Revisiting the Role of Tertiary Amines in Enhancing Aqueous Chlorination of Phenolic Compounds: Kinetic Modeling and Reaction Mechanisms

Tertiary amines in dissolved organic nitrogen have been implicated for decades in mediating organic chlorination through the formation of reactive quaternary ammonium intermediates (R₃N⁺-Cl), yet the mechanistic underpinnings of this process remain poorly understood. This study presents the first systematic investigation of structure-activity relationships (SARs) governing tertiary amine-enhanced chlorination using phenolic compounds as representative substrates. Through advanced kinetic analyses, we demonstrate that catalytic chlorination efficiency correlates directly with the Brønsted-Lowry basicity of tertiary amines, mechanistically linked to the stabilization of R₃N⁺-Cl species. A MATLAB-based approach coupled with Kintecus modeling was used to quantify the R₃N⁺-Cl reactivity with phenolics (2.86 × 10⁴-2.29 × 10⁵ M^-1 s^-1), previously uncharted kinetic parameters critical for predictive water treatment modeling. Environmental relevance was indicated through matrix interference studies, showing ∼10% reduction in phenol removal efficiency by Fe³⁺ or humic acid in the chlorine/trimethylamine system. Product analysis revealed conserved chlorination pathways without new byproduct formation, while the chlorinated bisphenol derivatives exhibited moderate-to-high endocrine-disrupting activity. This work fundamentally advances our understanding of amine-mediated chlorination mechanisms by revealing critical water quality implications through combined kinetic and toxicological assessments. The findings provide essential mechanistic insights for optimizing chlorination processes in tertiary amine-containing waters while highlighting previously underestimated risks from accelerated formation of bioactive chlorinated compounds.