Comparison of two MCM-41 grafted TEMPO catalysts in selective alcohol oxidation

A new heterogeneous system for catalytic oxidations has been developed by immobilising TEMPO onto ordered mesoporous silica (MCM-41-type). The immobilisation was performed according to different methods: (i) direct grafting of the silica surface with 3-(trimethoxysilyl)propyloxy-TEMPO obtained by coupling LC-hydroxy-TEMPO and allyl bromide followed by hydrosilylation; (ii) coupling of 4-carboxy-TEMPO with 3-aminopropylsilane previously grafted on the mesoporous silica surface; (iii) coupling of the N-succinimide ester of 4-carboxy-TEMPO with the same previously grafted 3-aminopropylsilane. Efficiency and anchoring of the TEMPO were studied by various spectroscopic techniques. The textural characteristics of the mesoporous support were preserved during the different modifications. Catalytic tests on the use of the materials in the oxidation of primary alcohols proved their activity and stability under the reaction conditions. (C) 2001 Elsevier Science B.V. All rights reserved.