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Kinetics of the reaction between hydrazobenzene and iodine in aqueous ethanol solutions May, John Walter


The kinetics of the oxidation of hydrazobenzene by iodine in buffered ethanol-water solutions were studied between 0°C. and 25°C. A measurable rate was obtained by depressing the iodine concentration by the addition of excess iodide, so that most of the iodine was transformed to triiodide. The effects of initial concentrations, acidity, solvent composition and buffer ionic strength were determined, as well as that of adding quinone and several metal salts. Both iodine and triiodide were found to oxidize hydrazobenzene, but iodine Is about 100,000 times more reactive than triiodide. [formula omitted] The kinetics suggest that both reactions have a simple bimolecular mechanism, expressed by the rate law [formula omitted] The constants k₁ and k₂ were evaluated in 60 volume per cent ethanol and buffer ionic strength 0.31 as [formula omitted] In connection with this work it was found necessary to evaluate the equilibrium constant of formation of triiodide in the solvents used. The heat and entropy of formation from iodine and iodide in 60 volume per cent ethanol were found to be -9.5 ± 0.5 kcal.mol.⁻¹ and -13.2 e.u. respectively.

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