Heterolytic water activation pathway

Kinetics have been measured for the dediazoniation reactions of 2- and 3-methyl-benzenediazonium cations in water and in aqueous methanol. The results are consistent with a heterolytic mechanism involving rate-determining formation of reactive aryl cations which show little discrimination for nucleophiles present. Results for the dediazoniation of 4-nitrobenzenediazonium ions in aqueous acid catalysed by Cu(II) chloride are also consistent with a heterolytic pathway at low acidity and with conditions designed to avoid the formation of Cu(I) the reaction may yield chloroarenes in high yield. Activation parameters have been reported for the decomposition of some arenediazonium tetrafluoroborates in polar solvents. The results are generally consistent with heterolysis, although in ethanol there is competition from a radical mechanism, with characteristically different activation parameters, which leads to hydrodediazoniation f... 

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