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Alcohols, Phenols and Ethers — Chemistry STD 12 Science — Question

Maharashtra BoardEnglish MediumSTD 12 ScienceChemistryAlcohols, Phenols and Ethers4 Marks
Question
Write a note on Williamson’s synthesis.
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How are ethers prepared from Alkyl halides?
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How are simple ethers and mixed ethers prepared by Williamson’s synthesis?
✓

Answer

Williamson’s synthesis : When an alkyl halide (R – X) is heated with sodium alkoxide (R – O – Na), an ether is obtained, this reaction is known as Williamson’s synthesis. This method is used to prepare simple (or symmetrical) ethers and mixed (unsymmetrical) ethers.
Sodium alkoxide is obtained by a reaction of sodium with an alcohol.
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(A) Simple (Symmetrical) ether : When an alkyl halide and sodium alkoxide having similar alkyl groups are heated, symmetrical ether is obtained.
$R -\stackrel{+}{ O }-\overline{ Na }+ R - X \xrightarrow{\Delta} R - O - R + NaX$
Sodium ethoxide on heating with ethyl bromide gives diethyl ether.
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(B) Mixed (Unsymmetrical) ether : When an alkyl halide and sodium alkoxide or sodium phenoxide having different alkyl groups are heated, unsymmetrical ether (dialkyl ethers or alkyl aryl ether) is obtained.
$\begin{aligned}
& R -\overline{ O }-\stackrel{+}{ Na }+ R ^{\prime}- X \xrightarrow{\Delta} R - O - R ^{\prime}+ NaX \\
& Ar -\overline{ O }-\stackrel{+}{ Na }+ RX \rightarrow Ar - O - R + NaX
\end{aligned}$

Sodium ethoxide on heating with methyl bromide gives ethyl methyl ether.
$\underset{\text { Sodium ethoxide }}{ C _2 H _5-\overline{ O }-\stackrel{+}{ N }}+\underset{\text { methyl bromide }}{ CH _3- Br } \xrightarrow{\Delta} \underset{\text { ethylmethyl ether }}{ C _2 H _5- O - CH _3+ NaBr }$
Sodium phenoxide on heating with ethyl bromide gives ethyl phenyl ether.
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