Quaternary Nitrogen Heterocycles. II. Kinetics of Reversible Pseudobase Formation from N-Methyl Heterocyclic Cations

Abstract

The kinetics of the formation and decomposition of the pseudobases from the 2-methyl-4-nitroisoquinolinium, 10-methylacridinium, and 10-methyl-9-phenylacridinium ions have been studied. The pH–rate profiles of these reactions indicate that for each of these ions, pseudobase formation may kinetically involve either attack of a water molecule or of hydroxide ion on the heterocyclic cation depending upon the pH of the reaction. Pseudobase decomposition to the cation may occur through either the neutral or protonated pseudobase species or their kinetic equivalents. The temperature dependences of the equilibrium and kinetics are reported for each ion, and deuterium isotope effects for the reactions of the 2-methyl-4-nitroisoquinolinium ion have been measured. Possible mechanisms for the reactions are discussed on the basis of the observed activation parameters and isotope effects and are compared with related reactions.