Development of environmentally friendly catalytic reaction system for selective hydrocarbons oxidation

Research Project , Research Report 2004

Noritaka MIZUNO Dept. of Applied Chemistry, The Univ. of Tokyo

Abstract

A dinuclear peroxotungstate, K2[{W(=O)(O2)2(H2O)}2(m-O)]・2H2O (W2), worked as an effective epoxidation catalyst using H2O2 in water under mild reaction conditions. Further, we synthesized inorganic-organic hybrid support materials by covalently anchoring ionic liquid fragments onto the SiO2 to immobilize W2 for the development of recoverable and recyclable epoxidation catalysts.
Various kinds of allylic alcohols could be epoxidized in high yields by the use of W2 and H2O2 in water. The structural stability of catalyst W2 was confirmed by direct observation of the reaction solution with in-situ IR and UV-vis spectroscopy. It is notable that W2 could be reused for the epoxidation without loss of the high catalytic performance.
In order to immobilize W2 on the solid support, a novel anion-exchangerable solid support was designed and synthesized. The condensation of dihydroimidazolium based ionic liquid (1) and SiOH groups on the surface of SiO2 yielded the desired inorganic-organic hybrid support (1-SiO2). The prepared ionic liquid-grafted silica 1-SiO2 could act as an anion exchanger, that is, W2 could be immobilized onto 1-SiO2 via anion exchange (W2/1-SiO2).
The catalytic activity of W2/1-SiO2 was compared with that of the corresponding homogeneous analogue of [n-C12H25N(CH3)3]2[{W(=O)(O2)2(H2O)}2(m-O)] (DTMA-W2) under the same conditions. The reaction rates by the use of W2/1-SiO2 were comparable to those of DTMA-W2. This fact indicates that the homogeneous catalysis can be heterogenized with retention of the W2 catalyst performance by the supporting on ionic liquid-modified SiO2.

Keywords:

Hydrogen peroxide, Selective oxidation, Dinuclear peroxotungstate, Anion exchanger, Solid catalyst