Kinetic and mechanistic analysis of oxidation of 2-furoic hydrazide by hexachloroirradate(IV) in a wide pH range

  • Haiping Yao
  • Hongwu Tian
  • Liyao Xu
  • Yanqing Xia
  • Li ZhouEmail author
  • Chunli LiuEmail author
  • Tiesheng ShiEmail author


Oxidation of 2-furoic hydrazide (FH) by hexachloroiridate(IV) ([IrCl6]2−) was studied kinetically in a wide pH range in aqueous solution of 1.0 M ionic strength. The oxidation reaction followed well-defined second-order kinetics: − d[IrCl62−]/dt = k′[FH]tot[IrCl62−], where [FH]tot denotes the total concentration of FH and k′ stands for the observed second-order rate constants. The established k′–pH profile displays that k′ increases drastically with pH and a plateau region exists between pH 4 and 6. A stoichiometric ratio of Δ[FH]tot/Δ[IrCl62−] = 1/4 was revealed by spectrophotometric titrations. 1H NMR spectroscopic studies indicated that FH was cleanly oxidized to 2-furoic acid. The kinetic data suggest a reaction mechanism in which all the three protolysis species of FH react with [IrCl6]2− in parallel, forming the rate-determining steps. Two stabilized hydrazyl radicals are generated in the rate-determining steps, in which a single electron is transferred to [IrCl6]2−. The two hydrazyl radicals react rapidly in consecutive steps requiring 3 mol of Ir(IV) to form 2-furoic acid as the final product. Rate constants of the rate-determining steps were deduced through a simulation of the rate expression to the k′–pH dependency data. Values of these rate constants demonstrate that the three protolysis species of FH have a huge reactivity span, changing by about 109 times toward reduction in [IrCl6]2− and that FH can be readily oxidized in neutral and basic media. Rapid scan spectra and the measured activation parameters suggest that an outer-sphere electron transfer is probably taking place in each of the rate-determining steps. This is the first kinetic study on the oxidation reactions of FH and provides concurrently the protolysis constants of FH (pKa1 = 3.04 ± 0.08 and pKa2 = 11.6 ± 0.1) at 25.0 °C and 1.0 M ionic strength.



Financial support of this work by a setup fund from Zaozhunag University (1020717) is gratefully acknowledged.

Compliance with ethical standards

Conflict of interest

The authors declare no conflict of interest.

Supplementary material

11243_2019_347_MOESM1_ESM.docx (3.5 mb)
Supplementary material 1 (DOCX 3549 kb)


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© Springer Nature Switzerland AG 2019

Authors and Affiliations

  1. 1.College of Chemistry and Environmental Science, the MOE Key Laboratory of Medicinal Chemistry and Molecular DiagnosticsHebei UniversityBaodingPeople’s Republic of China
  2. 2.College of Chemistry, Chemical Engineering, and Materials ScienceZaozhuang UniversityZaozhuangPeople’s Republic of China

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