Kinetics of proton and deuteron transfer from α,4-dinitrotoluene to 1,8-bis(dimethylamino)naphthalene in alcoholic solvents

Abstract

Evidence is presented to show that the reaction between α,4-dinitrotoluene and 1,8-bis(dimethylamino)naphthalene, in either propan-2-ol or t-butyl alcohol as solvent, is a proton transfer from the carbon acid to the nitrogen base to give an ion pair. The second-order rate constants for the proton and deuteron transfer reactions have been determined over the temperature range 10–45 °C in the two solvents. The reactions are relatively slow and are characterized by enthalpies of activation of 10–14 kcal mol^–1(42–58 kJ mol^–1) and entropies of activation of –17 to –31 cal mol^–1 K^–1(–71 to –130 J mol^–1 K^–1). The isotopic rate ratios are small (k_H/k_D < 3), although ΔH_D^‡–ΔH_H^‡ is normal (ca. 1 kcal mol^–1), with compensation by positive values for ΔS_D^‡–ΔS_H^‡.