KINETICS AND MECHANISMS OF THE OXIDATION - REDUCTION AND THE SUBSTITUTION REACTIONS OF SOME METAL ION COMPLEXES IN ACID SOLUTION.

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Date
1982-08
Authors
IYUN, JOHNSON FEMI
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Abstract
The kinetics and mechanism of the oxidation of Ti(H20)g and Ti -edta by aqueous solutions of bromine and iodine has been investigated. At T = 25°C, I = 1.0M-(CFgS03-Li+ + CF3S03H)[H+] m 0.034 - 0.274M and X = 453nm, the rate equation 3 + for the oxidation of Ti(H20)6 by bromine was found to be: Z^ [ B r i = _JS| [Br9][Ti(lll)] + ——^ [Ti(lll)][Br:] d t 2 T [H +] + K [H ] + K 6 where k = 9.2 x 10- 3M- 1s- 1 and K = 4.5 x 10~3M. At [H ] = 1.0M, [Br-]. ='0.05 - 0.4M, the apparent second-order rate constant decreases as [Br-] increases. From the analysis of the data under these conditions, values of the second-order 2+ - rate constants for the oxidation of Ti(H20)fi by Br2 and Br„ were computed to be (3.88 ± °-4> x iP2*f" s" and (29.4 ± l.DM'V1 respectively. The rate equation for the oxidation of Ti(H20)6^+ by iodine was found to be, j r T -i — = kl Ka [Ti(lll)][I0] + k2 Ka [Ti(lll)][II]. j. & i> [H+] + Ka [H+] •+ Ka For the conditions [H+] = 0.0036 - 0.20M, 1= 1.OM (LiCl), T=25°C and X = 468m, k, = 5.3 x 102M-1s-1 kn = 6.9M-1s-1 and K • 3.2 x 10-3M.' The apparent second-order rate constant for the oxidation 111 of Ti -edta by bromine and iodine showed a biphasic dependence on pH in the range pH = 0.5 - 6.0 for bromine and pH = 0.15 - 7.45 for iodine. Below pH = 2.5, the second-order rate constant is independent of pH but for pH > 2.5 the rate constant increases with pH.
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A thesis submitted to the Postgraduate School, Ahmadu Bello University, in fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry.
Keywords
KINETICS, MECHANISMS, OXIDATION, REDUCTION, SUBSTITUTION, REACTIONS, METAL, COMPLEXES, ACID, SOLUTION
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