Q.Give suitable reaction to show that trans esterification is an alcoholysis reaction.

Trans-esterification exchanges the alkoxy group of an ester for that of a different alcohol; because the ester's acyl–oxygen bond is cleaved by an alcohol molecule (not water), it is, by definition, an alcoholysis reaction.

What is alcoholysis: Just as hydrolysis is the cleavage of a bond by a water molecule, alcoholysis is the cleavage of a bond by an alcohol molecule. In trans-esterification, the $C(=O)-OR$ bond of an ester is broken by nucleophilic attack of a different alcohol, $R'OH$, at the carbonyl carbon.

Reaction and mechanism: Under acid catalysis (or base, via alkoxide), the alcohol's oxygen attacks the ester carbonyl carbon to form a tetrahedral intermediate, which then expels the original alkoxide/alcohol, giving a new ester:

$RCOOR_1 + R_2OH \underset{H^+\ or\ base}{\rightleftharpoons} RCOOR_2 + R_1OH$

Concrete example: Ethyl acetate reacting with methanol (catalysed by a trace of acid or sodium methoxide) gives methyl acetate and ethanol:

$CH_3COOC_2H_5 + CH_3OH \rightleftharpoons CH_3COOCH_3 + C_2H_5OH$

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