Temperature dependence of the rate constants for reactions of the carbonate radical with organic and inorganic reductants

✍ Scribed by R. E. Huie; L. C. T. Shoute; P. Neta

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 635 KB
• Volume: 23
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550230606

✦ Synopsis

Rate constants have been measured by pulse radiolysis for the reactions of the carbonate radical, COa'-, with a number of organic and inorganic reactants as a function of temperature, generally over the range 5 to 80°C. The reactants include the substitution-inert cyano complexes of Fe", Mo", and W", the simple inorganic anions SO$-, ClOz-, NOz-, I-, and SCN-, several phenolates, ascorbate, tryptophan, cysteine, cystine, methionine, triethylamine, and ally1 alcohol. The measured rate constants ranged from less than lo5 to 3 x lo9 M-' s-', the activation energies ranged from -11.4 to 18.8 k J mol-', and the pre-exponential factors ranged from log A = 6.4 to 10.7. The activation energies for the metal complexes and inorganic anions generally decrease with increasing driving force for the reaction, as expected for an outer sphere electron transfer. For highly exothermic reactions, however, the activation energy appears to increase, probably reflecting the temperature dependence of diffusion. For many of the organic reactants, the activation energies were low and independent of driving force, suggesting that the oxidation is via an inner sphere mechanism.