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Kinetics of the homogeneous reaction between formic acid and thallium (III) in aqueous solution. Halvorson, Harold Norman

Abstract

The kinetics of the oxidation of HCOOH by thallium (ill) in aqueous perchloric acid solution were studied in the temperature range 65 to 85°C. The effects of concentration variation, ionic strength, pH and various salts on the rate of reaction were determined. The kinetics suggest that the reaction proceeds through the formation of an intermediate complex Tl.HCOOH⁺⁺⁺ by the following mechanism T1⁺⁺⁺ + HCOOH ⇄T1.HCOOH⁺⁺⁺ (K fast equilibrium) T1HCOOH⁺⁺⁺ → T1⁺ + 2H⁺ + CO₂ (k slow) On the basis of this mechanism, the following rate equation was derived and found to fit the experimental data. [Equation omitted] where a and b are the initial T1⁺⁺⁺ and HCOOH concentrations, respectively, while x is the concentration of T1⁺ at time t. The constants k and K were evaluated kinetically and found to have the values: K = 16.2 liter mole¯¹ (between 65 and 85°C.) and k = 1.2 x 10¹³ exp, [-26,600/RT] sec.¯¹. The absorption spectra of the solutions also provided evidence for the presence of the postulated complex. The inhibiting effects of chloride and sulphate ions on the reaction were attributed to their ability to tie up thallium (III) by complexing with it.

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