KINETIC SOLVENT ISOTOPE EFFECTS AND ACTIVATION PARAMETERS FOR THE INTRAMOLECULAR ADDITION-ELIMINATION BETWEEN AMINO AND AMIDE GROUPS IN 1-AMINO-8-TRIFLUOROACETYLNAPHTHALENE UNDER ACIDIC CONDITIONS

Rates of the reaction of 1-amino-8-trifluoroacetylaminonaphthalene to 2-trifluoromethylperimidine in the presence of acid have been measured in 70% (v/v) Me2SO-H2O over a range of temperatures and in 70% (v/v) Me2SO-D2O. The dependence of the first-order rate coefficient on hydro nium ion concentration has been fitted to the expression k = (k0H + k( H)[H3O+])/(1 + K(H)[H3O+]) in which the terms k0H and k(H) correspond respectively to spontaneous and hydronium ion catalysed reactions of t he neutral form of 1-amino-8-trifluoroacetylaminonaphthalene and K(H) is the equilibrium constant between 1-amino-8-trifluoroacetylaminonaph thalene and its protonated form which is unreactive. Solvent isotope e ffects and thermodynamic parameters for the individual terms in the ra te expression are explained by a mechanism in which 1-amino-8-trifluor oacetyl-aminonaphthalene reacts by intramolecular addition of the amin o group to the amide carbonyl to give a zwitterionic tetrahedral inter mediate which undergoes rate-limiting protonation by hydronium ion at the diffusion-limited rate and undergoes a rate-limiting proton switch with participation by water. In particular the kinetic solvent isotop e effect on the hydronium ion catalysed reaction is low (k(H)/k(D) 1.4 1) as expected for a diffusion-controlled reaction. The standard entro py change for the intramolecular addition is unfavourable (DELTAS-degr ees - 81 J K-1 mol-1) and the entropy of activation for the solvent-me diated proton switch is also large and negative (DELTAS(double dagger) - 61 J K-1 mol-1).