Kinetics of redox mediator tris(4-bromophenyl)amine in acetonitrile and ionic liquid [BMIm][PF6]: Oxidation of benzyl and cyclohexyl alcohols

Ajith C. Herath, James Y. Becker

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6 Scopus citations


A reversible one-electron oxidation of tris(4-bromophenyl)amine (TBPA) in acetonitrile or 1-butyl-3-methylimidazoliumhexafluorophosphate [BMIm][PF6] media unambiguously generates the cation-radical (TBPA{radical dot}+), and its reduced form is catalytically regenerated in a follow-up chemical reaction with benzyl alcohol in the presence of 2,6-lutidine. The electron-transfer kinetics for these transformations has been investigated by a detailed comparison of the results obtained in both media. The apparent standard heterogeneous rate constant kapp0 for an interfacial single-electron transfer of the mediator in acetonitrile containing 0.1 M Et4NClO4 was estimated using cyclic voltammetry (CV) profiles within a wide range of sweep rates (20-1000 mV s-1). The slightly higher kapp0 value for the TBPA/TBPA{radical dot}+ couple at a Pt electrode surface was found to be (2.1 ± 0.8) 10-2 cm s-1 compared to (1.4 ± 0.6) 10-2 cm s-1 at a glassy carbon (GC) surface. kapp0 values estimated in [BMIm][PF6] are comparatively two orders of magnitude lower (6.6 ± 0.5 × 10-4 cm s-1 and 4.9 ± 0.4 × 10-4 cm s-1 at Pt and GC, respectively). It has been found that the second-order homogeneous rate constant for the oxidation of benzyl alcohol by TBPA{radical dot}+ in acetonitrile (12.10 M-1 s-1) was estimated to be greater by one order of magnitude than that in ionic liquid [BMIm][PF6] (4.20 M-1 s-1). Similar experiments carried out for the oxidation of 2-chlorobenzyl alcohol, 4-tert-butylcyclo hexanol and 4-methylcyclohexanol by the TBPA{radical dot}+ showed no noticeable catalytic effect due to large potential difference of the mediator (Ep/2 = 0.74 V vs. Fc/Fc+), compared with those of the substrates.

Original languageEnglish
Pages (from-to)98-104
Number of pages7
JournalJournal of Electroanalytical Chemistry
Issue number1-2
StatePublished - 15 Jul 2008


  • Apparent standard rate constant
  • Catalytic current
  • Ionic liquid
  • Tris(4-bromophenyl)amine

ASJC Scopus subject areas

  • Analytical Chemistry
  • Chemical Engineering (all)
  • Electrochemistry


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