Kinetics of the reactions of Cu(0) and Cu2O in Hexanes or condensed carbon dioxide by tert-Butyl peracetate and 1,1,1-trifluoro-2,4-pentanedione.
The oxidation and removal of copper(0) foil and copper(I) oxide (Cu2O) powder were studied in hexanes or condensed CO2 (at a constant density of 0.8 g/cm3) using excess tert-butyl peracetate (t-BuPA), as the oxidant, and excess 1,1,1-trifluoro-2,4-pentanedione (tfacH), as the chelating agent from 19 to 68 degreesC. Concentration and temperature effects were used to develop kinetic models. Under our conditions, independent of solvent choice, the reaction of Cu2O was first order with respect to t-BuPA and tfacH while for Cu(0) foil the reaction was independent of t-BuPA concentration and second order with respect to tfacH. The calculated effects of stir rate and reaction temperature on the mass transfer coefficient derived from a correlation for flow past a sphere were used to confirm that the reaction was kinetically controlled along with the fact that the reaction
rates and orders were independent of stirring rate. Copper removal rates were calculated from the kinetic expressions (at 40 degreesC using 0.78 M tfacH and t-BuPA): copper from the foil was removed at 2.7 nm/min in hexanes and 140 nm/min in condensed CO2 while the Cu2O powder, based on initial surface area, was consumed at 120 nm/min in hexanes and 7.0 nm/min in condensed CO2. The Arrhenius expressions were determined by the temperature-dependent kinetics of the product, Cu(tfac)2, formation. While hexanes and condensed CO2 have similar solvent properties in many respects, the apparent activation energies, Ea, for Cu(0) foil were 88 kJ/mol in hexanes and 49 kJ/mol in CO2. The apparent Ea for Cu2O were 30 kJ/mol in hexanes and 53 kJ/mol in CO2. The differences in the activation energies are attributed to a complex combination of solvent properties and the energetics of the reacting species.
Kandula, Sunita., Harmonay, Lauren., Shodder, Philip., Bessel, Carol., Weinstein, Randy.