Temperature-jump study of proton transfer from protonated 1,8-bis-(dialkylamino)naphthalenes to hydroxide ion in water and aqueous dioxan

Abstract

The rate coefficients for proton transfer from the protonated forms of 1,8-bis(dimethylamino)-(I) and 1,8-bis-(diethylamino)-naphthalene (II) to hydroxide ion have been determined using the temperature-jump technique. For (I) in aqueous solution, the rate is five orders of magnitude below the diffusion limited rate expected for thermodynamically favourable proton transfer from a nitrogen acid. In 20% dioxan–water (v/v), the rate for (II) is ca. 10² times lower than for (I). Proton transfers involving (I) and (II) occur slowly largely because of a strong intramolecular hydrogen bond in the protonated amines. Steric strain in the transition states may also contribute and is partly responsible for the large rate difference observed for (I) and (II).