Transesterification is the process of exchanging the organic functional group R″ of an ester with the organic group R' of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst. The reaction can also be accomplished with the help of other enzymes, particularly lipases (one example is the lipase E.C.3.1.1.3).
Strong acids catalyse the reaction by donating a proton to the carbonyl group, thus making it a more potent electrophile, whereas bases catalyse the reaction by removing a proton from the alcohol, thus making it more nucleophilic. If the alcohol produced by the reaction can be separated from the reactants by distillation this will drive the equilibrium toward the products, this means that esters with larger alkoxy groups can be made from methyl or ethyl esters in high purity by heating the mixture of ester, acid/base, and large alcohol.
Transesterification is used to synthesize enol derivatives, which are difficult to prepare by other means. Vinyl acetate, which is cheaply available, undergoes transesterification, giving access to vinyl ethers:
- ROH + AcOCH=CH2 ? ROCH=CH2 + AcOH
The reaction can be effected with high enantioselectivity when mediated with a lipase.
