Ozonation of parabens in aqueous solution: Kinetics and mechanism of degradation

This study investigated the reaction kinetics and degradation mechanism of parabens (methylparaben, ethylparaben, propylparaben and butylparaben) during ozonation. Experiments were performed at pH 2, 6 and 12 to determine the rate constants for the reaction of protonated, undissociated and dissociated paraben with ozone. The rate constants for the reaction of ozone with dissociated parabens (3.3 × 109–4.2 × 109 M−1 s−1) were found to be 104 times higher than the undissociated parabens (2.5 × 105–4.4 × 105 M−1 s−1) and 107 times higher than with the protonated parabens (1.02 × 102–1.38 × 102 M−1 s−1). The second-order rate constants for the reaction between parabens with hydroxyl radicals were found to vary from 6.8 × 109 to 9.2 × 109 M−1 s−1.Characterization of degradation by-products (DBPs) formed during the ozonation of each selected parabens has been carried out using GCMS after silylation. Twenty DBPs formed during ozonation of selected parabens have been identified. Hydroxylation has been found to be the major reaction for the formation of the identified DBPs. Through the hydroxylation reaction, a variety of hydroxylated parabens was formed.