Thermal decomposition of nickel malonate

Abstract

Nickel malonate decomposed in vacuum at 270–340° to yield carbon dioxide and nickel carbide as the principal products and smaller amounts of methane, carbon monoxide, acetic acid and methyl acetate. The reactant did not melt during pyrolysis. On heating, the salt yielded ∼12 % of the gaseous products by an initial deceleratory process which was rapidly followed by (and partially overlapped with) the main reaction which obeyed zero-order kinetics between 20 and 90 %. Microscopic examination showed that the main reaction occurred by a nucleation and growth process in which there was a progressive increase in thickness of nuclei which were in the form of parallel laminae within the hexagonal-shaped platelets of reactant. The activation energy for the main reaction was 42.9 kcal mole^–1. Subsidiary experiments showed that reaction kinetics were little influenced by mechanical treatment of the reactant, but the short initial acceleratory portion of the main reaction became more pronounced if the product gases were removed from the reaction vessel. The nature of the decomposition transition state complex is discussed.

The kinetic characteristics of the decomposition reaction in the presence of water vapour were similar but the activation energy (32.8 kcal mole^–1) was lower. It is suggested that this reaction proceeded through hydrolysis and subsequent decomposition of malonic acid on the surface of the solid product, which was nickel oxide.