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the replacement of a hydrogen, metal, or halogen atom by a methyl group,—CHs; it is effected by the action of various methylating agents—for example, methyl iodide, CH3I; dimethyl sulfate, (CH3O)2SO2; methylsulfuric acid, CH3OSO3H; methyl esters of organic sulfo acids; methanol, CHjOH; and dimethyl ether, (CH3)2O. Methylation is widely used in organic synthesis in industry. For example, methylation with dimethyl sulfate is used in the synthesis of pharmaceuticals (for example, metapyrin); amidopyrine is prepared by methylation with formaldehyde and a reducing agent, usually formic acid.
Aromatic hydrocarbons are readily methylated by the action of methyl chloride or dimethyl ether in the presence of AlCl3. Methylaniline and dimethylaniline are prepared industrially by methylation of aniline with methanol over A12O3 at high temperatures:
Methylation with diazomethane is widely used to produce methyl esters of carboxylic acids under laboratory conditions, according to the formula
R—COOH + CH2N2→RCOOCH3 + N2
B. L. DIATKIN