title: Calculated third order rate constants for interpreting the mechanisms of hydrolyses of chloroformates, carboxylic Acid halides, sulfonyl chlorides and phosphorochloridates.
abstract: Hydrolyses of acid derivatives (e.g., carboxylic acid chlorides and fluorides, fluoro- and chloroformates, sulfonyl chlorides, phosphorochloridates, anhydrides) exhibit pseudo-first order kinetics. Reaction mechanisms vary from those involving a cationic intermediate (SN1) to concerted SN2 processes, and further to third order reactions, in which one solvent molecule acts as the attacking nucleophile and a second molecule acts as a general base catalyst. A unified framework is discussed, in which there are two reaction channels-an SN1-SN2 spectrum and an SN2-SN3 spectrum. Third order rate constants (k3) are calculated for solvolytic reactions in a wide range of compositions of acetone-water mixtures, and are shown to be either approximately constant or correlated with the Grunwald-Winstein Y parameter. These data and kinetic solvent isotope effects, provide the experimental evidence for the SN2-SN3 spectrum (e.g., for chloro- and fluoroformates, chloroacetyl chloride, p-nitrobenzoyl p-toluenesulfonate, sulfonyl chlorides). Deviations from linearity lead to U- or V-shaped plots, which assist in the identification of the point at which the reaction channel changes from SN2-SN3 to SN1-SN2 (e.g., for benzoyl chloride).
authors.affiliation: Chemistry Unit, Grove Building, School of Medicine, Swansea University, Swansea SA2 8PP, Wales, UK. t.w.bentley@swansea.ac.uk.
authors.forename: T William
authors.initials: TW
authors.lastname: Bentley
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D002712:Chlorides / Q000737:chemistry*; D005459:Fluorides / Q000737:chemistry; D005561:Formates / Q000737:chemistry; D054879:Halogenation; D006868:Hydrolysis; D007700:Kinetics; D012997:Solvents / Q000737:chemistry; D013441:Sulfinic Acids / Q000737:chemistry*
chemical_list: D002264:Carboxylic Acids; D002712:Chlorides; D005561:Formates; D012997:Solvents; D013441:Sulfinic Acids; C044255:sulfonyl chloride; D005459:Fluorides
keywords: acid chlorides; reaction mechanisms; solvent effects; solvolysis; substituent effects