Kinetics and Mechanism of the Reaction of 4,4'-Dimethoxythio Benzophenone With Grignard Reagents
Fradenburgh, Sharon Ann
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https://hdl.handle.net/2142/70243
Description
Title
Kinetics and Mechanism of the Reaction of 4,4'-Dimethoxythio Benzophenone With Grignard Reagents
Author(s)
Fradenburgh, Sharon Ann
Issue Date
1983
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Organic
Abstract
The mechanism of the reaction of 4,4'-dimethoxythiobenzophenone with Grignard reagents was investigated kinetically by stopped-flow spectroscopy. The reaction of this thioketone with methylmagnesium bromide in ether at 25.0(DEGREES)C was found to be first order in thioketone and first order in Grignard, with a second-order rate constant of 0.047 (+OR-) 0.002 s('-1)M('-1). The mechanism proposed to account for the products of the reaction involves slow thiophilic addition of Grignard to thioketone, followed by fast carbophilic addition of the intermediate thus formed to a second molecule of thioketone. The resulting dimeric intermediate produces the sulfide corresponding to thiophilic addition and regenerates thioketone upon aqueous quench at short reaction times. It proceeds to stable dimeric products at very long reaction times. The kinetics of the reaction of 4,4'-dimethoxythiobenzophenone with ethylmagnesium bromide in tetrahydrofuran at 50.0(DEGREES)C are complex, showing an initial fast reaction, followed by one or more successively slower reactions, depending on the wavelength of observation. The reaction proceeds cleanly to the sulfide resulting from thiophilic addition within five minutes. Further investigation is required before a detailed mechanism can be proposed for this reaction.
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