Kinetics of reaction of 2,4-dinitrophenyl acetate with 3- and 4-substituted Pyridines and 4’-susbstituted 4-styrylpyridines

Abstract

Second order rate constants have been de ermined for the reaction of 2,4-dinitrophenyl acetate with 3- and 4-substituted pyridines and 4'-substituted 4’-styrylpyridines in acetonitrile-water (50%, v/v) mixture at 25°, 30°, 35° and 40°C. Activation parameters have been evaluated. Electron-releasing substituents increase the rate while electron-withdraw in substituents retard it. In both the reaction series linear free energy relationship is found to exist between the logarithms of rate constants and σ constants with ρ = -3.39 ± 0.38 (<em>r</em> <em>= </em>0.989; s = 0.163; n= 12 for 3- and 4-substituted pyridines and ρ = -0.390 ± 0.080 (r = 0.984; s = 0.028; n = 8) for 4'-substituted 4-styrylpyridines at 30°C. The ratio of effectiveness of transmission of substituent effect in styryl system relative to pyridine system in this reaction is 0.115. The Bronsted plot obtained is linear and β_N is found to be 0.692 ± 0.056 (<em>r </em>= 0.990; s= 0.146; n = 16) indicating the extensive bond formation between pyridine and the reaction centre in the transition state.