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

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 CuII. It is found that sulfate ion inhibits the transfer of water and an explanatory mechanism is proposed.