title: LFER Studies Evaluating Solvent Effects on an α-Chloro-and two β,β,β-Trichloro-Ethyl Chloroformate Esters.
abstract: To provide insight and to identify the occurrence of mechanistic changes in relation to variance in solvent-type, the solvent effects on the rates of solvolysis of three substrates, 2,2,2-trichloro-1,1-dimethylethyl chloroformate, 2,2,2-trichloroethyl chloroformate, and 1-chloroethyl chloroformate, are analyzed using linear free energy relationships (LFERs) such as the extended Grunwald-Winstein equation, and a similarity-based LFER model approach that is based on the solvolysis of phenyl chloroformate. At 25.0 °C, in four common solvents, the α-chloroethyl chloroformate was found to react considerably faster than the two β,β,β-trichloro-substituted analogs. This immense rate enhancement can be directly related to the proximity of the electron-withdrawing α-chlorine atom to the carbonyl carbon reaction center. In the thirteen solvents studied, 1-chloroethyl chloroformate was found to strictly follow a carbonyl addition process, with the addition-step being rate-determining. For the two β,β,β-trichloro-substrates, in aqueous mixtures that are very rich in a fluoroalcohol component, there is compelling evidence for the occurrence of side-by-side addition-elimination and ionization mechanisms, with the ionization pathway being predominant. The presence of the two methyl groups on the α-carbon of 2,2,2-trichloro-1,1-dimethylethyl chloroformate has additive steric and stereoelectronic implications, causing its rate of reaction to be significantly slower than that of 2,2,2-trichloroethyl chloroformate.
authors.affiliation: Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA.
authors.forename: Malcolm J
authors.initials: MJ
authors.lastname: D'Souza
authors.affiliation: Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA.
authors.forename: Brandon
authors.initials: B
authors.lastname: Sandosky
authors.affiliation: Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA.
authors.forename: Gabriel A
authors.initials: GA
authors.lastname: Fernandez-Bueno
authors.affiliation: Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: McAneny
authors.affiliation: Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA.
authors.forename: Dennis N
authors.initials: DN
authors.lastname: Kevill
keywords: 1-Chloroethyl Chloroformate; 2,2,2-Trichloro-1,1-Dimethylethyl Chloroformate; 2,2,2-Trichloroethyl Chloroformate; Addition-Elimination; Grunwald-Winstein Equation; Ionization; Linear Free Energy Relationships (LFERs); Phenyl Chloroformate; Solvolysis