The oxidation of styrene and derivatives with H2O2 catalyzed by manganese porphyrins in acetonitrile is described. The effect of the imidazolium substituent on the catalytic efficiency has been also considered. The thermodynamic analysis has indicated that enthalpy rules styrene oxidation when catalysts Mn(Porph)-1 and Mn(Porph)-2 are used whereas the entropy is the driven force for Mn(Porph)-3 and Mn(Porph)-4 catalyzed reactions. Interestingly, an enthalpy-entropy compensation phenomenon is observed when comparing the thermodynamic results obtained for catalysts Mn(Porph)-3 and Mn(Porph)-4. Hammett plots for the studied manganese porphyrins provided small rho-values, and this is typical for multi-step reactions, indicating that there is no significant charge separation in the transition state. For Mn(Porph)-1 and Mn(Porph)-2 the formation of multiple active species can be put forward whereas for Mn(Porph)-3 and Mn(Porph)-4 a concerted-type mechanism, via metalloxetane intermediate, fits well with the values obtained for those catalysts. The imidazolium-based catalysts have shown to be efficient catalysts in styrene and derivatives oxidation with hydrogen peroxide. (C) 2011 Elsevier B.V. All rights reserved.