OXIDATION OF SOME COHPLEXONES BY THREE TRANSITION METAL COMPLEXES: A COMPARATIVE MECHANISTIC STUDY
OXIDATION OF SOME COHPLEXONES BY THREE TRANSITION METAL COMPLEXES: A COMPARATIVE MECHANISTIC STUDY
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Date
1992-03
Authors
MAMMAN, SARATU,
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Abstract
ABSTRACT
The kinetics and mechanisms of the oxidation of HEDTA, EDTA
and NTA by Co1IIW, Fe (bipy)3
3+ and Fe(5-H02-phen)33+ respectively
have been studied in aqueous perchloric acid media.
One mole of the complexone was found to reduce two moles of
the complex in each case. Each reaction is first-order with
respect to oxidant and reductant. For all the reactions studied,
the empirical rate law is given by
d[Ox]
= 2k2[0x][Red]
dt
at 25.0 ± 0.1-C, I = 2.0M(5aC104) and [H+] range of (0.25-1.0)M.
Where 'Ox' is CoIXIW, Fe(bipy)33+ or Fe(5-N02-phen)33+ and 'Red'
is HEDTA, EDTA or NTA.
The rates of reactions decrease with increasing [H+]. This
is attributed to the dissociation of the hydrogen of the -CO2H
group in the complexones prior to electron transfer.
Similar mechanisms have been proposed for these reactions on
the basis of the similarities in their stoichiometries and
oxidation products.
Both spectrophotometry and kinetic evidence in these
reactions indicate that an inner-sphere complex formation prior
to the electron transfer step is absent. The outer-sphere
mechanism is therefore the most plausible for the title
reactions. The inertness of these oxidants to substitution is
advanced as the major reason for the operation of the outersphere
mechanism in these reactions.
Description
DEPARTMENT OF CHEMISTRY
FACULTY OF SCIENCE
AHMADU BELLO UNIVERSITY
ZARIA, NIGERIA
Keywords
OXIDATION,, COHPLEXONES,, TRANSITION,, METAL,, COMPLEXES,, COMPARATIVE,, MECHANISTIC,, MECHANISTIC