Kinetics and mechanism of the nucleophilic substitution reactions of 2-chloro-1-methylpyridinium iodide with primary and secondary amines

Rate constants for the S(N)2Ar reactions of 2-chloro-1-methylpyridinium iod ide with MeNH2, EtNH2, PrNH2, BuNH2, Me2NH and Et2NH in water, at 1 mol dm( -3) constant ionic strength and 25 degreesC have been determined. The obser ved rare of reaction is first order with respect to amine as well as the py ridinium iodide i.e., the overall reaction is second order. The relative re activity of the amines towards the reactions is Me2NH >> MeNH2 > EtNH2 > Bu NH2 > PrNH2 > Et2NH. The Bronsted beta coefficient is 0.67 and the Taft's c orrelation coefficient rho (25)* is 4.39 for the primary amines. Two opposi tely charged species seem to be involved in the transition-stale of the sub stitution reactions. A two-step reaction mechanism is consistent with the o bserved results in which the formation of an intermediate is believed to be the rate determining step.