Study on the photolysis and thermolysis of alkyl aryl sulfoxides

Guo, Yushen
Major Professor
William S. Jenks
Committee Member
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After a brief deliberation of the research objective and justification, Chapter 1 is a general literature review of sulfoxide photochemistry. The following four chapters focus on photolysis and thermolysis studies of acyclic sulfoxides employing various structures;The photochemistry of aryl benzyl sulfoxides has been studied in extensive detail as a prototype of [alpha]-cleavage. The initial event is homolytic cleavage to form a singlet arylsulfinyl/benzyl radical pair which partitions between reversion to starting material with at least partial racemization and closure to form a sulfenic ester. This is the first well characterized sulfenic ester intermediate from the photolysis of acyclic sulfoxides. The assignment of the singlet multiplicity is based on solvent cage effects and product distribution. Secondary photolysis of the sulfenic ester leads exclusively to S-O homolysis, yielding the arenethiyl/alkoxyl radical pair from which various isolated products are derived. The photochemistry of a series of alkyl aryl sulfoxides is also described. The quantum yield for conversion depends on the structure or the reactivity of the alkyl radical, according to the following order: benzyl > tertiary alkyl > secondary alkyl > primary alkyl > (di-)aryl. The high racemization efficiency of some aryl primary alkyl sulfoxides suggests the possible existence of another non-radical pathway for the photoracemization process. Product analysis does not support any hydrogen abstraction pathways. The arylsulfinyl radicals are directly observed by nanosecond laser flash photolysis technique. Other mechanistic observations, including solid state photolysis, are also discussed;A comparation of photochemical alkene formation is made to thermal alkene generation. The mechanism of the high temperature thermolyses shows increasing radical character, along with the classical concerted cis-elimination mechanism, as indicated by the presence of alkane products and higher activation parameters. A pulsed stirred-flow reactor was successfully used to study the kinetics of certain less labile sulfoxides. The direct GC injector pyrolysis method has proven to be a simple and fast approach to determine the relative activation parameters of thermolysis products with good precision.