KINETICS AND MECHANISMS OF THE ELECTRON TRANSFER REACTIONS OF DIAQUOTETRAKIS (2, 2’- BIPYRIDINE)-μ-OXODIRUTHENIUM(III) IONS AND SOME REDUCTANTS IN AQUEOUS MEDIUM
KINETICS AND MECHANISMS OF THE ELECTRON TRANSFER REACTIONS OF DIAQUOTETRAKIS (2, 2’- BIPYRIDINE)-μ-OXODIRUTHENIUM(III) IONS AND SOME REDUCTANTS IN AQUEOUS MEDIUM
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Date
2015-10
Authors
MOHAMMED, Yahaya
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Abstract
The kinetics and mechanisms of the electron transfer reactions of diaquotetrakis (2, 2’-
bipyridine)-μ-oxodiruthenium(III) ions (hereafter denoted as Ru2O4+or [(H2O)2Ru2O]4+ )
and thiourea (TU),N–methylthiourea (MTU), N–allylthiourea (ATU), N,N’-
dimethylthiourea(DMTU) (collectively denoted by TSH), thiosulphate ions (S2O3
2–),
dithionite ions (S2O4
2–), hypophosphorous acid (H3PO2), methanol (CH3OH), ethanol
(C2H5OH) and propanol (C3H7OH) (collectively denoted as ROH) were studied in
aqueous perchloric acid (HClO4) medium (except for S2O4
2– and the alcohols) at I =
0.5 mol dm–3 and T = (31.0 ± 1) °C. The stoichiometry was found to be 1:2 (Ru2O4+/
reductant) in the TSH and S2O3
2–systems but 1:1 in the S2O4
2–, H3PO2 and ROH
systems. The rate of reaction is first order in oxidants and reductants for all the systems.
Addition of acid has inverse effect on the rates of reaction for the TSH system, but
direct dependence for the S2O3
2– system. The overall rate equation for the TSH reaction
can be given as :
- [Ru2O4+] = (a + b[H+]-1 )[Ru2O4+][Reductant] .
while that for S2O3
2– reaction can be given as:
- [Ru2O4+] = (a + b[H+])[Ru2O4+][S2O3
2-]
Varying the ionic strength (I) and dielectric constant (D)of the reaction medium had no
effect on rates of reaction for the TSH, S2O4
2-, H3PO2 and ROH reactions, while for the
S2O3
2– reaction, increase in I led to a decrease in rate while decrease in D led to increase
in rate of reaction. Added ions had no effect on the TSH and H3PO2 reactions but led to
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catalysis and/ or inhibition in S2O32–, S2O42- and ROH systems. Free radicals were identified in the TSH, H3PO2 and ROH reactions only. Spectroscopic information and the results of the Michaelis – Menten plots suggest the lack of formation of intermediate complex prior to electron transfer for all the systems. For all the reactions, [(H2O)2(bipy)2Ru]2+ was found to be the product of Ru2O4+ reduction. For the TSH reaction, disulphides was found to be the oxidation product of TSH while, for H3PO2 reaction, test for phosphorous acid (H3PO3) presence was positive and for the ROH system, test for aldehydes was also positive. The order of reactivity for the TSH system is ATU > DMTU > MTU > TU, while the order of reactivity for the sulphur oxyanions’ reactions is S2O42-> S2O32– and that for the ROH reactions is CH3OH > C2H5OH > C3H7OH. Based on the Michaelis–Menten plots and the interactions with added ions, all the reactions are proposed to have proceeded through the outer–sphere electron transfer mechanism. Plausible mechanisms for all the reactions have been proposed
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY ZARIA, IN PARTIAL FULFILLMENT FOR THE AWARD OF Ph.D. INORGANIC CHEMISTRY
DEPARTMENT OF CHEMISTRY
AHMADU BELLO UNIVERSITY
ZARIA
Keywords
KINETICS AND MECHANISMS,, ELECTRON TRANSFER REACTION,, DIAQUOTETRAKIS,, (2, 2’- BIPYRIDINE)-μ-OXODIRUTHENIUM(III),, IONS,, REDUCTANTS,, AQUEOUS MEDIUM