Feed-back action of nitrite in the oxidation of nitrophenols by bicarbonate-activated peroxide system

Abstract

In this study it was found that the nitrite anion greatly increases the oxidation rate o fthe substituted phenols by the bicarbonate-activated peroxide (BAP) system at ambient temperature. This feed-back effect was investigated in the BAP oxidation of 2-amino-4-nitrophenol and 4-nitrophenol, where the kinetic analysis showed that the rate determining step was the elimination of a nitro group as nitrite. Complementary oxidation experiments with 2-aminophenol in BAP system, performed in the presence/absence of sodium nitrite confirmed the catalytic role of this anion. High concentrations of nitrite/BAP prevented formation of polymeric species and favoured the degradation to aliphatic fragments such as 3-oxobutanoic and acetic acid. Indirect evidence suggested in-situ generation of reactive oxygen species (ROS), other than hydroxyl, peroxyl and carbonate radicals, during the nitrite/BAP oxidation. Formation of additional ROS – peroxynitrite and nitrosoperoxycarbonate – may account the synergistic action of nitrite/BAP system. The estimated value of the apparent rate constant of the autocatalytic step for 2-amino-4-nitrophenol (kapp = (4.97 ± 0.19) × 103 M−3 s−1 ) demonstrates that fast degradation of this oxidation-resistant phenolic dye is feasible even in ambient conditions. These findings can be exploited for developing clean, cost-effective methods for the removal of phenolic dyes as alternative to current advanced oxidation processes.