Alumina as Acid Catalyst in the MonoMethyl Esterification of Adipic Acid: a Study of Surface Interactions

The selective protection of one of two identical functional groups in symmetrical positions in a molecule, is an important goal in organic synthesis. In this area the preparation of monoesters of symmetrical diacids represents an important challenge, mainly when the cyclic anhydrides are not readily available. Dicarboxylic acids can be monoprotected by reaction with diazomethane or dimethyl sulfate in the presence of alumina or silica gel [1]; the transesterification approach, utilizing butyl formate in octane, is also used [2]. Here, preliminary studies concerning the monoesterification of adipic acid with methanol are reported. The reaction was tested with some commercial Al2O3 powders and an ordered mesoporous alumina prepared by a surfactant assisted synthesis. The Al2O3 catalysts were characterized by different techniques including nitrogen physisorption at 77 K, temperature-programmed desorption of ammonia (NH3-TPD) and DRIFT-IR spectroscopy. The reaction, carried out at RT for 22 hrs, affords the adipic acid monomethyl ester in 57% yield and 95% selectivity. The effect of the catalyst amount and the role of the water will be discussed.