Optimising Bromination of Phenols: Investigating the Role of pH and Oxidizer in Electrophilic Substitution Reaction

This study investigated the influence of pH and the choice of brominating agent (KBr-chKBrO3 vs NBS-KBr) on the kinetics of Phenol bromination for aromatic substitution by altering pH levels and assessing reaction rates using thin-layer chromatography (TLC). The results revealed that the optimal pH for bromination (pH 3-10) was found to be pH 3 for the KBr system (in acetic acid/water) and pH 4 for NBS. Optimal reactivity was observed in acidic media, specifically pH 3, for the NBS system, and in acetonitrile. The activation energy (Ea) for the bromination increased linearly with pH for both systems, indicating a higher energy barrier for the reaction under less acidic conditions. Detailed mechanisms were proposed, involving the generation of active electrophiles via pH-dependent equilibria, followed by rate-determining electrophilic attack on the phenol ring.