Kinetics and mechanism of the pyridinolysis of 2,4-dinitrophenyl p-nitrobenzoate

Abstract

The nucleophilic reactions of a series of 3- and 4-monosubstituted pyridines with 2,4-dinitrophenyl p-nitrobenzoate are studied in 44 wt% aqueous ethanol at 25 °C, and ionic strength 0.2 mol dm^–3(sodium perchlorate). The Brönsted-type plot obtained (log second-order rate constant against basicity of the pyridine) is straight, in contrast to the ones found in the pyridinolyses of 2,4-dinitrophenyl acetate and 2,4-dinitrophenyl methyl carbonate, and in the reactions of substituted quinuclidines with 2,4-dinitrophenyl phenyl carbonate, which all exhibit curved Brönsted plots centred at pK_a°7.3–7.8. The higher pK_a° value obtained in the title reactions (>8.9) is explained mainly by the large influence of the electron withdrawing power of the non-leaving group of the substrate.