Malcolm J D'Souza1, Dennis N Kevill2. 1. Department of Chemistry, Wesley College, 120 N. State Street, Dover, DE 19901-3875, USA. 2. Department of Chemistry & Biochemistry, Northern Illinois University, DeKalb, IL 60115-2862, USA.
Abstract
Chloroformates are important laboratory and industrial chemicals with almost one hundred listed in the catalogs of leading suppliers. They are, for example, of prime importance as protecting groups in peptide synthesis. In some instances, the more stable fluoroformate is preferred. In recent years, the specific rates of solvolysis (k) for chloroformates and fluoroformates in solvents of widely ranging nucleophilicity and ionizing power have been studied. Analysis of these rates using the extended (two-term) Grunwald-Winstein equation has led to important information concerning reaction mechanism. Also assisting in this effort have been studies of kinetic solvent isotope effects (KSIE), of leaving group effects (especially kF/kCl ratios), and of entropies of activation from studies of specific rate variations with temperature. For solvolyses of chloroformate esters, two mechanisms (addition-elimination and ionization) are commonly encountered. For solvolyses of fluoroformates, mainly because of a strong C-F bond, the ionization pathway is rare and the addition-elimination pathway is in most situations the one encountered.
ical">Chloroformates are importaical">nt laboratory aical">nd iical">ndustrial chemicals with almost oical">ne huical">ndred listed iical">n the catalogs of leadiical">ng suppliers. They are, for example, of prime importaical">nce as protectiical">ng groups iical">n peptide sypan class="Chemical">ical">nthesis. Iical">n some iical">nstaical">nces, the more stable ical">n class="Chemical">fluoroformate is preferred. In recent years, the specific rates of solvolysis (k) for chloroformates and fluoroformates in solvents of widely ranging nucleophilicity and ionizing power have been studied. Analysis of these rates using the extended (two-term) Grunwald-Winstein equation has led to important information concerning reaction mechanism. Also assisting in this effort have been studies of kinetic solvent isotope effects (KSIE), of leaving group effects (especially kF/kCl ratios), and of entropies of activation from studies of specific rate variations with temperature. For solvolyses of chloroformate esters, two mechanisms (addition-elimination and ionization) are commonly encountered. For solvolyses of fluoroformates, mainly because of a strong C-F bond, the ionization pathway is rare and the addition-elimination pathway is in most situations the one encountered.
Authors: Malcolm J D'Souza; Aaron F Givens; Peter A Lorchak; Abigail E Greenwood; Stacey L Gottschall; Shannon E Carter; Dennis N Kevill Journal: Int J Mol Sci Date: 2013-04-02 Impact factor: 5.923
Authors: Malcolm J D'Souza; Richard J Kashmar; Kent Hurst; Frank Fiedler; Catherine E Gross; Jasbir K Deol; Alora Wilson Journal: Contemp Issues Educ Res (Littleton) Date: 2015 Third Quarter