Development of a correlation equation between the diesterification of maleic anhydride and the acidic ionic liquids nature

The sustainable synthesis of dimethyl maleate via diesterification through the utilization of ionic liquid (IL) is of great importance. However, the relationship between the ILs nature and the reactivity of diesterification is still unclear. Herein, a series of ILs with different structures were selected for the comprehensive investigation of diesterification. The acidity (H₀) and Kamlet-Taft solvent parameters (hydrogen bond donor ability (α), hydrogen bond acceptor ability (β), and polarizability (π∗)) of ILs were measured by UV–Visible spectroscopy, and the effects of them on the diesterification of maleic anhydride were also studied in detail. The results indicated that not only H₀ of the IL-based catalysis system, but also its α, β, and π∗ influenced the reaction activity of diesterification. Furthermore, a quantifiable correlation was fitted between the natural logarithm of the rate constant and multiple parameters of ILs, indicating that the diesterification rate had a positive correlation with the H₀, α, and π∗, and inverse correlation with the β of the IL. A plausible synergetic reaction mechanism for the excellent performance of [(HSO₃)PMim][HSO₄] has been proposed. Overall, this work thoroughly explored the relationship between the nature of ILs on diesterification in-depth, which will reveal the nature of diesterification in detail.