Transformation of Acetaminophen by Dichromate Oxidation Produces the Toxicants 1,4-Benzoquinone and Ammonium Ions

Abstract

The reaction of the common pain reliever acetaminophen (paracetamol, 4-acetamidophenol) with dichromate was investigated over time under conditions that simulate wastewater disinfection. The occurrence of the acetaminophen in the water bodies, especially in drinking water resources, has received considerable attentions. In situ chemical oxidation is a promising cost-effective treatment method to remove acetaminophen from water body as it degrades the drug to large extent. Experimental results indicate that the reaction is second order overall and first order with respect to both dichromate and acetaminophen, and has activation energy of 14.1 kJ/mol. The second-order rate constant ranges from 1.56 × 10⁻³ to 13.4 × 10⁻³ min⁻¹ at temperature from 35 to 65°C. The acetaminophen degradation rates can be accelerated through increasing reaction temperature and oxidant concentration. The reaction under acid conditions was slightly faster than under alkaline or neutral conditions. Two of the products were unequivocally identified as the toxic compounds 1,4-benzoquinone and ammonium ions. These results demonstrate that acetaminophen is likely to be transformed significantly into toxic product if dichromate is used as an oxidizing agent during wastewater treatment.

Keywords:

• Acetaminophen
• dichromate
• kinetics
• oxidation

Acknowledgments

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

Notes

^a Error limits are standard deviations.

Activation parameters: E_a = 14.1 kJ mol⁻¹; ΔH^# = 11.5 kJ mol⁻¹; ΔS^# = −242 J K⁻¹ mol⁻¹; ΔG^# = 85.9 kJ mol⁻¹.