Catalytic Hydroxylation of Benzene to Phenol by Dioxygen with an NADH Analogue

Kensaku Hirose, Kei Ohkubo, Shunichi Fukuzumi

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21 Scopus citations

Abstract

Hydroxylation of benzene by molecular oxygen (O2) occurs efficiently with 10-methyl-9,10-dihydroacridine (AcrH2) as an NADH analogue in the presence of a catalytic amount of Fe(ClO4)3or Fe(ClO4)2with excess trifluoroacetic acid in a solvent mixture of benzene and acetonitrile (1:1 v/v) to produce phenol, 10-methylacridinium ion and hydrogen peroxide (H2O2) at 298 K. The catalytic oxidation of benzene by O2with AcrH2in the presence of a catalytic amount of Fe(ClO4)3is started by the formation of H2O2from AcrH2, O2, and H+. Hydroperoxyl radical (HO2.) is produced from H2O2with the redox pair of Fe3+/Fe2+by a Fenton type reaction. The rate-determining step in the initiation is the proton-coupled electron transfer from Fe2+to H2O2to produce HO.and H2O. HO.abstracts hydrogen rapidly from H2O2to produce HO2.and H2O. The Fe3+produced was reduced back to Fe2+by H2O2. HO2.reacts with benzene to produce the radical adduct, which abstracts hydrogen from AcrH2to give the corresponding hydroperoxide, accompanied by generation of acridinyl radical (AcrH.) to constitute the radical chain reaction. Hydroperoxyl radical (HO2.), which was detected by using the spin trap method with EPR analysis, acts as a chain carrier for the two radical chain pathways: one is the benzene hydroxylation with O2and the second is oxidation of an NADH analogue with O2to produce H2O2.

Original languageEnglish
Pages (from-to)12904-12909
Number of pages6
JournalChemistry - A European Journal
Volume22
Issue number36
DOIs
StatePublished - 26 Aug 2016

Bibliographical note

Publisher Copyright:
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Keywords

  • hydroxylation
  • oxidation
  • oxygen
  • radical reactions
  • reaction mechanism

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