The thermal decomposition of salts of mellitic acid. Part III. Chromic, manganous, cupric, and zinc mellitates

Abstract

Kinetic measurements for the thermal decomposition reactions of manganous, cupric, and zinc mellitates and a chromic–mellitic acid complex are reported. None of these substances melted during decomposition in vacuo but the kinetic data for rate processes fitted equations which were characteristic of reactions occurring in the homogeneous phase. The manganous and chromic compounds decomposed through two rate processes occurring in different temperature ranges; the complete decomposition of the cupric and zinc salts occurred in a single reaction. Mechanisms to account for these observations are discussed.

Evidence is presented which demonstrates that activation energies for the decomposition of mellitates can be correlated with the heat of formation of the appropriate metallic oxide. From this it is concluded that the rate-determining step in mellitate decomposition involves rupture of the carboxyl group–metal bond. The results obtained for mellitates are compared with available measurements for the reactions of bivalent metal oxalates.