Esterification of maleic anhydride with methanol over solid acid catalysts: a novel route for the production of heteroesters Original Research Article

Al-MCM-41 molecular sieves (Si/Al=50, 100, and 150) were synthesized hydro-thermally and characterized by XRD, FTIR, BET (surface area) and Si, Al MAS-NMR techniques. The catalytic activities of these molecular sieves and of Hβ-zeolite were tested for esterification of maleic anhydride in the liquid phase at 80, 100 and 150 °C. The reaction was observed to yield monomethylmaleate even in the absence of catalyst, as the product is strain-free, whereas the formation of dimethylmaleate required the presence of a catalyst. Among the catalysts, Hβ was found to be more active than Al-MCM-41 molecular sieves. The lower activity of Al-MCM-41 catalyst was due to pore blocking by reactants as well as by products. An interesting observation in this study is that dimethylmaleate isomerisation to dimethylfumarate is not favored. At 80 °C this isomerisation was completely absent over Al-MCM-41 molecular sieves, and was less than 1% over Hβ. The complete conversion of maleic anhydride with methanol to monomethylmaleate stands as a discovery that will help to design new routes to synthesize a wide variety of new heteroesters.