Green and efficient removal of sulfides using oxo-peroxo tungsten(VI)-MIL-101(Cr) nanoreactor as heterogeneous recyclable catalyst

Abstract

Efficient removal of sulfide using a modified MIL-101(Cr) nanoreactor by Schiff base complex has been investigated using H2O2 as a green oxidant. In addition, a new oxo-peroxo tungsten(VI) complex has been synthesized successfully by treating WO3 with a tridentate ONO donor Schiff base ligand in the presence of H2O2. Different techniques have been used to characterize the complex, while the crystal structure was investigated using an X-ray crystallographic approach. A seven-coordinated tungsten ion with a deformed pentagonal–bipyramidal geometry was explored using single-crystal X-ray diffraction analysis. The [WO(O2)(L)(CH3OH)] (L: (E)-N'-(5-chloro-2-hydroxybenzylidene) iso nicotinohydrazide) complex has been screened for the sulfoxidation of aryl and alkyl sulfides with H2O2 as a homogeneous catalyst. Furthermore, Chloromethylated MIL-101(Cr) having a mesoporous structure has been used as a support for the immobilization of [WO(O2)(L)(CH3OH)] complex to produce a heterogeneous and recyclable catalyst. This heterogeneous catalyst is novel in its efficiency, as illustrated by its improved activity with reference to the homogeneous catalyst under the same reaction conditions. The heterogeneous structure displayed excellent reusability several times without losing activity due to covalent grafting between –CH2Cl and W(VI) Schiff base, which introduces high stable nanostructure without leaching the complex during the reaction.