Radiolytic oxidation and degradation of 2,4-dichlorophenol in aqueous solutions

Radiolytic oxidation of 2,4-dichlorophenol (2,4-DClP) in aqueous solutions demonstrated that ·OH predominantly adds to the unsubstituted positions of the aromatic ring and that elimination of chloride at the 4 position is important because the –OH group enhances the electron density at this position, which is favorable for the electrophilic reactions. The total yield obtained was 0.540 μmol/J. Radiation-induced degradation of 2,4-DClP was conducted in oxygen-free aqueous solutions (0.1, 0.25, 0.50, and 0.7 mmol/dm3), saturated with N2O, and aerated and under irradiation at low and high doses. The results demonstrate that the largest degradation occurred in oxygen-free solutions due to oxidation (·OH) and reduction reactions (H· and $$ {\mathrm{e}}_{\mathrm{aq}}^{-} $$ ) and attack of the $$ {\mathrm{e}}_{\mathrm{aq}}^{-} $$ at the ipso position of –Cl, producing HCl. The degradation was affected to a large extent by the concentration and to a lesser extent by the presence or absence of oxygen in which the 2,4-DClP solution was irradiated. At concentrations less than 1 mmol/dm3, 2,4-DClP was degraded in the solution at an absorbed dose level of 1 kGy. At higher doses, the product concentrations increased to up to 30% of the dose required for the total degradation of 2,4-DClP; then, they decreased. A graph plotting the logarithm of the relative concentration as a function of the dose shows a linear correlation, which indicates that the radiolytic degradation followed pseudo-first-order reaction kinetics. The oxidation was followed by the chemical oxygen demand (COD). COD decreases when the solute concentration increases. This fact has a dependence on the presence or absence of oxygen too.