Oxidative Degradation of Acetaminophen by Permanganate in Neutral Medium-A Kinetic and Mechanistic Pathway

Abstract

The occurrence of pharmaceuticals in the environment is an emerging issue. Several studies observed that the nonsteroidal antiinflammatory drug acetaminophen is ubiquitously present in most of the surveyed surface waters, worldwide. This spectroscopic study presents the kinetics and degradation pathways of oxidation of acetaminophen by permanganate in neutral medium. The variables affecting the reactions were carefully investigated and the conditions were optimized. The higher degradation rate was observed with increase in acetaminophen concentration in the range of 0.4 × 10⁻³ to 9.7 × 10⁻³ min⁻¹. The retention time and UV-visible absorption spectrum of the product were found to be identical to those of p-benzoquinone. The spectral change in the course of reaction was observed in the region 400 nm to 700 nm and there was a gradual decrease in absorption intensity at its λ_max. Kinetic analysis of these results only gave good linear plots, with regression coefficients >0.996, when they were fitted to a pseudo-first-order reaction. The slope of log k versus 1/T also confirms the first-order dependence on the reactant. Investigations of the reaction at different temperatures allowed the determination of the activation parameters with respect to the slow step of proposed mechanism.

Keywords:

• Acetaminophen
• kinetic
• oxidation
• permanganate

Acknowledgements

The authors express their gratitude to the Chairman, Department of Chemistry, Aligarh Muslim University, Aligarh, and Universiti Sains Malaysia, Malaysia, for postdoctoral grant support and providing the research facilities.

Notes

^aError limits are standard deviations.

Activation parameters: E_a = 23.9 kJmol⁻¹.

ΔH^# = 21.4 kJmol⁻¹; ΔS^# = −225 JK⁻¹mol⁻¹; ΔG^# = 88.4 kJmol⁻¹.