Hydrogen atom abstraction reactions independent of C-H bond dissociation energies of organic substrates in water

Significance of oxidant-substrate adduct formation

Tomoya Ishizuka, Shingo Ohzu, Hiroaki Kotani, Yoshihito Shiota, Kazunari Yoshizawa, Takahiko Kojima

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Detailed kinetic studies on the oxidation reactions of organic substrates such as methanol with RuIVO complexes as oxidants, formed electrochemically in water, have been conducted to elucidate the reaction mechanism. The rate constants of the oxidation reactions exhibited saturation behaviours relative to the substrate concentration, regardless of the oxidants and the substrates employed. This indicates the existence of a pre-equilibrium process based on the adduct formation between the RuIVO oxidant and the substrate. Herein, we have experimentally confirmed that the driving force of the adduct formation is the hydrogen bonding between the oxidants and alcohols even in water. In addition, we have investigated the kinetic isotope effects (KIE) on the oxidation reaction using methanol and its deuterated derivatives and as a result observed moderate KIE values for the C-H bond of methanol. We have also revealed the independency of the reaction rates from the bond dissociation enthalpies of the C-H bonds of the substrates. This independency is probably derived from the tightly condensed transition state, whose energy level is strongly controlled by the activation entropy but less sensitive to the activation enthalpy.

Original languageEnglish
Pages (from-to)1429-1436
Number of pages8
JournalChemical Science
Volume5
Issue number4
DOIs
Publication statusPublished - Apr 1 2014

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Oxidants
Hydrogen
Atoms
Water
Methanol
Substrates
Isotopes
Oxidation
Kinetics
Enthalpy
Chemical activation
Electron transitions
Electron energy levels
Reaction rates
Rate constants
Hydrogen bonds
Entropy
Alcohols
Derivatives

All Science Journal Classification (ASJC) codes

  • Chemistry(all)

Cite this

Hydrogen atom abstraction reactions independent of C-H bond dissociation energies of organic substrates in water : Significance of oxidant-substrate adduct formation. / Ishizuka, Tomoya; Ohzu, Shingo; Kotani, Hiroaki; Shiota, Yoshihito; Yoshizawa, Kazunari; Kojima, Takahiko.

In: Chemical Science, Vol. 5, No. 4, 01.04.2014, p. 1429-1436.

Research output: Contribution to journalArticle

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AU - Shiota, Yoshihito

AU - Yoshizawa, Kazunari

AU - Kojima, Takahiko

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AB - Detailed kinetic studies on the oxidation reactions of organic substrates such as methanol with RuIVO complexes as oxidants, formed electrochemically in water, have been conducted to elucidate the reaction mechanism. The rate constants of the oxidation reactions exhibited saturation behaviours relative to the substrate concentration, regardless of the oxidants and the substrates employed. This indicates the existence of a pre-equilibrium process based on the adduct formation between the RuIVO oxidant and the substrate. Herein, we have experimentally confirmed that the driving force of the adduct formation is the hydrogen bonding between the oxidants and alcohols even in water. In addition, we have investigated the kinetic isotope effects (KIE) on the oxidation reaction using methanol and its deuterated derivatives and as a result observed moderate KIE values for the C-H bond of methanol. We have also revealed the independency of the reaction rates from the bond dissociation enthalpies of the C-H bonds of the substrates. This independency is probably derived from the tightly condensed transition state, whose energy level is strongly controlled by the activation entropy but less sensitive to the activation enthalpy.

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