The rates of quaternization of substituted pyridines with dodecyl bromide were measured in methanol and dimethylformamide(DMF). The effects of Substituents and solvents on the reactivity of pyridines were discussed. The rates of the reaction showed larger values in DMF than in methanol and increased with the electron repelling power of Substituents. The isokinetic relationship was seen between E and ASa except for 4-aminopyridine. The excellent linear relationships, given by the following equations, were observed between log k and PKa "of pyridines except 4-aminopyridine, but the deviations from the Hammett line were also noticed for pyridines substituted with amino, benzoyl, alkexycarbonyl and cyano groups at 4-position. These deviations were considered to be attributed to the localzation of rr-electron on pyridine ring induced by the nuclear nitrogen atom and the 'variation of solvation on the substituents.
log k=0.157 PKa-5.250 (in DMF at 50°C)
log k=0.136 PKa-4.586 (in methanol at 750°C)