Sodium bicarbonate assisted oxidation, by H2O2, of styrene and cyclohexene using polymer grafted dioxidomolybdenum(VI) complex as a catalyst

Abstract

Ligand H2hap-iah (I), obtained by the condensation of equimolar amounts of o-hydroxy acetophenone (hap) and indole-3-acetic hydrazide (iah) reacts with [MoVIO2(acac)2] in 1:1 ratio in refluxing methanol to give [MoVIO2(hap-iah)(MeOH)] (1). Complex 1 has been grafted in chloromethylated polystyrene cross-linked with 5% divinylbenzene {now abbreviated as PS-[MoVIO2(hap-iah)(MeOH)] (2)} via covalent bonding through imino nitrogen of the indole group. Both complexes are characterized by various spectroscopic techniques (IR, electronic, 1H, and 13C NMR), analytical and thermal studies. Complex 2 has also been analyzed by atomic force microscopy (AFM), field-emission scanning electron micrographs (FE-SEM) as well as energy dispersive X-ray (EDAX) studies. The polymer-grafted compound 2 was used for the catalytic oxidation of styrene and cyclohexene in the presence of NaHCO3 using aqueous H2O2 as oxidant. The intermediate peroxido species, expected to be involved during catalytic action, was also generated from the solution of 1 and studied by UV–vis. Various reaction conditions were considered to optimize reactions conditions for the maximum oxidation of substrates. Styrene under optimized reaction conditions gave mainly styrene oxide as a major product. Oxidation of cyclohexene gave cyclohexene oxide selectively. The polymer-grafted complex shows higher conversions than its neat counterpart. The polymer-grafted complex provides additional advantage over its homogeneous counterpart in terms of increased catalyst lifetime and easier separation from the reaction mixture and allows for recyclable catalytic system.