OXIDATION OF SOME COHPLEXONES BY THREE TRANSITION METAL COMPLEXES: A COMPARATIVE MECHANISTIC STUDY

No Thumbnail Available
Date
1992-03
Authors
MAMMAN, SARATU,
Journal Title
Journal ISSN
Volume Title
Publisher
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
Citation
Collections