A KINETIC AND MECHANISTIC STUDY OF THE THERMAL-DECOMPOSITION OF COPPER(II) OXALATE

A kinetic and mechanistic study of the thermal decomposition of copper (II) oxalate has been completed. The reaction stoichiometry was well r epresented as CuC2O4 . 0.25H2O --> 1.92CO2 + 0.06CO + 0.25H2O + [Cu 0.01C]. Reactant crystallites were below the minimum size required for resolution of surface textural detail by scanning electron microscopy . It was shown that the crystallites formed adherent aggregates and th ere was significant particle re-texturing during the latter half of th e reaction. Analytical measurements confirmed that decomposition proce eded with stepwise cation reduction (Cu2+ --> Cu+ --> Cu0). Fractional reaction (alpha)-time curves were sigmoid in shape. The acceleratory stage in the reaction obeyed the exponential law in the range 0.04 < a lpha < 0.3 and the activation energy was 140 +/- 7 kJ mol-1 (515-550 K ). The first-order reaction was obeyed in the range 0.24 < alpha < 0.9 1 and the activation energy was somewhat larger at 180 +/- 7 kJ mol-1 (515-550 K). The reaction was significantly reduced in crushed mixture s of the salt with either Cu2O or CuCl. It is concluded that reaction proceeded with intracrystalline but not comprehensive melting; perhaps local and temporary fusion within the particles took place. The decom position of copper(II) oxalate, dominant when alpha < 0.5, proceeded s omewhat more rapidly than the subsequent (alpha > 0.5) decomposition o f copper(I) oxalate. These conclusions are supported by comparative ki netic studies of the thermal decompositions of equimolar mixtures of o xalic acid with either Cu2O or CuO. There was some evidence that the r ate-limiting step was electron transfer from anion to cation.