1,8-Dimorpholinonaphthalene: proton transfer reactions

Abstract

1,8-Dimorpholinonaphthalene is found to have an unusually high basicity [pK_a(BH⁺)= 7.51 ± 0.01] and rate constants for downhill proton transfer from its conjugate acid which are substantially below (by factors of 10⁵–10⁷) the encounter-controlled limit. This is taken to indicate that this base, in forming its conjugate acid, receives a proton into a strong intramolecular hydrogen bond, thus relieving a considerable amount of steric strain. The isotope effect on deprotonation of the conjugate acid by hydroxide ion, as well as the appearance of the Brönsted plot for this reaction, are consistent with a two-step mechanism for proton transfer out of the intramolecular hydrogen bond.