Acetaminophen is widely used to treat mild to moderate
pain and
to reduce fever. Under the worldwide COVID-19 pandemic, this over-the-counter
pain reliever and fever reducer has been drastically consumed, which
makes it even more abundant than ever in municipal wastewater and
drinking water sources. Chlorine is the most widely used oxidant in
drinking water disinfection, and chlorination generally causes the
degradation of organic compounds, including acetaminophen. In this
study, a new reaction pathway in the chlorination of acetaminophen,
i.e., oxidative coupling reactions via acetaminophen radicals, was
investigated both experimentally and computationally. Using an ultraperformance
liquid chromatograph coupled to an electrospray ionization-triple
quadrupole mass spectrometer, we detected over 20 polymeric products
in chlorinated acetaminophen samples, some of which have structures
similar to the legacy pollutants “polychlorinated biphenyls”.
Both C–C and C–O bonding products were found, and the
corresponding bonding processes and kinetics were revealed by quantum
chemical calculations. Based on the product confirmation and intrinsic
reaction coordinate computations, a pathway for the formation of the
polymeric products in the chlorination of acetaminophen was proposed.
This study suggests that chlorination may cause not only degradation
but also upgradation of a phenolic compound or contaminant.