Sandmeyer reactions. Part 2. Estimation of absolute rate constants for some hydrogen-transfer reactions and for the transfer of water ligands on CuII to aryl radicals by use of a Pschorr radical clock

Abstract

The rate constant for the homolytic Pschorr cyclization of 2-benzoylphenyl radical has been estimated for ambient temperature (20 °C) by competing the cyclization against intermolecular hydrogen-abstractions from alcohols and assuming the latter to occur at rates equal to those measured by Schuler for 4-carboxyphenyl radical. The cyclization was then used as a radical clock for estimating rate constants for other reductions of aryl radicals and for the transfer of water ligands to aryl radicals from Cu^II. It is found that sulfate ion inhibits the transfer of water and an explanatory mechanism is proposed.