Solvent Effects on the Kinetics of Amide Bond Cleavage in p-Chloro and p-Bromo Oxazolinones in Acetonitrile-Water Mixtures

The kinetics of amide bond cleavage in p-chloro and p-bromo oxazolinone have been studied using triethylamine as a base catalyst under pseudo-first order conditions, in the temperature range (303.15-333.15 K). The reaction rate was measured spectrophotometrically over a range of acetonitrile-water mixed solvent (30-70 %, v/v) compositions. The reaction rate was found to be faster for p-Cl than for p-Br oxazolinone. The thermodynamic parameters of activation were calculated: a dagger G* increased gradually as the mole fraction of the cosolvent increased due to quasi-mirror image compensation of a dagger H* and a dagger S* (entropy-enthalpy compensation). The isokinetic temperature indicates that the reaction is enthalpy controlled. The reactivity was analyzed in the light of various simple and multiple regression equations using the Kamlet-Taft solvatochromic parameters.