THE EFFECT OF TEMPERATURE, CATALYSIS, AND DIELECTRIC CONSTANT IN THE KINETICS OF THE OXIDATION-REDUCTION REACTIONS OF [N-(2-HYDROXY-ETHYL)ETHYLENEDIAMINE-N’,N’,N’,-TRIACETATO COBALT (11)] BY Cu2+ CATION

ABSTRACT

The effects of temperature, dielectric constant and catalysis in the kinetics of the oxidation –reduction reactions (involving electron transfer) of N-(2-hydroxy-ethyl) ethylenediammine– N’,N’,N’-Triacetatocobalt (II) by Cu²⁺ cation were determined.  The dielectric constant was decreased from 63.05 to 43.18 and it was found that the rates of the reaction did not show any appreciable change. This seems to mean that the change in the dielectric constant of the medium had no effect on the rates of reaction in this [Co^IIHEDTAH₂O]^– and Cu²⁺ systems. At constant concentration of all the reactants, the effect of added ions on the rates of reaction was investigated by varying the concentration of acetate ion (CH₃COO^–) from  30×10^-3 – 130×10^-3 mol dm^-3 and noting the rates of the reactions. The same was repeated for magnesium ion (Mg²⁺).  For this system, the rates of reaction were found unaffected by the presence of either Mg²⁺ or CH₃COO^–The temperature dependence of rates on this reaction was investigated at 35⁰C, 40⁰C, 50⁰C, 55⁰C and 60⁰C respectively. It was found that increase in temperature increases the rates of reaction. The plot of logk_obs versus the reciprocal of the square of temperature is linear, hence the activation parameters were evaluated.

CHAPTER ONE

1.      INTRODUCTION

 1.0    BACKGROUND OF THE STUDY

       1.1     ELECTRON TRANSFER

Electron transfer (ET) occurs when an electron moves from an atom or a chemical species ( e.g. a molecule) to another atom or chemical species.  Electron transfer is a mechanistic description of the thermodynamic concept of redox, wherein the oxidation states of both reaction partners change.

Numerous biological processes involve electron transfer reactions. These processes include oxygen binding, photosynthesis, respiration, and detoxication. Additionally, the process of energy transfer can be formalized as two-electron exchange (two concurrent electron transfer events in opposite directions) in case of small distances between the transferring molecules.

1.2           CLASSES OF ELECTION TRANSFER

There are several classes of electron transfer, defined by the state of the two redox centers and their connectivity.

1.2.1       Inner sphere electron transfer

In inner sphere electron transfer, the two redox centers are covalently linked during the electron transfer (Burgees, 1978). This bridge can be permanent, in which case the electron transfer event is termed intermolecular electron transfer. More commonly, however, the covalent linkage is transitory, forming just prior to the electron transfer and then disconnecting following the electron transfer event. In such cases, the electron transfer is termed intermolecular electron transfer. A famous example of an inner sphere electron transfer that proceeds by a transitory bridged intermediate is the reduction of [CoCl(NH₃)₅]²⁺ by [Cr(H₂O)₆]²⁺ (Taub and Meyer, 1954). In this case the chloride ligands is the bridging ligands that covalently connects the redox partners.

1.2.2     

 Outer sphere electron transfer