Kinetics of reactions in heterocycles. Part XIII. Substituted N-methylpyridinium and N-methylquinolinium salts with piperidine in water and in ethanol

Abstract

Kinetics of the displacement reactions of some halogeno-N-methylpyridinium and -N-methylquinolinium salts towards half-neutralised piperidine in water, and unneutralised piperidine in ethanol have been determined. These revealed, for reactions in water, smaller differences in reactivity between 2- and 4-isomers than was observed with hydroxide ions. Energies of activation for the reactions with piperidine were 3.7–5.4 kcal mol^–1 lower and log A values were lower by 2.9–3.4 and 0.7–1.9 units for pyridinium salts with the substituent at the 2- and 4-position respectively. Displacement reactions with piperidine in ethanol were found to occur 8.0–16.75 times faster than in water. Quaternisation of 4-chloroquinoline by methylation increased its reactivity towards piperidine in ethanol at 100° by 2 × 10⁸ fold.