Dynamics of Mediated Electrochemical Synthesis in Microemulsions

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ABSTRACT CTS-9632391 The goal of this project is to develop a fundamental understanding of how surface dynamics on electrodes and kinetics in microemulsions influence control of reactivity in mediated electrochemical syntheses. Electrochemical studies are used to relate surfactant and reactant adsorption-desorption dynamics on electrode surf aces to catalytic reaction rates. The mediated reactions include carbon-carbon coupling, cyclizations, and olefin production. Catalytic efficiencies of mediators in the bulk fluid using bare carbon electrodes will be compared with those of new catalytic electrodes designed specifically to achieve high reaction rates in microemulsions. Macrocyclic metal complexes that catalyze reactions by efficient inner sphere pathways, such as vitamin B12 and Cobalt-, iron-, and nickel-porphyrins, are used as mediators. Layer-by-layer electrode coating strategies based on polymeric silicon-oxygen-carbon linkages to carbon electrodes are compared with a previously developed polymer deposition method. Electroanalytical methods are used to compare reaction rates in microemulsions and homogeneous organic solvents and catalytic electrodes. Synthetic electrolyses in a stirred batch electrochemical reactor with product analysis are used to assess the practical utility of the systems, and to optimize yields and reactant conversion rates. Compositions of microemulsions and properties of catalytic coatings are tuned for best reaction rates and yields for key reactions. Surface dynamics of reactants and surfactants on electrodes are measured by time-resolved flow voltammetry on bare and catalytic electrodes. Methods and theory developed earlier are employed. Molecular interactions between co-adsorbates will be assessed via Frumkin interaction parameters obtained from wave voltammetry. As possible limiting factors for the rates of mediated reactions, reactant and surfactant exit and entry rates are estimated for the new catalytic films using electroactive probes. Correlations between rates of all surface dynamic events and rates of mediated synthetic reactions are sought. The objective of this work is to provide fundamental guidance for the future design of efficient mediated electrochemical synthetic processes in relatively inexpensive, low toxicity, water-based fluid media. Mediated electrochemical addition reactions are major targets because these atom-economical processes can be utilized to prepare chemicals of many classes, including lactones, pheromones, prostaglandins, C-glycosides, optically active olefins and alcohols, and cyclic molecules. New catalytic surfaces design specifically for microemulsions combined with kinetic control by fluid composition may provide a basis for future cost-effective, environmentally benign processes for the synthesis of high value chemicals.