Oxidation of hydrocarbons. 12. Kinetics and mechanism of the oxidation of trans-cinnamic acid by ruthenate and perruthenate ions

Abstract

Recent theoretical calculations by Rappé and Goddard have pointed to the importance of spectator oxo groups in stabilizing intermediates produced during the reduction of high-valent transition metal oxides; intermediates which contain triply-bonded metal oxo groups are predicted to be unusually stable. In an attempt to test these conclusions experimentally, the rates of oxidation of cinnamate ion by ruthenate and perruthenate ions have been studied. Since the most likely intermediate formed from perruthenate ion (but not ruthenate ion) would contain a stabilizing, triply-bonded spectator oxo group, it would be expected to react faster if the calculations are correct. In agreement with these predictions, it was found that the activation energy (ΔG‡) for the ruthenate reaction was about 7 kcal/mol higher than for the corresponding perruthenate reaction.