With the rapid development in the field of synthetic
organic chemistry, researchers from both academia and
industry have started giving serious thought to the
detrimental effect of non-green processes and chemicals
on the environment. They have successfully developed
several environmentally benign procedures to avoid, or
at least minimise, these effects. Syntheses of coumarins
have been carried out successfully using solid acid
catalysts12 and by combination of solid acid catalysts
and microwave irradiation13 as an alternative to conventional
methods. Ionic liquids have recently gained
recognition as possible environmentally benign alternative
solvents in various chemical processes. They have
attracted the attention of chemists owing to their
unique physical and chemical properties.14 Because of
their vanishingly low vapour pressure, ionic species do
not contribute to volatile organic compound emission.
They have also been referred as ‘designer solvents’,15 as
their properties can be altered by the fine-tuning of
parameters such as the choice of organic cation, inorganic
anion and alkyl chain attached to the organic
cation. These structural variations offer flexibility to the
chemist to devise the most idealised solvent, catering
for the needs of any particular process. Several reactions
have been carried out in ionic liquids, such as
Diels–Alder16a,b and Wittig reaction,16c benzoin
condensations16d and hydrogenation16e reactions and
even enzyme catalysed reactions.16f