The oxidation of 2-thiopyrimidine and 2-thiouracil by Ir(IV) complexes

Henry N. Po, Chang Fan Lo, Nikola Jones, Richard W. Lee

Research output: Contribution to journalArticle

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Abstract

The kinetics of the oxidation of 2-thiopyrimidine (TP) by IrCl2- 6 and IrBr2- 6, and 2-thiouracil (TU) by IrCl2- 6 follow a second-order rate law, first-order with respect to both the concentration of the oxidant and reductant. The second-order rate constants at 25.0 °C and at μ = 0.10 M are: 3.30 M-1 sec-1 for TP+IrCl3- 6 at pH 2.10, 0.187 M-1 sec-1 for TU + IrCl2- 6 at pH 2.10, and 344 M-1 sec-1 for TP + IrBr2- 6 at pH 5.3. A pH-rate profile is observed to have nearly a constant rate at pH 2.1 to 3.5 and a rapid increase in rate from pH 3.5 to 5.5. This is accounted for by the equilibrium pKa of the thiols and by the higher reactivity of the mercaptide anions The activation parameters calculated from the temperature dependence studies are: ΔH = 7.5 kcal/ mole, Δs = -31.0 e.u. for the TP + IrCl2- 6, and ΔH≠ = 10.1 kcal/mole, ΔS≠ = -27.8 e.u. for the TU + IrCl2- 6. A free radical mechanism is postulated to account for the above observed kinetics.

Original languageEnglish (US)
Pages (from-to)185-189
Number of pages5
JournalInorganica Chimica Acta
Volume46
Issue numberC
DOIs
StatePublished - Jan 1 1980
Externally publishedYes

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Thiouracil
Oxidation
oxidation
Kinetics
Free radicals
Oxidants
Rate constants
Negative ions
Chemical activation
Reducing Agents
Sulfhydryl Compounds
Free Radicals
Anions
kinetics
thiols
free radicals
Temperature
reactivity
activation
anions

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

The oxidation of 2-thiopyrimidine and 2-thiouracil by Ir(IV) complexes. / Po, Henry N.; Lo, Chang Fan; Jones, Nikola; Lee, Richard W.

In: Inorganica Chimica Acta, Vol. 46, No. C, 01.01.1980, p. 185-189.

Research output: Contribution to journalArticle

Po, Henry N. ; Lo, Chang Fan ; Jones, Nikola ; Lee, Richard W. / The oxidation of 2-thiopyrimidine and 2-thiouracil by Ir(IV) complexes. In: Inorganica Chimica Acta. 1980 ; Vol. 46, No. C. pp. 185-189.
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abstract = "The kinetics of the oxidation of 2-thiopyrimidine (TP) by IrCl2- 6 and IrBr2- 6, and 2-thiouracil (TU) by IrCl2- 6 follow a second-order rate law, first-order with respect to both the concentration of the oxidant and reductant. The second-order rate constants at 25.0 °C and at μ = 0.10 M are: 3.30 M-1 sec-1 for TP+IrCl3- 6 at pH 2.10, 0.187 M-1 sec-1 for TU + IrCl2- 6 at pH 2.10, and 344 M-1 sec-1 for TP + IrBr2- 6 at pH 5.3. A pH-rate profile is observed to have nearly a constant rate at pH 2.1 to 3.5 and a rapid increase in rate from pH 3.5 to 5.5. This is accounted for by the equilibrium pKa of the thiols and by the higher reactivity of the mercaptide anions The activation parameters calculated from the temperature dependence studies are: ΔH≠ = 7.5 kcal/ mole, Δs≠ = -31.0 e.u. for the TP + IrCl2- 6, and ΔH≠ = 10.1 kcal/mole, ΔS≠ = -27.8 e.u. for the TU + IrCl2- 6. A free radical mechanism is postulated to account for the above observed kinetics.",
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N2 - The kinetics of the oxidation of 2-thiopyrimidine (TP) by IrCl2- 6 and IrBr2- 6, and 2-thiouracil (TU) by IrCl2- 6 follow a second-order rate law, first-order with respect to both the concentration of the oxidant and reductant. The second-order rate constants at 25.0 °C and at μ = 0.10 M are: 3.30 M-1 sec-1 for TP+IrCl3- 6 at pH 2.10, 0.187 M-1 sec-1 for TU + IrCl2- 6 at pH 2.10, and 344 M-1 sec-1 for TP + IrBr2- 6 at pH 5.3. A pH-rate profile is observed to have nearly a constant rate at pH 2.1 to 3.5 and a rapid increase in rate from pH 3.5 to 5.5. This is accounted for by the equilibrium pKa of the thiols and by the higher reactivity of the mercaptide anions The activation parameters calculated from the temperature dependence studies are: ΔH≠ = 7.5 kcal/ mole, Δs≠ = -31.0 e.u. for the TP + IrCl2- 6, and ΔH≠ = 10.1 kcal/mole, ΔS≠ = -27.8 e.u. for the TU + IrCl2- 6. A free radical mechanism is postulated to account for the above observed kinetics.

AB - The kinetics of the oxidation of 2-thiopyrimidine (TP) by IrCl2- 6 and IrBr2- 6, and 2-thiouracil (TU) by IrCl2- 6 follow a second-order rate law, first-order with respect to both the concentration of the oxidant and reductant. The second-order rate constants at 25.0 °C and at μ = 0.10 M are: 3.30 M-1 sec-1 for TP+IrCl3- 6 at pH 2.10, 0.187 M-1 sec-1 for TU + IrCl2- 6 at pH 2.10, and 344 M-1 sec-1 for TP + IrBr2- 6 at pH 5.3. A pH-rate profile is observed to have nearly a constant rate at pH 2.1 to 3.5 and a rapid increase in rate from pH 3.5 to 5.5. This is accounted for by the equilibrium pKa of the thiols and by the higher reactivity of the mercaptide anions The activation parameters calculated from the temperature dependence studies are: ΔH≠ = 7.5 kcal/ mole, Δs≠ = -31.0 e.u. for the TP + IrCl2- 6, and ΔH≠ = 10.1 kcal/mole, ΔS≠ = -27.8 e.u. for the TU + IrCl2- 6. A free radical mechanism is postulated to account for the above observed kinetics.

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