FUW TRENDS IN SCIENCE & TECHNOLOGY JOURNAL
(A Peer Review Journal)
e–ISSN: 2408–5162; p–ISSN: 2048–5170
keywords: Iron(III) dimer, kinetics, L-ascorbic acid, mechanism, reduction, saloph
The kinetics and mechanism of the reduction of iron(III) dimer, [(Fe(saloph))2-µ-dicarpy] by L-ascorbic acid (H2A), in perchloric acid has been studied spectrophotometrically at λmax = 424 nm. The stoichiometric studies showed that 1 mole of H2A is oxidized for every mole of [(Fe(saloph))2-µ-dicarpy] reduced. Under pseudo-first order conditions of concentrations of [H2A] >> [(Fe(saloph))2-µ-dicarpy], the order with respect to [(Fe(saloph))2-µ-dicarpy] is unity and half-order with respect to H2A as plot of logkobs versus log[reductant] showed linearity to about 85% extent of reaction. Second order rate constant (k2) were determined as the ratio of kobs to [H2A] and was found to be fairly constant. Reaction rate was inversely dependent on acid concentration and rate increased with increase in ionic strength of reaction system. Also, increase in dielectric constant of the reaction medium (D) decreased rate of reaction and addition of CH3COO-, SO , NO or Cl- catalyzed the rate of reaction. Activation parameters evaluated gave Ea = 14.805, ∆H* = 12.122 kJmol-1 and ∆S* = -268.86 JK-1mol-1. The rates are consistent with mechanism involving the formation of free radicals and precursor complex prior to electron transfer. Michaelis-Menten plot of 1/kobs versus 1/[reductant] was linear with positive intercept for the system. The rate law is given as; (-d [Fe2-µ-dicarpy4+])/dt = (k3 + KaK1k1[H+]-1) [Fe2-µ-dicarpy4+][H2A]. The reduction of [{Fe(saloph)}2µ-dicarpy] by H2A is rationalized in terms of ion-pair complex formation with outer sphere character.
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