Redox-transfer. Part VI. Determination of Hammett's ρ-constant for the oxidation of cuprous chloride by aromatic sulphonyl chlorides

Abstract

The copper chloride-catalyzed redox-transfer chain addition of styrene to aromatic sulphonyl chlorides which carry substituents with a wide range of Hammett σ-values, has been studied by dilatometry at 110° with acetonitrile as the solvent. When an excess of styrene is used, the rate of the overall addition is governed by the slowest step of the chain propagation, i.e. the oxidation of cuprous chloride by sulphonyl chloride. Hammett's equation is obeyed for this reaction, and gives a ρ-value of 0·565. This is the first time that Hammett's equation has been shown to be valid for the homolytic abstraction of an atom other than hydrogen. The overall addition is first-order in copper chloride up to 5 × 10^–3M, and in sulphonyl chloride up to at least 70% conversion.