Kinetic, Mechanistic, and Quantum Chemical Study of Osmium(VIII)-Catalyzed Bromination of Paracetamol by Acidic N-Bromosuccinimide (Iodometric Titration).

The kinetics and mechanism of osmium(VIII)-catalyzed oxidation of paracetamol (PAM) with N-bromosuccinimide (NBS) in acidic medium have been studied at a constant ionic strength of 0.50 M. The reaction is characterized by 1:1 stoichiometry. The main products were identified by spot test and IR and UV-visible spectroscopy. The activation parameters of the rate-determining step were computed and discussed, and the thermodynamic parameters were also calculated. First-order kinetics with respect to Os(VIII) was observed for the oxidation of paracetamol. The reaction rate decreased with increase in the acidity and NBS concentration. Variation of the ionic strength had no significant effect on the reaction rate. A plausible mechanism has been proposed on the basis of the kinetic studies, reaction stoichiometry, and product analysis. Quantum chemical study of the oxidation of paracetamol with NBS was performed in the framework of the density functional theory (DFT) using B3LYP/6-31G(d,p) basis set. The DFT studies included computation of various structural parameters, viz. electrostatic potential, electrophilicity, chemical potential, chemical hardness, thermodynamic properties at various temperatures, nonlinear optical (NLO) properties, Mulliken charges, electric dipole moments, polarizability, and first static hyperpolarizability, as well as natural bond orbital (NBO) and atom in molecule (AIM) analysis. [ABSTRACT FROM AUTHOR]