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The kinetics of the reaction between cupric acetate and molecular hydrogen in aqueous solution Dakers, Ronald Gill

Abstract

A kinetic study was made of the reaction between cupric acetate and hydrogen in aqueous solution. The reaction was followed by determining the concentration of cupric acetate remaining in solution and was found to proceed in accordance with the equation 2CuAc₂ + H₂ + H₂O → Cu₂O + 4HAc The reaction was found to be second order kinetically, the rate being proportional to the concentrations of cupric acetate and molecular hydrogen. It was established that the reaction is homogeneous, both the stainless steel vessel and the cuprous oxide product being without effect. The rate increased slightly when sodium or ammonium acetate in concentrations of 0.25 moles per liter was added to the solution but remained unchanged with further addition of these salts. The rate was also independent of the concentration of acetic acid and the pH of the solution over a wide range. The activation energy was found to be 23,400 cal. per mole and the frequency factor 1.0 x 10¯¹²1.mole¯¹ sec.¯¹ corresponding to an entropy of activation of - 5.9 cal. mole¯¹ deg.¯¹. The following mechanism has been proposed to account for these kinetic results, the first step in the reaction sequence being rate determining 1. CuAc₂ + H₂ → CuAc₂ . H₂ slow 2. CuAc₂ . H₂ + CuAc₂ → 2CuAc + 2HAc fast 3. 2CuAc + H₂O → Cu₂O + 2HAc fast This appears to be the first established instance of a homogeneous hydrogenation reaction in aqueous solution.

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