Efficient synthesis of quinoxaline derivatives over ZrO2/MxOy (M = Al, Ga, In and La) mixed metal oxides supported on MCM-41 mesoporous molecular sieves

Mesoporous Si-MCM-41 was synthesized by a hydrothermal crystallisation method. Various weight percentages of ZrO2/MxOy (where M=Al, Ga, In and La) mixed metal oxides were loaded by wet impregnation using methanol solutions. The characteristic structural features of the materials were determined by various physico-chemical techniques, such as XRD, BET surface area measurement, ammonia TPD, SEM and TEM. The regular meso structure of Si-MCM-41 with a uniform pore size is very well preserved after optimum loading of binary metal oxides. XRD patterns revealed the hexagonal nature of the support; it retained its structure with maximum loading of 17 wt.% ZrO2 and 4 wt.% MxOy mixed oxides. BET measurements show the abrupt decrease in surface area, pore size and pore volume at higher loading of metal oxides. TEM studies of the material shows regular arrangement of hexagonal pores present in the host Si-MCM-41 and the fine dispersion of metal oxides over the support. NH3-TPD experiments indicated the variations in the acid strength as the metal oxides were loaded. The acid strength of the catalysts follows the order: 17% ZrO2/4% Ga2O3/MCM-41 approximate to 17% ZrO2/4% Al2O3/MCM-41 > 17% ZrO2/4% La2O3/MCM-41 > 17% ZrO2/4% In2O3/MCM-41 > 17% ZrO2/MCM-41. Medicinally important quinoxaline derivatives were efficiently synthesized by the liquid phase condensation reaction of various 1,2-diamines with 1,2-diketones using the prepared catalysts. Various reaction parameters were optimized to improve product yield. (C) 2009 Published by Elsevier B.V.