Oxyfunctionalisation of adamantane using inorganic–organic hybrid materials based on isopoly and heteropoly anions: Kinetics and mechanistic studies

Abstract

Oxyfunctionalisation of adamantane with 30% aq.H2O2 in butyronitrile solvent was efficiently catalyzed by inorganic–organic hybrid materials synthesized by the immobilisation of isopoly (WOx = sodium tungstate, MoOx = sodium molybdate and VOx = sodium metavanadate) and heteropoly anions (V1 = H4[PMo11VO40]·32·5H2O,and V3 = H6[PMo9V3O40]·34H2O, STA = silicotungstic acid, TPA = tungstophosphoric acid and MPA = molybdophosphoric acid) onto mesoporous silica (SBA-15). These catalysts were well characterized by standard techniques and it was found that polyoxometalate has been retained all its bulk characteristics upon immobilisation onto mesoporous silica. Among the catalysts 10-molybdo-2-vanadophosphoric acid (H5[PMo10V2O40]·32·5H2O) immobilized onto amine-functionalized SBA-15 gave the highest activity under the conditions in the liquid phase oxidation of adamantane with 30% aq.H2O2 in butyronitrile solvent and gave mainly 1-adamantanol. Kinetic parameter measurements were performed by following initial rate approach for determining the rate dependence of the reaction. In situ UV-vis and electron paramagnetic resonance (EPR) spectroscopic studies carried out showed that the vanadium (V) superoxo intermediate species formed was responsible for the CH bond activation of adamantane to give 1-adamentanol. Based on this, a plausible mechanism for the oxidation of adamantane to 1-adamantanol has been proposed. The catalysts leaching studies carried out by following a standard procedure ruled out any contribution by the active vanadium species that could leach into the reaction medium and catalysts were truly functioned as heterogeneous catalysts.