The Kinetics and Mechanism of Complex Redox Reactions in Aqueous Solution: The Tools of the Trade

Redox reactions of simple inorganic species exhibit an amazingly rich variety of complex kinetic phenomena. Typically, these reactions are interpreted on the basis of multistep kinetic models which postulate the formation and subsequent fast reactions of reactive intermediates. The main purpose of this chapter is to demonstrate the challenges associated with mechanistic studies on complex redox reactions, and to offer selected examples how the complexities can be handled with currently available experimental and computational methods. Clear arguments are presented to demonstrate that the stoichiometries of these reactions are kinetically controlled. It is shown that in order to understand the intimate details of these systems, the stoichiometry as a function of reaction time, the final stoichiometry and the kinetic properties need to be studied under as broad experimental conditions as possible. Furthermore, thorough characterization of the reactive intermediates is the key to in-depth understanding of the mechanism. The importance of photoinitiation and kinetic coupling between photochemical and thermally activated reaction steps is also demonstrated in several systems. The survey of the literature results confirms that simultaneous and critical evaluation of all available experimental results is essential to validate the mechanistic conclusions. Finally, it is shown that adapting the methodology of homogeneous reaction kinetics for studying nonhomogeneous physicochemical processes leads to unique kinetic information regarding the kinetics of adsorption and desorption processes.