Rates of proton transfer from protonated 1,8-bis(dimethylamino)- and 1,8-bis(diethylamino)-naphthalene to hydroxide ion in 20% and 30%(v/v) dimethyl sulphoxide–water

Abstract

The conjugate acids of 1,8-bis(dimethylamino) naphthalene and 1,8-bis(diethylamino) naphthalene are intramolecularly hydrogen-bonded, and proton transfers to hydroxide ion in 30%(v/v) dimethyl sulphoxide–water occur slowly, with rate coefficients (k_OH–) 6.1 ± 10⁵ and 1.6 ± 10⁴ I mol^–1 s^–1, respectively. Substitution of ethyl groups for methyl groups in 1,8-bis(dimethylamino)naphthalene has a larger effect on the rate of proton transfer than on the equilibrium constant, and this unusual observation is considered in terms of a two-step mechanism for proton removal from the protonated amines.