Green synthesis in microemulsions with cobalt macrocyclic catalysts

Date of Completion

January 2005


Chemistry, Analytical




In this thesis, the use of microemulsions as alternative solvents for traditional organic synthesis was explored. Microemulsions are mixtures of oil, water and surfactant and are the media of choice for mediated and direct electrochemical synthesis. The unique capacity of microemulsions to solubilize both polar and non-polar substrates is the focus of their use as reaction media. In the first part, vitamin B12 mediated electrochemical reduction of methylene chloride in presence of styrene was explored in dimethyl formamide (DMF) and in microemulsions. The main product of interest is the three membered ring of cyclopropyl benzene. Most known methods of cyclopropanation utilize more than stoichiometric amounts of reductant and disposal of spent reagent is an environmental problem. The novelty of our reaction is the complete elimination of reducing agents, and use of nonstoichiometric amounts of the catalyst vitamin B12. The second part of the thesis focuses around the building of protein reconstituted films that are stable and electroactive in microemulsions. Covalently-linked films of Cobalt protoporphyrin IX-reconstituted Myoglobin (CoMb) and poly-L-lysine (PLL) were built on the surfaces of oxidized carbon cloth electrodes for evaluation of catalytic applications. These films were characterized by UV-Vis spectroscopy and voltammetry in a bicontinuous cetyltrimethylammonium bromide (CTAB) microemulsion. ^ Voltammetry of the films gave well defined, quasi-reversible Co III/CoII and CII/CoI peaks in the microemulsion. The CoMb-PLL films catalyzed debromination of ethylene dibromide (EDB) and trans-1,2-dibromocyclohexane (DBCH) in the microemulsion. Finally, enantioselective ring opening of 1,2-epoxycyclopentane by vitamin B12 was carried out in different microemulsions. Vitamin B12 catalyzed ring opening of 1,2-epoxycyclopentane in bicontinuous microemulsion of sodiumdodecylsulfate to selectively form the (R)-cyclopentene-1-ol with 52% enantiomeric excess (ee) and yield of 58%. The influences of structure, composition and pH of water phase of microemulsions on enantioselectivity of the reaction were explored. In microemulsions, the ee of the reaction was influenced by the water content of the microemulsions, the availability and intermixing of the catalyst with substrate. ^