Kinetics and Mechanism of the Reaction of 4,4'-Dimethoxythio Benzophenone With Grignard Reagents

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Fradenburgh, Sharon Ann

• Chemistry, Organic

Identifier

(UMI)AAI8409924

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/70243