transfer reactions of Fe2adi was studied with (L-cysteine (LSH),thiourea(USH), thioglycolic acid(GSH), 2-mecarptobenzothiazole (BTSH) and benzyl (BSH)).
The stoichiometries of the reactions were 1:1 (oxidant/reductant) for LSH, GSH and BTSH while 1:2 (oxidant/reductant) was obtained for Fe2adi – USH and Fe2adi – BSH systems.
The reactions of LSH, GSH, and BTSH showed direct acid dependence and this was rationalized in terms of the protonation of the iron(III) complex in acid media. The non-acid dependence observed for Fe2adi – USH and Fe2adi – BSH systems were rationalized in terms of the deprotonation of the thiols in media.
An increase in strength resulted in a decrease in rates of reaction for the five systems. These results suggest that the rate-determining step involved oppositely charged species; thereby signifying the primary salt effect.
Added anion (CH3COO–) and cation (Mg2+) did not affect the rates of reaction for Fe2adi – LSH, Fe2adi – USH, Fe2adi – GSH and Fe2adi – BTSH systems.
Lack of dependence of the rate of reaction on added ions is likely to result from inner-sphere complex formation in accordance with the results of the ionic strength.
Enhanced rates of reaction observed for the anion and cation catalysis of Fe2adi – BSH system may be attributed to occur as a result of possible electron transfer prior to the formation of the intermediate complex.
INTRODUCTION
Background of Study
The electron transfer of binuclear iron (III) complexes have attracted a lot of interest in recent times due to their application as models for the investigation of the physiological role played by iron in biochemical processes 2, such as hemerythrin 2,3,4.6 and ferric porphyrin7,27,28 47.
Previously, the dynamics of electron transfer reactions of dinuclear oxo binged iron(III) complexes of the form [Fe2O]4+with ascorbic acid 4,þ -mercapto acetic acid5 and þ -mercaptoethylamine 6 have been investigated.
Most of these reactions followed the outer sphere electron transfer route with intervening ion-pair complexes and free radicals.
The behaviour of metal ions with respect to their electron transfer and the roles played by bridging ligands in the course of redox reaction formed the bedrock of this study.
The main advantage of this research is that the results provide additional insight into the complexities attending reactions of bridged iron(III) complexes and the extent of influence of the bridging ligand on the rate of electron transfer.
It is therefore hoped that this research will enhance the knowledge of the kinetics and mechanisms of electron transfer reactions of binuclear iron (III) complexes and other transition metal complexes with these set of thiols.
1.2 Methods of Monitoring Reaction1 Rates
The first step in kinetic analysis of a given reaction is to ascertain the stoichiometry of the reaction and to identify any side reaction.
The fundamental data of chemical kinetics are the concentrations of the reactants and products at different times after a reaction has been initiated.
The rates of most chemical reactions are sensitive to the temperature aid. In conventional experiments, the temperature of the reaction mixture must be held constant throughout the course of the reaction.
REFERENCES
Ukoha P.O., (1999), Kinetics and Mechanisms of Redox reactions of – oxo-bridged iron (III) complex ion, [Fe (HEDTA)2O]2-and some oxyanions. PhD thesis, Ahmadu Bello University,
Eigen .M and de Meyer .L (1963). In S.L, Lewis, E.S and Kleissberger, A. (Ed). Techniques of Organic Chemistry; Inter Science, New York, p. 895
E.F (1974). Fast Reactions in Solution. Black well. Oxford Campion, R.J, Purdie, N and Sutin N. (1964). Kinetics of some Related Election Transfer Reactions. Inorganic Chemistry, 3: 109-1094.
Ukoha P.O, Obasi L.N, Oluah (2010) Inner -Sphere Oxidation of Thiophenol by bis (salicylideneiminato) sulphato cerum(iv) in aqueous perchloric acid medium. International Jour.Chem.Vol.20,No 1,) 29-36;
Ukoha P.O, Iyun JF, (2005) Chem Class J 2: 51-54; Mechanism of the oxidation of 2-mercapto acetic acid by enH2 [(FeHEDTA)2O].6H2O in aqueous acid medium.
Ologunju O, Siegel D, Olojo .R. and Simoyi R.H; (2006) J. Phys. Chem.110, 2396-2410; Oxyhalogen-Sulphur Chemistry: Kinetics and Mechanism of Oxidation of N-Acetylthiourea by Chloride and Chlorine Dioxide.
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