1H nuclear magnetic resonance studies of solutions of aromatic bases. Part I. Proton exchange in ethanol solutions of pyridines

Abstract

The overall rate of proton exchange in ethanol solutions of pyridine, γ-picoline, and 2,6-lutidine was measured by observation of the methylene proton lineshape as a function of concentration. The process obeys the empirical rate equation (i) where k₁= 2·8 × 10⁹ l mol^–1 s^–1 for pyridine, 4·3 × 10⁸ for γ-picoline, and 0·7 × 10⁸ for 2,6-lutidine and k₂ is approximately constant at 6 × 10⁸ s^–1. The first term refers to the symmetrical exchange reaction (ii). Rate =k₁[BH⁺][B]+k₂[BH⁺] mol l^–1 s^–1(i), BH⁺+ EtOH*+ B ⇌ B + HOEt + H*B⁺(ii)

The second term may reflect exchange catalysed by EtO^–.