Inexpensive and tuneable protic ionic liquids based on sulfuric acid for the biphasic synthesis of alkyl levulinates

Alkyl levulinates are bio-derived chemicals, increasingly popular for their uses as solvents, additives and intermediates. However, efficient and recyclable catalysts for their synthesis are still the subject of intensive research. In this study, a wide range of alkyl levulinates was synthesized under mild conditions (room temperature, atmospheric pressure), using inexpensive and efficient Brønsted acidic ionic liquids (ILs) based on sulfuric acid and off-the-shelf bases. Acidity of the ILs was closely related to their activity. The ILs could be easy separated and recycled, without significant changes in conversion or selectivity over 10 cycles (yields ca. 90–95%). Under optimized conditions, a 99% yield of pentyl levulinate (model reaction) was achieved. The method was demonstrated to be efficient in the synthesis of levulinates of C1-C16 linear, branched and cyclic alcohols. This innovative, green route to alkyl levulinates fits well within the sustainable development strategy.