Abstract We have developed a simple and efficient method for the esterification of various organic acids with C4–C18 alcohols using the 1??octyl??3??methylimidazolium tetrafluoroborate–para??toluenesulphonic acid (OMIM/BF4–PTSA) couple, without organic solvent, either by classic heating or by microwave irradiation. The utilisation of the OMIM/BF4–PTSA couple presents considerable advantages: high yield, low temperature, ...