Mechanistic studies of the solvolysis of alkanesulfonyl and arenesulfonyl halides

There have been several studies on the solvolysis mechanisms for alkanesulfonyl chlorides (RSO2Cl) and arenesulfonyl chlorides (ArSO2Cl). The earlier of these studies were reviewed a little over thirty years ago by Gordon, Maskill and Ruasse (Chem. Soc. Rev. 1989, 18, 123-151) in a contribution entitled "Sulfonyl Transfer Reactions". The present review will emphasize more recent contributions and, in particular, the application of the extended Grunwald-Winstein equation and kinetic solvent isotope effects to the solvolysis reactions. There is also an appreciable number of reports concerning the corresponding anhydrides with the chloride leaving group replaced by the appropriate sulfonate leaving group, concerning sulfamoyl chlorides (ZZ'NSO2Cl) with Z and Z' being alkyl or aryl and concerning the solvolysis of chlorosulfate esters (alkoxy- or aryloxysulfonyl chlorides), with the structures ROSO2Cl or ArOSO2Cl. The solvolyses of these additional types of sulfur(VI) substrates will be the topics of a future review.

Calculated third order rate constants for interpreting the mechanisms of hydrolyses of chloroformates, carboxylic Acid halides, sulfonyl chlorides and phosphorochloridates

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 (S_N1) to concerted S_N2 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 S_N1-S_N2 spectrum and an S_N2-S_N3 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 S_N2-S_N3 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 S_N2-S_N3 to S_N1-S_N2 (e.g., for benzoyl chloride).