Investigations of Reactions of Selected Azaarenes with Radicals in Water. 2. Chlorine and Bromine Radicals

Abstract

The halogen radicals that react with azaarenes are produced by the photooxidation of halogenide anions with hydroxyl and sulfate radicals and exist as complexes of the radical and the respective halogenide anion in the aqueous phase. The main reaction products of the reactions are identified, and in the case of the bromine radicals, the second order rate constants are determined. Oxidation takes place according to the different redox potentials of the two reactants and is especially observed for chlorine radicals. A typical product spectrum comparable with that in reactions with hydroxyl and sulfate radicals has been found. The formation of some oxidation products in reactions of bromine radicals is in contradistinction to the oxidation potentials of the azaarenes and can be understood only by the reaction of their excited states. The halogenation is the main reaction of the azaarenes. Halogenation products of both, the benzene and the pyridine/diazine rings, have been found. The halogenation of the pyridine/diazine ring again requires the reaction of excited states. The majority of derivatives is halogenated in substitution reactions, but in the reaction of benzo[h]quinoline, addition is also observed. The resonance energy per electron is responsible for the change in the halogenation mechanism from substitution to addition.

Effects of halide ions on photodegradation of sulfonamide antibiotics: Formation of halogenated intermediates

“…Although Br À occurs at a 675-fold lower concentration than Cl À , it is also considered to be an important photoactive constituent in estuarine waters and seawater because of its effects on the photochemical transformation of many pollutants (Beitz et al, 1998). Effects of Br À at estuarine waters concentrations (0.8 mM) on the photodegradation of the SAs were probed.…”

“…To further elucidate the enhancing effects, we compared the values of E T of sulfamethazine with E (Br 2 À /Br À ) ¼ 1.63 V (Beitz et al, 1998). The results show that the value of E T for sulfamethazine is much higher than E (Br 2 $ À /Br À ), indicating that tripletexcited sulfamethazine can oxidize Br À to form Br 2 À .…”

“…Su et al (2016) reported that transformation products containing the isoxazole ring of sulfamethoxazole are photostable and are also resistant to biodegradation. According to the previous studies, halogenated transformation products can possess higher toxicity and stronger persistence than their parent compounds (Beitz et al, 1998;Grebel et al, 2010;Liu et al, 2009;Riu et al, 2011), thus halogenated intermediates of sulfamethazine deserve special attention in the aquatic environment.…”

“…Understanding the halogenation mechanisms of organic pollutants is helpful for the risk assessment of halogenated compounds due to their higher toxicity than parent compounds (Beitz et al, 1998;Grebel et al, 2010;Liu et al, 2009;Riu et al, 2011). Previous studies indicated that halide ions can react with $OH producing halogen radicals, leading to the formation of halogenated products (Grebel et al, 2010;Liu et al, 2009).…”

Measurement of the kinetics of adsorbed cinnoline by square-wave voltammetry

“…Its derivatives have anti-inflammatory and antibiotic activity [15] and are used in synthesis of indoles [16]. Cinnoline is characterized by a stable double bond between nitrogen atoms [17,18,19]; this results in its low reactivity to radicals under environmental conditions [20]. On a mercury electrode in basic electrolytes cinnoline can be reversibly reduced to 1,2-dihydrocinnoline: (2) but in strongly acidic medium the redox reaction is followed by irreversible transformation of the product into 1,4-dihydrocinnoline that cannot be electrooxidized back to cinnoline [21].…”