Reactions of N-heteroaromatic bases with nitrous acid. Part 9. Kinetics of the nitrosation of 1-methyl-3- and 1-methyl-4-methylaminopyridinium perchlorate in aqueous perchloric acid and 13C nuclear magnetic resonance spectra of 1-methyl-4-alkylamino-substituted pyridinium ions

Abstract

The nitrosation of 1-methyl-3-methylaminopyridinium perchiorate in 0.001–0.50M-perchloric acid and of 1-methyl-4-methylaminopyridinium perchlorate in 0.10–4.00M-perchloric acid is of first order in both the amine salt and nitrous acid. The rate coefficients increase with an increase in the concentration of perchloric acid and sodium perchlorate. At constant ionic strength the rate coefficients show a rectilinear dependence on [H⁺] and on the h₀ parameter of the medium. The nonequivalence of the two α- and the two β-carbons observed in the ¹³C n.m.r. spectra of 1-methyl-4-methylamino- and 1-methyl-4-ethylamino-pyridinium perchiorate, but not in that of 1-methyl-4-dimethylaminopyridinium perchiorate, and the values of the energy barrier of rotation determined for the former amines indicate that the exocyclic carbon–nitrogen bond has substantial double-bond character. The present results are in accord with the conclusion that the nitrosation of the protonated β-aminopyridines involves an interaction between the nitrosating species and the exocyclic amino group, whilst the nitrosation of the protonated γ-aminopyridines involves an association of the nitrosating species with the π-electrons of the pyridinium nucleus.