Volume 7 Issue 3
Use of Linear Free Energy Relationships (LFERs) to Elucidate the Mechanisms of Reaction of a γ-Methyl-β-alkynyl and an ortho-Substituted Aryl Chloroformate Ester
Malcolm J. D’Souza, Jaci A. Knapp, Gabriel A. Fernandez-Bueno and Dennis N. Kevill
1Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901, USA
2Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA
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Abstract
The specific rates of solvolysis of 2-butyn-1-yl-chloroformate (1) and 2-methoxyphenyl chloroformate (2) are studied at 25.0 °C in a series of binary aqueousorganic mixtures. The rates of reaction obtained are then analyzed using the extended Grunwald-Winstein (G-W) equation and the results are compared to previously published G-W analyses for phenyl chloroformate (3), propargyl chloroformate (4), p-methoxyphenyl choroformate (5), and p-nitrophenyl chloroformate (6). For 1, the results indicate that dual side-by-side addition-elimination and ionization pathways are occurring in some highly ionizing solvents due to the presence of the electron-donating γ-methyl group. For 2, the analyses indicate that the dominant mechanism is a bimolecular one where the formation of a tetrahedral intermediate is rate-determining.
Keywords:solvolysis; nucleophilicity; ionizing power; γ-Methyl-β-alkynyl chloroformate; 2-butyn-1-yl-chloroformate; aryl chloroformate; 2-methoxyphenyl chloroformate; Grunwald-Winstein equation; Linear Free Energy Relationships (LFERs)