Exploring the oxidation chemistry of hydroxy naphthoic acid: An experimental and theoretical study

Abstract

AbstractElimination of polycyclic aromatic hydrocarbons (PAHs) from aquatic environment is extremely important, as they are identified pollutants. The oxidative degradation of two model PAHs, namely 3‐hydroxy‐2‐naphthoic acid (3HNA) and 6‐hydroxy‐2‐naphthoic acid (6HNA), collectively represented as HNAs in this report, were investigated by utilizing a combined approach of pulse radiolysis, theoretical studies and high‐resolution mass spectrometry (HRMS). Hydroxylated adduct radicals of HNAs (3HNA–λmax; 340 nm; k2 = [1.09 ± 0.07] × 1010 dm3 mol−1 s−1, 6HNA–λmax; 350 nm; k2 = [9.43 ± 0.05] × 109 dm3 mol−1 s−1) were recognized as the immediate intermediates upon their reaction with hydroxyl radical (•OH). While theoretical calculations revealed the contributions from C1 and C4 adducts into the experimentally observed spectrum of 3HNA, the C5 adduct accounted as the major contributor for 6HNA. Investigations using specific oxidants, such as sulfate (SO4•−) and oxide (O•−) radicals, helped to exclude the contributions from other minor pathways (e.g., one‐electron oxidation and hydrogen abstraction). Further, HRMS studies revealed the existence of mono‐ and multi‐hydroxylated derivatives of HNAs as well as many other oxidation products including quinone‐like and ring‐opened structures. The in‐depth mechanistic aspects, including the kinetic and product profile, furnished in this report provide detailed insights in to the oxidation chemistry of highly toxic PAHs, such as the HNAs, in the aquatic environment.