Kinetics and mechanism of oxidation of hydroxyurea with hexacyanoferrate(III) ions in aqueous solution

Scientific paper - Original scientific paper

• Author: Ana Budimir
• Author: Erim Bešić
• Author: Mladen Biruš
• Author's institution: University of Zagreb; Faculty of Pharmacy and Biochemistry; (Department of biophysics)
• Author's institution: University of Zagreb; Faculty of Pharmacy and Biochemistry; (Department of general and inorganic chemistry)
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Chemistry; Inorganic Chemistry

Abstract (english)

<p align="justify">Hydroxyurea (HU) effectively reduces Fe(CN)₆³⁻ to Fe(CN)₆ ⁴⁻ species in neutral and basic aqueous solution via an electron transfer process that includes the formation and subsequent fading out of a free radical, U^•(U^• ≡ H₂N−C(=O)N(H)O^•). The EPR spectrum of U^• in H₂O solutions suggests that the unpaired electron is located predominantly on the hydroxamate hydroxyl-oxygen atom. Visible spectrophotometric data reveal HU as a two-electron donor. Stoichiometry of the studied reaction can be formulated
as: 2Fe(CN)₆³⁻ + NH₂CONHOH + ½H₂O → 2Fe(CN)₆⁴⁻ + CO₂ + NH₃ + ½N₂O + 2H⁺. Lack of evidence for the formation of NO probably is a consequence of fast dimerization of HNO in comparison with the rate of its oxidation, which is slow due to the low reduction potential of the Fe(CN)₆³⁻/ Fe(CN)₆⁴⁻ couple.<br/>The kinetic of oxidation of HU by Fe(CN)₆³⁻ was studied using stopped-flow technique, as a function of H⁺, HU, Fe(CN)₆³⁻ and Fe(CN)₆⁴⁻ concentrations, as well as a function of ionic strength and temperature. The kinetic results reveal that oxidation of HU by Fe(CN)₆³⁻ proceed via an outer-sphere electron-transfer process. The effect of ionic strength on the reaction rate reveals that NaFe(CN)₆²⁻ is the reacting species rather than Fe(CN)₆³⁻ ion. The rate of the redox process was found to be first order with respect to both redox reactants while the H⁺ concentration dependence make clear that U⁻ is about four orders of magnitude more reactive than HU. The formal reduction potentials for U^•/U⁻ and HU^•/HU couples were estimated from the kinetic results as +0.47 V and +0.84 V, respectively.</p>

• Keywords (english): hydroxyurea; hexacyanoferrate(III); kinetics; redox reaction; oxidation; mechanism
• Language: english
• Publication type: Scientific paper - Original scientific paper
• Publication status: Published
• Peer review: Peer review - international
• Publication version: Published version
• Journal title: Croatica Chemica Acta
• Numbering: vol. 82, no. 4, pp. 807-818
• p-ISSN: 0011-1643
• e-ISSN: 1334-417X
• URN:NBN: urn:nbn:hr:163:527961
• Publication: 2009
• Document URL: https://hrcak.srce.hr/45621
• Type of resource: Text
• Access conditions: Open access
• Created on: 2020-04-17 17:02:43