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

The thermal decomposition of copper(II) mellitate proceeds to completi on between 470 and 530 K C6(CO2)6Cu3 --> 5.5CO2 + 0.03CO + [C3C6.5O1.0 ] by two distinct rate processes. The first is acceleratory and fits t he power law (alpha1/2 = kt) to fractional reaction (alpha) = 0.45, du ring which the copper is extensively reduced (Cu2+ --> Cu+); the activ ation energy is 155 +/- 7 kJ mol-1. The second reaction is strongly de celeratory, being expressed by the third order equation; the activatio n energy is 200 +/- 15 kJ mol-1. Textural changes during reactions hav e been characterized by scanning electron microscope examinations. The salt does not show evidence of melting. The present work extends a pr evious investigation of the same reactant. Results here are discussed in the context of similar studies of copper(II) salts of other organic acids; all give evidence of stepwise cation reduction (Cu2+ --> Cu+ - -> Cu) during the two consecutive reactions. It is concluded that, unl ike other reactants in this comparison, the second step is not decompo sition of copper(I) mellitate but involves a range of condensed aromat ic anions. A short comparative survey is given of studies of the therm al decompositions of copper(II) salts of formic, oxalic, malonic, male ic, fumaric, squaric and mellitic acids.