# Experimental and Theoretical Studies on Reaction Kinetics, Mechanism, and Degradation of Quinoline‐Based Herbicide with Hydroxyl Radical, Sulphate Radical Anion, and Hydrated Electron

## TL;DR

This study explores how a quinoline-based herbicide reacts with reactive radicals under different pH conditions, combining experiments and theory to understand degradation mechanisms.

## Contribution

The paper provides a combined experimental and theoretical analysis of 8QCA degradation pathways by hydroxyl and sulfate radicals under varying pH conditions.

## Key findings

- At pH 1, protonated 8QCA reacts with •OH to form transient products with absorption maxima at 340 and 420 nm.
- At pH 9, deprotonated 8QCA shows transient absorption at 320 nm when reacting with •OH.
- Theoretical calculations confirm C5 carbon as the most reactive site for •OH radical addition.

## Abstract

The kinetic and mechanistic studies for the reaction of hydroxyl radical (•OH), sulfate radical anion (SO4•−), and hydrated electron (eaq−) with quinoline‐based herbicide, namely, 8–quinoline carboxylic acid (8QCA), have been performed using experimental and computational methods. Experimental studies are performed using pulse radiolysis technique at different pHs and corroborated with theoretical studies using ab initio molecular orbital calculations. At lower pH of 1, the 8QCA is protonated and reacts with •OH radical to generate transient spectrum with maxima at 340 and 420 nm. Similarly at higher pH of 9, the 8QCA is deprotonated and shows transient absorption maxima at 320 nm. At neutral pH, it exists as neutral species and reacts with •OH radical differently. Theoretically, individual rate coefficients for •OH radical addition reaction with each carbon atoms are evaluated including solvent effect and tunneling correction. Fukui index and individual rate constant determination confirm that C5 carbon atom is the most reactive site for the •OH radical addition reaction. The total rate constant evaluated theoretically and experimentally for the •OH radical reaction is equal to its diffusion‐limit value. The ability of •OH radical to degrade 8QCA is found to be higher as compared to eaq−.

Advanced oxidative process is commonly used for the degradation/removal of herbicides from soil/water bodies. It mostly involves oxidizing •OH and SO4•− species. The present study involves an experimental and theoretical approach to explore kinetics, mechanism, and degradation pathways for 8–quinoline carboxylic acid (8QCA), which has basic structure for two herbicides, namely, quinclorac and quinmerac. © 2025 WILEY‐VCH GmbH