Products and Kinetics of the OH-radical-induced Dealkylation of Atrazine

Abstract

Hydroxyl radicals, generated radiolytically in N2O/O2‐saturated solutions, yield in their reaction with atrazine equal amounts of deethylatrazine and acetaldehyde (40% of OH radical yield) and deisopropylatrazine and acetone (16%), respectively. The precursors of deethylatrazine and acetaldehyde is their Schiff base which hydrolyzes slowly (OH–‐catalyzed: k = 5.2 dm3 mol–1 s–1). The hydrolysis of the Schiff base of deisopropylatrazine and acetone is too fast to be detected. In a pulse radiolysis experiment, the intermediate formed upon OH‐radical attack (k = 3·109 dm3 mol–1 s–1) has a strong absorption at 440 nm. It decays in the presence of oxygen (k = 1.3·109 dm3 mol–1 s–1), and upon deprotonation [pKa(peroxyl radicals) ≈ 10.5] the peroxyl radicals thus‐formed eliminate superoxide radicals (k = 2.9·105 s–1). s‐Triazine itself reacts much more slowly with OH radicals (k = 9.7·107 dm3 mol–1 s–1). This can explain, why in the case of atrazine in comparison to other aromatic compounds, e.g. toluene, the addition of the OH radical to the ring (estimated at ca. 40%) is of relatively little importance as compared to an H‐abstraction from (activated) positions of the side groups.

Fenton-enhanced γ-radiolysis of cyanuric acid

“…On the other hand, though very slow, • OH reacts with OOOT as at least 30% OOOT is degraded after about a radiation dose of 8000 Gy. It can be reasonably assumed that • OH undergoes addition reaction with OOOT based on the earlier understanding that • OH reacts with many of the triazine ring by addition [11,15,17].…”

“…The pattern of reaction of • OH with a number of triazine derivatives is reasonably well documented [11,15,16]. • OH undergoes either addition or hydrogen abstraction reaction with atrazine [15,16]. It was also shown that the major end product of oxidation of atrazine by • OH is cyanuric acid (OOOT) [17].…”

“…Under these circumstances, a number of other reasons must be considered. The intermediate radicals from the addition reaction of • OH would lead to both oxidizing and reducing radicals [15]. During Fenton reaction, both Fe(II) and Fe(III) will be present in the reaction mixture (see reaction (3)).…”

“…Similar to other pollutants the conventional methods used for the decontamination of wastewater are not effective in the case of triazines and hence more work is being concentrated for the development of new technologies for their complete degradation. There are several reports on the degradation of triazine derivatives using different AOPs [10][11][12][13][14][15][16]. It is seen in all these reports that only a transformation of the atrazine to a relatively less toxic cyanuric acid can be achieved.…”

Gamma-ray induced degradation of diazinon and atrazine in natural groundwaters

“…On the other hand, the rate constants for solvated electrons (e aq − ) with carbonate, bicarbonate and nitrate ions were determined as 3.5 × 10 5 M −1 s −1 , 1.0 × 10 6 M −1 s −1 and 9.7 × 10 9 M −1 s −1 , respectively [22][23][24], consequently a decrease of solvated electrons was expected. In addition, the rate constant for reaction of OH • with atrazine was determined as 3.0 × 10 9 M −1 s −1 [26], whereas the rate constant for reaction of solvated electrons (e aq − ) with atrazine was determined as 4.8 × 10 9 M −1 s −1 [17]. Moreover the radiolytic behavior of atrazine in water is not totally clear whether it follows oxidation reactions [13] or reduction reactions [17,20] and consequently radiolytic degradation of atrazine decreases with increase of groundwater scavengers concentrations due to competition reactions of atrazine and scavengers for OH • radicals and solvated electrons (e aq − ).…”