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

Scientific paper - Original scientific paper

• Author: Ana Budimir
• Author: Tin Weitner
• Author: Ivan Kos
• Author: Davor Šakić
• Author: Mario Gabričević
• 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)

Kinetics and mechanisms of the oxidation of methoxyurea and N-methylhydroxyurea were studied
in neutral and basic aqueous solutions. The obtained pH dependences of the oxidation rates indicate
that for both hydroxyureas the reactive species are the deprotonated ones. The second order rate constants,
the activation enthalpies and the activation entropies for the reactions of methoxyurea (O-methylhydroxyurea)
and N-methylhydroxyurea anions with Fe(CN)6
3− at 25 oC, I = 2 mol dm−3 (NaClO4) were
determined as (5.06 ± 0.01) x 102 mol−1 dm3 s−1, (1.92 ± 0.02) x 104 mol−1 dm3 s−1, 27 ± 1 kJ mol−1,
16 ± 1 kJ mol−1, −101 ± 2 J mol−1 K−1, and −107 ± 4 J mol−1 K−1, respectively. The pKa value of methoxyurea
at 25 oC and 2 mol dm−3 ionic strength was determined kinetically as 12.7 ± 0.1 and the thermodynamic
parameters for the deprotonation reaction were determined as ΔaH = 43 ± 1 kJ mol−1, and ΔaS = −96 ± 4 J mol−1 K−1. When the kinetic results are compared with the data reported for hydroxyurea,
an inverse dependence of the rate constants on the pKa of the hydroxyurea derivatives at 25 oC is observed.
Such unexpected behaviour has been explained by the ab initio calculations and NBO analysis of
HOMOs for all three hydroxyureates. (doi: 10.5562/cca1799)

• Keywords (english): methoxyurea; N-methylhydroxyurea; hexacyanoferrate; oxidation; kinetics; NBO; quantum chemical study
• 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. 84, no. 2, pp. 133-147
• p-ISSN: 0011-1643
• e-ISSN: 1334-417X
• DOI: https://doi.org/10.5562/cca1799
• URN:NBN: urn:nbn:hr:163:596614
• Publication: 2011
• Document URL: https://hrcak.srce.hr/71976
• Type of resource: Text
• Access conditions: Open access
• Created on: 2020-04-17 16:31:40