Q.Give three methods of preparation of anisole.

Anisole (methyl phenyl ether) is most commonly made by alkylating a phenoxide with a methylating agent — methyl iodide (Williamson synthesis), dimethyl sulphate, or diazomethane all serve this purpose.

Method 1 — Williamson's ether synthesis (most standard method): Sodium phenoxide (from phenol + NaOH) is refluxed with methyl iodide (or another methyl halide); the phenoxide oxygen (nucleophile) displaces iodide in an $S_N2$ reaction:

$C_6H_5OH \xrightarrow{NaOH} C_6H_5ONa \xrightarrow{CH_3I} C_6H_5-O-CH_3\ (\text{Anisole}) + NaI$

Method 2 — Using dimethyl sulphate: Phenol is treated with dimethyl sulphate, $(CH_3)_2SO_4$, in the presence of aqueous/dilute NaOH (which generates the phenoxide in situ and also serves as base to take up the acid byproduct):

$C_6H_5OH + (CH_3)_2SO_4 \xrightarrow{NaOH} C_6H_5OCH_3\ (\text{Anisole}) + CH_3OSO_3Na$

This is a commercially convenient methylating method since dimethyl sulphate is a cheap, efficient methyl donor.

Method 3 — Using diazomethane: Phenol reacts with diazomethane, $CH_2N_2$ (usually with a trace of an acid catalyst such as $BF_3$ or fluoroboric acid), which methylates the phenolic $-OH$ with the evolution of nitrogen gas: …