Kinetics and Mechanism of Reduction of Tris(acetylacetonato)cobalt(III) by Hydrazine in Acid Media

Abstract

AbstractThe kinetics of reduction of tris(acetylacetonato)cobalt(III) by hydrazine in aqueous perchloric acid medium have been studied under different conditions. The complex Co(acac)3 and its protonated form Co(acac)2(acacH+) are both reduced by N2H4 with specific rate constants kR and kH,R respectively. These reactions occur concurrently with the self reduction of the complex in acid media having a specific rate constant kH. From detailed analysis of the effects of acid and hydrazine concentration on the rate, values of kH, kR and kH,R have been determined at 30°, 40° and 50°C at an ionic strength of 2 and from these the corresponding activation parameters ΔH≠ and ΔS≠ have been evaluated. The mechanism appears to involve the formation of intermediates in which N2H62+ is hydrogen bonded to Co(acac)3 and Co(acac)2(acacH+) respectively each of which possibly decomposes (rate determining) by H atom transfer from N2H62+ to the bound acetylacetonate ligand, leading to an electron transfer to cobalt(III) forming cobalt(II).