The bromination kinetics of phenolic compounds in aqueous solution

The purpose of this study was to investigate the bromination kinetics of selected phenolic compounds in aqueous solutions over the pH range of 5-11. The experiment results indicated that the reaction of hypobromous acid with the phenoxide ions controlled the overall reaction rate, whereas the reaction between hypobromite ion and the phenoxide ions and the reaction between hypobromous acid and the undissociated phenolic species were considered to be negligible respectively in the pH range of 7-9. The apparent second-order rate constants of the reaction of hypobromous acid with the phenoxide ions ranged from 7.9 × 106 M−1 s−1 for 3-chlorophenol to 6.5 × 108 M−1 s−1 for 3-methoxyphenol, respectively. The Hammett correlation could be successfully used to estimate the reactivity of bromine with substituted phenols and the linear regression was log(k2) = −2.85б + 8.00. The rate constants of the reaction of bromine with phenol-like organic compounds were about three orders of magnitude higher than with chlorine and two to three orders of magnitude lower than with ozone.