Solvent parameters effects on the second-order rate constants of the reaction of 2-chloro-3,5-dinitropyridine with aniline in aqueous solutions of alcohols

Aromatic nucleophilic substitution reaction kinetics of 2-chloro-3,5-dinitropyridine with aniline was studied in aqueous solutions of methanol, ethanol, and 2-propanol at room temperature. The obtained results for aqueous solutions indicate that the second-order rate constants are in order of 2-propanol > ethanol > methanol with a maximum at water mole fraction of 0.9. The influence of solvent parameters including normalized polarity (E-T(N)), dipolarity/polarisability (pi*), and hydrogen bond donor acidity (alpha) on the second-order rate constants were investigated and multiple regressions gave much better results with regard to single parameter regressions. Dipolarity/polarisability and hydrogen bond donor acidity of media demonstrate opposite effects on the reaction rate. The dipolarity/polarisability of media has a positive effect regarding to zwitterionic character of the reaction intermediate and the hydrogen bond donor acidity shows a negative effect because of hydrogen-bonding interactions between aniline and solvent molecules.