Reesterification

Reesterification is a chemical process in which the ester functional group undergoes an exchange of its alkoxy substituent with another alcohol, yielding a different ester and a new alcohol. In practice, this reaction is most commonly referred to as transesterification in contemporary literature, but some sources use the term reesterification to emphasize the interchange of ester groups between substrates. The general reaction can be represented as an ester RCOOR' reacting with an alcohol R''OH to form a new ester RCOOR'' and a new alcohol R'OH. More broadly, any exchange of the alkoxy groups among esters and alcohols can be described this way.

Mechanistically, reesterification proceeds via nucleophilic acyl substitution at the carbonyl carbon. A nucleophilic alcohol attacks the carbonyl, forming a tetrahedral intermediate that collapses to expel the leaving alkoxide, generating the new ester. The rate and outcome depend on the leaving group ability of R' and the nucleophilicity of the incoming alcohol, as well as the reaction conditions and catalyst. Reesterification can be catalyzed by acids (for example sulfuric acid or p-toluenesulfonic acid), bases (such as alkoxides), or enzymes (lipases) in milder conditions.

Applications include polymer and natural-product synthesis, the preparation of esters with specific alkyl groups, and processes in biodiesel production wherein esters exchange partners with short-chain alcohols. Because the reaction is typically reversible, removing one of the alcohol products or using excess alcohol can drive the equilibrium toward the desired ester. Safety, solvent choice, and catalyst selection are important to manage side reactions such as hydrolysis or undesired transesterification of other functional groups.