Thermodynamics of protonation of 2-ethyl-, 3-ethyl-, 4-benzyl-, 3-ethyl-4-methyl- and 5-ethyl-2-methyl-substituted pyridine-N-oxides in aqueous media

Thermodynamics protonation constants of 2-ethyl-, 3-ethyl-, 4-benzyl-, 3-ethyl-4-methyl-,and 6-ethyl-2-methyl-substituted pyridine-N-oxides in aqueous media have been measured spectrophotometrically in the range 20–60°C. The effects of alkyl and benzyl substituents on base strength are explained in terms of inductive and resonance effects, and the resulting thermodynamic quantities as sums of environmental and internal contributions. The Hammett sigma values of a number of alkyl and benzyl substituted pyridine-N-oxides are also reported.