Kinetics and mechanism of the nucleophilic ring opening of oxazolinone in mixed aqueous solvents

Abstract

Solvent effect on the kinetics of ring opening of oxazolinone has been investigated in neutral and alkaline medium in dioxan-water mixtures up to 50% v/v in the temperature range of 40-60ºC. The thermodynamic activation parameters have been calculated and discussed in terms of solvation effect. The isokinetic temperature in both media (310, 303 and 298 K for neutral, alkaline hydrolysis by NaOH and Na₂CO₃ respectively) indicates that the reaction is entropy controlled and that solute-solvent interactions play an important role. The correlation of logk₂ against either Grunwald-Wientien Y values or log[H₂O] was found to be linear, while the correlation between logk₂ and the reciprocal of the dielectric constant was non-linear. The estimated value of the slope m in Grunwald relationship gives a value less than unity indicating SAN/SN² mechanism. Mechanism for the oxazolinone ring opening has been proposed.