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The oxidation of phenols, cinnamic acids and methyl aryl sulfides by hydrogen peroxide, using three catalyst systems, [L2Mn2IV(μ-O)3](PF6)2, L = 1,4,7-trimethyl-1,4,7-triazacyclononane; [LMnIV(OMe)3(PF6); and MnII/L/H2O2, have been studied. The results from a combination of spectroscopic and kinetic studies, coupled with Hammett correlations and 18O labelling experiments, suggest that with each system the active oxidant is an electrophilic, mononuclear oxo-manganese (V) species. The influence of additives that can act as co-ligands for the manganese species has been investigated, with a view to controlling the activity/selectivity of the active oxidant. The two-step, sulfide–sulfoxide–sulfone, oxidation shows an unusual switch in the philicity of the active oxidant from electrophilic in the first step to nucleophilic in the second. Mechanisms for the oxidations are proposed.

l,4,7-Trimethyl-l,4,7-triazacyclononane (TMTACN), MnSO4 and H2O2, in basic aqueous acetonitrile, is an effective system for the epoxidation of cinnamic acid. The influence of a selection of organic additives, potential co-ligands for the manganese species, on the reactions has been studied by UV–vis spectroscopy and ESI-MS. The mechanism of the most efficient system, with added oxalic acid, has been investigated in more detail using cinnamic acid and seven of its 3- or 4-substituted derivatives. A Hammett correlation of rate data shows that the active oxidant is electrophilic (ρ value −0.63). Oxygen ( 18 O ) labelling experiments reveal that H2O2 and not H2O is the source of the oxygen in the epoxide. Possible mechanisms for the reactions are discussed.

A kinetic and mechanistic study is reported of the oxidation of a number of azonaphthol dyes with hydrogen peroxide in aqueous solution, catalysed by some mono and dinuclear manganese(IV) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN). The results of UV-Vis investigations, augmented by EPR and ESI-MS studies, are described for a series of experiments in which concentrations, pH and ionic strength have been varied. The reactions are characterised by an induction period followed by a relatively rapid oxidation. For the dinuclear manganese complex 2, these are consistent with an initial perhydrolysis of the manganese complex involving both the dye anion and HO2-, to give mononuclear manganese species and the operation of a catalytic cycle incorporating MnIIIL(OH)3, O = MnVL(OH)2 and MnIVL(OH)3 (L = Me3TACN) (cf. the reactions of peroxidase enzymes). ESI-MS results provide evidence for the formation and reaction (with the dye) of MnIVL(OH)3. With the mononuclear manganese complex MnIVL(OMe)3, there is a short lag-phase attributed to perhydrolysis by HO2- followed by the same catalytic cycle.