Comparative kinetic investigations in ionic liquids using the MTO/peroxide system

The kinetics and thermodynamics of the reaction of methyltrioxorhenium (MTO) with hydrogen peroxide in ambient temperature ionic liquids have been studied. The rate constant for the formation of the diperoxorhenium complex, CH3ReO(eta(2)-O-2)(2), from the monoperoxorhenium complex, CH(3)Reo(2)(eta(2)-O-2), and hydrogen peroxide in [bmim]NO3 is 0.053 +/- 0.002 M-1 s(-1). The equilibrium constants for the binding of two peroxide units have been determined in [emim]BF4 to be K-1 = 110 +/- 28 and K-2 = 160 +/- 36. Similar rate constants and equilibrium constants are obtained in other water-miscible, dialkylimidazolium and alkylpyridinium ionic liquids. The values of the rate constants are highly dependent on the concentration of water in the solvent. These results indicate that the ionic liquids can behave like organic solvents and aqueous solutions of high salt concentrations. (C) 2002 Elsevier Science B.V. All rights reserved.