Photochemical and computational study of sulfoxides, sulfenic esters, and sulfinyl radicals

Abstract

<p>Despite a fairly long history of research, sulfoxide photochemistry has not been extensively developed. This is particularly true in terms of structural effects on the observed sulfoxide photochemistry. Because of this, our group has embarked on an extensive study to gain a better understanding of sulfoxide photochemistry and the effects of structure on this photochemistry. The intention of this research is to obtain knowledge of sulfoxide photochemistry that can be used as a predictive tool in the photolysis of other sulfoxide systems. Sulfoxide photochemistry can be divided into four general reaction types. These include alpha-cleavage, hydrogen abstraction, stereomutation, and deoxygenation. All of these reactions will be discussed to varying extents in this dissertation;Photolysis of dibenzothiophene sulfoxide results in the formation of dibenzothiophene and oxidized solvent. Though quantum yields are low, chemical yields of the sulfide are quite high. Yields of the oxidized solvents can also be high. Typical products are phenol from benzene, cyclohexanol, and cyclohexene from cyclohexane and 2-cyclohexenol and epoxycyclohexane from cyclohexene. A number of experiments designed to elucidate the mechanism of the hydroxylation were carried out, including measurements of quantum yields as a function of concentration, solvent, quenchers, and excitation wavelength. These data are inconsistent with a mechanism involving a sulfoxide dimer, which also does not properly account for the solvent oxidations. It is suggested that the active oxidizing agent may be atomic oxygen O(3P) or a closely related noncovalent complex, based on the nature of the oxidation chemistry, comparison to known rate constants for O(3P) reactivity, and the quantum yield data;A computational study on the thermochemistry of several simple sulfenic acids (RSOH) and esters (RSOR') is reported. The sulfinyl radical was study computationally and the ground and excited electronic states using ab-initio and density functional methods. The coupling reaction of sulfinyl radicals is also investigated. The reaction of the methylthiyl radical with oxygen was also investigated us the G2 method.</p>