The thermal decomposition of cobalt phthalate and some observations on the decomposition of cobalt benzoate

Abstract

The thermal decomposition of solid cobalt phthalate proceeded through two successive rate processes which were studied in the ranges 280–370° and 400–500°. The low temperature decomposition yielded about half the available carbon dioxide, by a reaction which obeyed the first order kinetic equation, and a solid in which no crystalline phase was detected. The activation energy was 41·5 ± 2sd0 kcal mole −1. The high temperature reaction yielded oxides of carbon, benzene, other organic compounds and metallic cobalt. The formation of gaseous products exhibited the sigmoid-shaped fractional decomposition-time relationship which is characteristic of a reaction mechanism involving nucleation followed by growth of a solid product phase, probably cobalt metal. The data fitted the Avrami-Erofeyev equation with n = 3 and the activation energy was 38·5 ± 2·0 kcal mole −1. Discussion of the reaction mechanism includes comparisons with data for basic ferric and nickel phthalates. Complete decomposition of cobalt benzoate also involved two consecutive reactions; the present work was almost entirely confined to the first of these, which occurred in a melt. This reaction obeyed first order kinetics, was relatively insensitive to reactant composition and had an activation energy of 46·6 ± 2·5 kcal mole.