Titanium-catalyzed esterification and transesterification reactions facilitated using microwave heating

Esters can be biologically active against a range of potential targets. In addition, esterification has been used successfully to facilitate the penetration of polar compounds into cells, where the ester group can then be removed by nonspecific cellular esterases unmasking drug molecules. While direct esterification of carboxylic acids with alcohols using acid catalysts can prove effective in many cases, there are instances when substrates are acid sensitive or where the use of strong acids leads to side reactions and product decomposition. To overcome this, other methods are needed for the preparation of esters in the laboratory.

A methodology for titanium-catalyzed esterification and transesterification using microwave heating as a tool is presented. The reactions are complete within 1 h of heating at 160 °C. The substrate scope of the methodology has been investigated. It is possible to use aromatic, aliphatic and heteroaromatic acids in the esterification protocol. Acid-sensitive alcohols, including furfuryl alcohol, are also suitable substrates. For transesterification, the reaction is again amenable to microwave heating.

A range of esters can be prepared using a methodology based around the application of microwave heating and the use of a titanium catalyst.