Deep Eutectic Solvents as Sustainable Media in Maleic Anhydride Esterification: Potential and Application Analysis

Maleate esters, particularly dimethyl maleate (DMM), are pivotal platform chemicals and key intermediates in the synthesis of polymers, plasticizers, and fine chemicals. However, the conventional production via maleic anhydride (MAH) esterification is often constrained by equilibrium limitations and the use of harsh, nonrecyclable acid catalysts. In this context, deep eutectic solvents (DESs) have recently emerged as sustainable and versatile alternatives in esterification reaction, owing to tunable acidity, negligible volatility, and outstanding environmental compatibility. We systematically summarize the three synergistic roles of DESs: (i) as solvents, enhancing reactant miscibility; (ii) as catalysts, providing tunable acidity for efficient carbonyl activation; and (iii) as reactive extractants, separating byproduct water in situ to drive reactions. This intrinsic multifunctionality enables significant process intensification by coupling reaction and separation into a single unit. Based on the current research status of DMM production, the feasibility, advantages, and potential process strategies for applying DESs to DMM synthesis are thoroughly discussed. Finally, this review concludes by outlining current challenges and future research directions for MAH esterification, emphasizing the need for rational design of DESs. The findings collectively underscore the potential of DESs to revolutionize the sustainable production of maleate esters.