Homogeneous and heterogeneous catalytic systems for the oxidation of organic sulfides

Leslie Villalobos, Purdue University

Abstract

The catalytic activity of diruthenium(II,III) paddlewheel compounds have been studied for the oxidation of organic sulfides with hydrogen peroxide (H2O2) and tert-butyl hydroperoxide (TBHP) as terminal oxidants. Investigation on ruthenium complexes with amidate ligands and carboxylate ligands such as, Ru2(NHOCC(CH3)2)4Cl, Ru2(NHOCCH2CH3)4Cl and Ru 2(OAc)4Cl showed high reactivity and good to excellent selectivity towards oxidation of organic sulfides. Using excess oxidant and CH3CN as the solvent, organic sulfides such as methyl phenyl sulfide (MPS) and diphenyl sulfide (PPS) were oxidized using 1 mol% of the catalytic species. Fast conversion was achieved when the reactions were carried out under solvent-free conditions, and the major oxidation product was the sulfoxide. Electronic structures of the title compounds were studied with DFT calculations to gain an understanding of the activation of peroxy reagents. Many immobilized catalysts that have been developed prove to be more efficient than the non-immobilized specie. Ru2(OAc)4Cl was successfully immobilized into MCM-41 by ligand exchange with a surface grafted tether forming MCM-41-(CH2 )2-Ru2(OAc)4Cl. After the catalytic specie was immobilized and characterized; the next step was to determine the material activity in the oxidation of organic sulfides and to compare the rates of conversion between the homogeneous and heterogeneous reactions. Besides, the recyclability of the material was tested. Best results were achieved using excess of TBHP as the oxidant and CH3CN as the solvent with 1 mol% of the catalytic species at 55º C. In order to develop a more economical procedure, these ruthenium catalysts were replaced by simple iron salts such as iron(III) chloride and iron(III) bromide. Organic sulfide oxygenation by H2O2 was effectively accomplished at room temperature in the presence of catalytic amounts of the mentioned iron salts. The effect of different solvents on the rate of conversion and selectivity was also examined and the system showed good reactivity toward sulfide oxidation in all solvents studied. The iron salts used in this study were able to convert the sulfides to the sulfoxide in acetonitrile with yields between 46-91%. The reaction can also take place under organic-aqueous biphasic conditions affording 100% of the sulfoxide.

Degree

Ph.D.

Advisors

Ren, Purdue University.

Subject Area

Chemistry|Inorganic chemistry

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