Reactions between iron(III) and catechol (o-dihydroxybenzene). part I. Equilibria and kinetics of complex formation in aqueous acid solution
- 1 January 1973
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 23,p. 2605-2608
- https://doi.org/10.1039/dt9730002605
Abstract
The equilibria and kinetics of formation of catecholato(2–)iron(III) have been studied over the pH range 1·00–2·00 in aqueous media with the stopped-flow technique. At 25·0 °C and ionic strength 1·0M(NaClO4), the equilibrium constantKe for chelate-complex formation (i) is (4·35 ± 0·10)× l0–2 mol l–1 and ε[Fe(cat)+]=(1·25 ± 0·05)× 103l mol–1 at 700 nm. From the hydrogen-ion dependence of the reaction rate it can be shown that complex Fe3++ H2cat ⇌[Fe(cat)]++ 2H+(i), formation occurs between [FeOH]2+ ion and catechol with a rate constant k=(3·1 ± 0·2)× 103 l mol–1 s–1; estimated activation data are ΔH‡= 9·6 ± 1·0 kcal mol–1 and ΔS‡=–11·1 ± 3·0 cal K–1 mol–1. The experimental data are consistent with the accepted ld mechanism for ligand substitution.Keywords
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