Date of Award
Doctor of Philosophy
A general, nonspecialized method for producing superoxide ion in aqueous solution has been developed. The method is based upon photochemical generation of a reducing radical species and its subsequent reaction with dioxygen to produce O(,2)('-). The product is identified as superoxide ion by comparison with the known UV spectrum of O(,2)('-) and by measuring the rate of loss of the photolysis product. Factors affecting the yield of O(,2)('-) are investigated. Optimal working conditions proved to be 5.0 M 2-propanol, 6.3 (mu)M Ph(,2)CO, dioxygen saturated at pH > 11 with irradiation performed using a Hg arc lamp photoreactor. Nearly 400 (mu)M O(,2)('-) is produced in 30 s under these conditions;The reactions of O(,2)('-) with several cobalt(III) complexes and ferricinium ion proceed through an outer sphere electron transfer pathway. Second-order rate constants at 25.0(DEGREES)C are: 31.3, 23.8, and 16.4 M('-1) s('-1) for Co(NH(,3))(,6)('+3), Co(en)(,3)('+3), and Co(trans-1,2-cyclohexanediamine)(,3)('+3), respectively, and 8.6 x 10('6) M('-1) s('-1) for Cp(,2)Fe('+). For the Co(III) reactions, several physical (temperature, pH) and chemical (isotopic labeling of complex and solvent, choice of counter anion, presence of dioxygen) effects were investigated. Some observations, through use of the Marcus correlation, are made on the O(,2)(aq)/O(,2)('-) electron self-exchange rate constant;The stoichiometry and kinetics of the reactions of bis(dimethyl- glyoximato)cobalt(II) complexes with polyhalomethanes are also reported. A two-step mechanism is supported by the data. The first and rate limiting step is halogen atom abstraction by the cobalt complex and formation of a free radical. The existence and reactivity of the latter is demonstrated through the use of the radical scavenging agent 4-hydroxy-2,2,6,6-tetramethylpiperidinooxy (4- HTMPO) in a kinetic competition mode. Numerical integration techniques were used to simulate data with various choices of competitive rate constants, permitting an estimation of the relative rate constants for the reaction of (.)CCl(,3) and 4-HTMPO vs. its reaction;with Co(dmgH)(,2)py in benzene. The ratio was found to be 1.8 (+OR-) 0.1 at 25.0(DEGREES)C; ('1)DOE Report IS-T-1083. This work was performed under Contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Michael Steven McDowell
McDowell, Michael Steven, "Free radical reactions of some transition and organotransition metal complexes " (1983). Retrospective Theses and Dissertations. 8939.