a cyanide g
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