Synthesis, characterization and catalyticoxidation of para-xylene by a manganese(iii)Schiff base complex on functionalized multi-wall carbon nanotubes (MWNTs)

Abstract

In the present study, hydroxyl functionalized manganese(III) Schiff-base; [Mn((OH)₂-salophen)Cl] [(OH)₂-salophen] = (N,N′-bis(4-hydroxysalicylidene)phenylene-1,2-diamine); has been covalently anchored on modified multi-wall carbon nanotubes (MWNTs); [Mn((OH)₂-salophen)Cl]@MWNTs]. The new modified MWNTs have been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron (XPS), thermal analysis, FT-IR spectroscopy and elemental analysis. The results suggest that the symmetrical Schiff-base is a bivalent anion with tetradentate N₂O₂ donors derived from the phenolic oxygen and azomethine nitrogen. 4-Hydroxy salophen; [(OH)₂-salophen], complex of manganese, grafted on the walls of MWNTs have been investigated as catalysts for the aerobic oxidation of para-xylene in the absence of added halogen promoters and using tert-butylhydroperoxide (TBHP) as the initiator at low temperatures. The major products include toluic acid, toluyl aldehyde and toluyl alcohol. The MWNTs-grafted complex did not undergo any colour change during the reaction and could be easily separated and reused many times. In contrast, the neat complex, while they were active in the first cycle, was completely destroyed during the run and changed colour. They, however, gave lower conversions compared to the grafted catalyst.