Kinetics and Mechanism of the Reactions of Alkyllithium Reagents With Ketones and Esters in Hydrocarbon Solvents
Al-Aseer, Munther Adil
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https://hdl.handle.net/2142/70215
Description
Title
Kinetics and Mechanism of the Reactions of Alkyllithium Reagents With Ketones and Esters in Hydrocarbon Solvents
Author(s)
Al-Aseer, Munther Adil
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
Date of Ingest
2014-12-15T23:17:53Z
Keyword(s)
Chemistry, Organic
Abstract
The kinetics of the reactions of alkyllithium reagents with ketones and esters in cyclohexane and benzene have been investigated by stopped-flow infrared spectroscopy at 25.0(DEGREES)C. A series of substituted phenyl-sec-butyl ketones (10a-i) and substituted ethyl benzoates (13a-i) along with several aliphatic ketones (14-17) and esters (18,19) were utilized in the study. These compounds were found to form coordination complexes with alkyllithium aggregates. Evidence for this was demonstrated by the appearance of a new carbonyl band in the infrared spectrum of a reacting solution of ester or ketone and alkyllithium reagent immediately after mixing. The new band, which is shifted to lower wave-number relative to the carbonyl band of the carbonyl compound, has been attributed to the formation of a substrate-alkyllithium aggregate complex in rapid equilibrium with the free substrate. Equilibrium constants (K(,c)) for complexation with sec-butyllithium in cyclohexane were determined for several compounds. A trend in the K(,c) values for the substituted phenyl-sec-butyl ketones and ethyl benzoates was observed: the more electron donating the substituent the larger the equilibrium constant of complexation. Further, larger K(,c) values were obtained for the esters, in their reactions with sec-butyllithium, than for the corresponding ketones.
The rate of disappearance of ketones 10a-i and esters 13a-i in the presence of excess sec-butyllithium exhibited good pseudo first order behavior. The dependence of the observed pseudo first order rate constant (k(,obs)) on sec-butyllithium concentration was complex indicating the lack of a simple order with respect to alkyllithium in these reactions. Within each class of carbonyl compounds a substituent effect on the rate data was noted. Electron-withdrawing substituents on the phenyl ring of the ketone or ester led to the common behavior of increasing k(,obs) with rising reagent concentration; whereas, electron-donating substituents brought about a maximum k(,obs) followed by a decrease in k(,obs) at higher lithium reagent concenrations.
A mechanism (Scheme 5) that is consistent with the kinetic and equilibrium data has been proposed in which product is formed by two pathways: decomposition of the ketone/ester-alkyllithium complex and reaction of uncomplexed ketone/ester with monomeric alkyllithium.
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