Explain the following reactions:
(i) Reimer - Tiemann reaction
(ii) Williamson's ether synthesis

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Solution

(i) Reimer-Tiemann reaction:
Phenol is converted to salicyadehyde (ortho hydroxy benzaldehyde)
by treatment with NaOH/chloroform. Thus Reimer-Tiemann reaction
involves ortho-formylation of phenols.
$C_{6} H_{5} - O H a q N a O H - ----- \to C H C l_{3} o - N a^{+} O^{-} - C_{6} H_{4} - C H C l_{2} N a O H - --- \to o - N a^{+} O^{-} - C_{6} H_{4} - C H O H^{+} - - \to o - H O - C_{6} H_{4} - C H O$
Major product is ortho isomer which is separated from para isomer by steam distillation. Ortho isomer predominates due to its stability due to intramolecular hydrogen bonding.
(ii) Williamson synthesis:
It is used for the preparation of simple as well as mixed ethers. Alkyl halide is heated with alcoholic sodium or potassium alkoxide to form corresponding ethers.
$R - O N a + X - R Δ - \to R - O - R^{'} + N a X$
Thus, methyl iodide, on heating with alcoholic sodium methoxide forms dimethyl ether.
$C H_{3} - O N a + X - C H_{3} Δ - \to C H_{3} - O - C H_{3} + N a I$

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