Substituent effects on the reactions of aromatic triflones with para-X-anilines in methanol: Low intrinsic reactivity and transition state imbalances

A kinetic study is reported for SNAr reactions of 2,4,6-tris(trifluoromethanesulfonyl) anisole 1a with a series of para-X-substituted anilines 2a–e in a methanol solution at various temperatures. The substituent effects on free energy (Δ≠G), enthalpy (Δ≠H), and entropy (Δ≠S) of activation are examined. Aniline addition to triflone 1a is characterized by a βX=0.57, αZ=0.31, and an imbalance of I = αZ–βX=−0.26. The imbalance shows that resonance development lags behind CN bond formation at the transition state. Interestingly, analysis of the results in terms of Marcus theory reveals that these SNAr are associated with some extremely low intrinsic reactivity (log ko=−1.25& © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 255–262, 2011