Selective epoxidation of dimethyl maleate to cis-epoxydimethyl succinate over solid acid catalysts

Al-MCM-41 (Si/Al = 50), Al-MCM-41 (50) supported phosphotungstic acid (HPW) and Hβ supported HPW were prepared and characterized using XRD, FT-IR, TPD (pyridine) and 31P MAS-NMR. Epoxidation of dimethyl maleate (DMM) with tert-butylhydroperoxide (TBHP) over these catalysts was studied at 60, 80, 100 and 120 °C. cis-Epoxydimethyl succinate (CEMS) and dimethyl tartrate (DMT) were the major and minor products, respectively. Forty percent HPW-Hβ zeolite was found to be more active than 20% HPW-Al-MCM-41 (50), 40% HPW-Al-MCM-41 (50), 20% HPW-Hβ zeolite and Hβ zeolite. The active sites for this reaction were ascribed to Lewis acid sites present in these catalysts. Feed ratios (DMM:TBHP) of 1:5 and 1:10 were found to give high selectivity of CEMS at maximum DMM conversion. The formation of CEMS without its trans isomer in a single step epoxidation of DMM is the salient feature of this study. The leaching of HPW from the support was not observed in this study.