Applied Catalysis A: General 267 (2004) 77–86 Esterification of maleic anhydride with methanol over solid acid catalysts: a novel route for the production of heteroesters M. Bhagiyalakshmi, K. Shanmugapriya, M. Palanichamy, Banumathi Arabindoo, V. Murugesan ∗ Department of Chemistry, Anna University, Chennai 600025, India Received in revised form 18 February 2004; accepted 23 February 2004 Available online 9 April 2004 Abstract Al-MCM-41 molecular sieves (Si/Al = 50, 100, and 150) were synthesized hydro-thermally and characterized by XRD, FTIR, BET (sur- face area) and Si, Al MAS-NMR techniques. The catalytic activities of these molecular sieves and of H-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, H 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 H. 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. © 2004 Elsevier B.V. All rights reserved. Keywords: Maleic anhydride; Dimethylmaleate; Ethylmethylmaleate; Al-MCM-41; Esterification; Zeolite  1. Introduction Mesoporous molecular sieves have become materials that enjoy widespread use as catalysts in recent years in many re- actions of industrial importance. Friedel–Crafts alkylations and acylations are successfully carried out over Al-MCM-41 molecular sieves [1,2]. Acetalization, Beckmann rearrange- ment and aldol condensation are a few of many reactions thoroughly studied with these catalysts [3,4]. Acylation of alcohol with acetic anhydride to yield es- ters is an industrially important reaction, as the esters are extensively used as solvents for cellulose, oils, gums, resins etc. and as plasticizers. They also serve as raw materials for the production of artificial flavors and fra- grances [5]. Liquid-phase acid catalysts such as sulphuric acid, p-toluenesulphonic acid, methane sulphonic acid, and hydrochloric acid are commonly used catalysts for such reactions. Mineral acid catalysts are corrosive, and others ∗ Corresponding author. Tel.: +91-44-22200660; fax: +91-44-22200660. E-mail address: v murugu@hotmail.com (V. Murugesan). have product recovery problems. In most of the industrial processes, AlCl 3 and ZnCl 2 are the catalysts commonly used in stoichiometric amounts for these reactions. But these catalysts generate heavy metal wastes. Hence there has been interest to use solid acid catalysts such as zeolites which are ecofriendly and recyclable. Al-MCM-41 materi- als with large pore diameters (20–100 Å) and very scattered distribution of acid sites were proved to be important cata- lysts. Recently Hoster et al. have reported esterification of acetic acid with ethanol over MCM-41 [6]. Diaz et al. have reported combined alkylation and sulphonic acid functional- ization of MCM-41-type silica for esterification of glycerol with fatty acids [7]. These studies have motivated us to study esterification of maleic anhydride with methanol over Al-MCM-41 molecular sieves. The ester, dimethylmaleate, is used as an additive and an intermediate for plastics, pig- ments, pharmaceuticals and agriculture products. In organic synthesis it is used as a dienophile in Diels–Alder reaction. Dimethylmaleate is manufactured by reacting maleic anhy- dride with methanol in the presence of catalytic quantities of sulphuric acid [8]. As the present manufacturing process involves hazardous mineral acids, ecofriendly solid acid cat- 0926-860X/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2004.02.025