Kinetic studies of proton transfer between 2,6-di-t-butylpyridine and its conjugate acid in [2H2]dichloromethane and in methanol

Abstract

Proton transfer from the 2,6-di-t-butylpyridinium ion (as the chloride or bromide) to 2,6-di-t-butylpyridine has been investigated by ¹H n.m.r. line-shape analysis of solutions in a non-polar medium (CD₂Cl₂) and in a polar medium (MeOH). The mechanism in the former solvent depends on dissociation of the contact ion pair. In the presence of water the mechanism involves proton jump via an intervening water molecule rather than an acid dissociation step, although at high water concentrations this latter process becomes important. In methanol as solvent the acid dissociation step is the dominant one.