Dediazoniations of Arene Diazonium Ions in Homogeneous Solution. Part VI: Solvolyses in 2,2,2-trifluoroethanol/water mixtures and exclusion of a potential aryne mechanism

The rates and products of dediazoniation of benzenediazonium tetrafluoroborate in 2,2,2‐trifluoroethanol (TFE)/water mixtures has been determined. The results are not consistent with a mechanism in which TFE and water enter the rate‐determining part of the reaction as nucleophiles. The influence of the solvent composition on product ratios and rates is explained as a solvent effect, the formation of a (solvated) aryl cation being the rate‐determining part of the reaction. The magnitude of the preexponential factor of the Arrhenius equation is consistent with this interpretation. Since the solvolysis of p ‐chlorobenzenediazonium tetrafluoroborate in TFE yields no detectable m‐products, an aryne‐like mechanism is excluded.