Kinetic and equilibrium acid–base properties of strong naphthalene-diamine bases

Abstract

The kinetic and equilibrium acid-base properties of two derivatives of the strong base 1,8-bis(dimethylamino)naphthalene (1), pK 12.1, have been investigated. When the nitrogen atoms are bridged as in 2,3,6,7-tetrahydronaphthaleno[1,8-hi][1,4,8]oxadiazecine (2), pK 12.9, the basicity is increased. For 1,8-dimorpholinonaphthalene (3), pK 7.49, the basicity is much lower than for (1) but still four pK units higher than for N-phenylmorpholine. The rate coefficients for proton transfers from the protonated amines (1) and (2) to hydroxide ion in 30%(v/v) Me₂SO–H₂O have values of 6.1 × 10⁵ and 6.2 × 10³ dm³ mol^–1 s^–1 respectively and for (3) in aqueous solution proton transfer from the protonated amine to phosphate dianion occurs with a rate coefficient of 1.2 × 10³ dm³ mol^–1 s^–1. The low rates and high basicities are due to stabilisation of the protonated amines by strong intramolecular hydrogen bonds.