Ionic liquid catalysed synthesis of β-hydroxy ketones.

Different acidic ionic liquids (ILs; namely, 1-methylimidazolium tetrafluoroborate, 1-methylimidazolium trifluoroacetate, N-methyl-2-pyrrolidone hydrogen sulfate, N,N,N-trioctyl-n-butanesulfonic acid ammonium hydrogen sulfate, 1-methyl-3-(3-sulfobutyl)imidazolium hydrogen sulfate) and basic ILs (namely, 1,1,3,3-tetramethylguanidinium lactate and choline hydroxide) were tested as catalysts for the aldol reaction. The choline hydroxide catalysed reaction gave high yield (94.3%) and selectivity of the 4-hydroxy-4-phenylbutan-2-one after a short reaction time (15 min) at 0 °C. This article demonstrates the potential of choline hydroxide, which is a derivative of choline and a naturally occurring water-soluble essential nutrient, as a highly active and selective green catalyst.