Stepwise Mechanisms of the Aminolyses of 4-Nitrophenyl and 2,4-Dinitrophenyl O-Ethyl Dithiocarbonates in Aqueous Ethanol

Article abstract of DOI:10.1002/kin.550271004

The reactions of the title substrates with a series of secondary alicyclic amines are subjected to a kinetic study in 44 wtpercent aqueous ethanol, at 25.0 deg C, ionic strength 0.2 M (maintained with KCl).Pseudo-first-order kinetics are found under amine excess.The order in amine obtained is one in the reactions of all amines.The Broensted-type plots for the overall second-order rate coefficients are biphasic with slopes β₁ = 0.3 (high pK_a), β₂ = 0.95 (low pK_a) for the aminolysis of the 4-nitro derivative, and β₁ = 0.3 and β₂ = 0.80 for the aminolysis of the dinitro compound; the pK_a values at the curvature center are pK⁰_a 9.8 and 9.5, respectively.From a comparison of these pK⁰_a values with those found in the same reactions in water and the shapes of the Broensted-type plots, it is concluded that these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate in the reaction pathway.