Chemistry and Biochemistry
Bayer School of Natural and Environmental Sciences
Atom Transfer Radical Addition, Copper Catalysts, Free-Radical Diazo Initiators, Kinetics, Reducing Agents
The first part of this dissertation focuses on the kinetic aspects of atom transfer radical addition (ATRA) in the presence of reducing agents. The rate of alkene consumption was found to be dependent on the initial concentration of the radical initiator and its decomposition and termination rate constants but not on the concentrations of CuI and CuII, which was contrary to the rate law for copper-catalyzed ATRA in the absence of a reducing agent. Kinetic experiments showed that the observed rate of ATRA (kobs) was indeed not dependent on the concentration of the catalyst, which supported the newly derived rate law. However, product selectivity was highly dependent on the nature of the catalyst. The activation (ka,AIBN) and deactivation (kd,AIBN) rate constants of various CuII/AIBN systems were determined through a combination of experimental and theoretical methods and were found to control the overall concentrations of CuI and CuII at equilibrium.
The effect of the catalyst, alkyl halide, and free radical initiator concentrations on the percent conversion and yield of monoadduct were also investigated. Lower catalyst loadings in ATRA reactions involving reactive monomers led to a decrease in monoadduct yield due to competing polymerization reactions. Low-temperature ATRA reactions were found to significantly increase the formation of the monoadduct as a result of the lowering of the rate constant of propagation (kp). Reactions of less active halides were more affected by increased alkyl halide concentrations than that of the more active alkyl halides. Higher free radical initiator concentration led to an increase in AIBN-initiated polymer formation.
The second part explores the role of thermodynamic factors on the product selectivity of atom transfer radical cyclization (ATRC). Various derivatives of alkenyl bromoacetate and trichloroacetate were synthesized and characterized by 1H NMR spectroscopy. Theoretical calculation of the relative energies of the s-trans and s-cis conformers revealed that the presence of bulky substituents on the carbon atom adjacent to the acetate moiety stabilizes the s-cis conformation and, thus, promotes cyclization. This was experimentally confirmed in the ATRC reactions of the synthesized alkenyl haloacetates in which the addition of bulky groups increased the yields of cyclic products.
Balili, M. (2010). Kinetic and Thermodynamic Studies of Copper-Catalyzed Atom Transfer Radical Processes in the Presence of Free-Radical Diazo Initiators as Reducing Agents (Doctoral dissertation, Duquesne University). Retrieved from https://dsc.duq.edu/etd/261