title: Kinetics and mechanism of the oxidation of hydroquinones by a trans-dioxoruthenium(VI) complex.
abstract: The kinetics of the oxidation of hydroquinone (H(2)Q) and its derivatives (H(2)Q-X) by trans-[Ru(VI)(tmc)(O)(2)](2+) (tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) have been studied in aqueous acidic solutions and in acetonitrile. In H(2)O, the oxidation of H(2)Q has the following stoichiometry: trans-[Ru(VI)(tmc)(O)(2)](2+) + H(2)Q --> trans-[Ru(IV)(tmc)(O)(OH(2))](2+) + Q. The reaction is first order in both Ru(VI) and H(2)Q, and parallel pathways involving the oxidation of H(2)Q and HQ(-) are involved. The kinetic isotope effects are k(H(2)O)/k(D(2)O) = 4.9 and 1.2 at pH = 1.79 and 4.60, respectively. In CH(3)CN, the reaction occurs in two steps, the reduction of trans-[Ru(VI)(tmc)(O)(2)](2+) by 1 equiv of H(2)Q to trans-[Ru(IV)(tmc)(O)(CH(3)CN)](2+), followed by further reduction by another 1 equiv of H(2)Q to trans-[Ru(II)(tmc)(CH(3)CN)(2)](2+). Linear correlations between log(rate constant) at 298.0 K and the O-H bond dissociation energy of H(2)Q-X were obtained for reactions in both H(2)O and CH(3)CN, consistent with a H-atom transfer (HAT) mechanism. Plots of log(rate constant) against log(equilibrium constant) were also linear for these HAT reactions.
authors.affiliation: Department of Biology and Chemistry, City University of Hong Kong, Kowloon Tong, China.
authors.forename: William W Y
authors.initials: WW
authors.lastname: Lam
authors.forename: Mendy F W
authors.initials: MF
authors.lastname: Lee
authors.forename: Tai-Chu
authors.initials: TC
authors.lastname: Lau
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D002849:Chromatography, Gas / Q000379:methods; D006873:Hydroquinones / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012428:Ruthenium / Q000737:chemistry*; D012680:Sensitivity and Specificity; D012996:Solutions / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry
chemical_list: D000097:Acetonitriles; D006873:Hydroquinones; D009942:Organometallic Compounds; D012996:Solutions; D014867:Water; D012428:Ruthenium