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WILLIAMSONS SYNTHESIS

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WILLIAMSON ETHER SYNTHESIS

Preparation of ether (sym, unsym) by 2N

S reaction between alkoxide and alkyl halide

( or alkyl sulphonate (or) sulphate) is known as williamson ether synthesis

' ' R ONa R L R O R Na L

+ + +

Solution of alkoxide can be prepared from alcohol and NaH.

2 R O H NaH R O Na H

+ +

Best results are obtained when the alkyl halide, sulphonate ( - OSO2R ) (or) sulphate ( - OSO2OR ) is

primary (or methyl).

If the substrate is tertiary, elimination is the exclusive result substitution.

Substitution is also favoured over elimination at lower temperature.

Even secondary alkyl halides are of little use.

Alkoxides are strong bases and the elimination reaction is a predominant side reaction when sec. halide

is used.

2

3 2 2 3 2 3 2 2 2 3

S NCH CH CH O Na CH CH I CH CH CH O CH CH +

(70%)

3 23 3 3 2 3 3

CH CH O Na

H C CH CH H C CH CH H C CH CH

= +

Br

75%2 3

O CH CH

(25%)

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WILLIAMSONS SYNTHESIS

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If alkoxide is a ter-alkoxide, all types of alkyl halides (except methyl halide) always give elimination

reaction, because the alkoxide is a very strong base

Halo alcohols undergo intermolecular williamson ether synthesis

MAKING OF OXIRANES:

OH

Cl

/ NaOH HOH

O

Cl

2S N

O

Oxirane