Visible‐Light‐Sensitized Dechlorination of Perchloroethylene

Abstract

An aqueous reaction mixture containing perchloroethylene (PCE), a photosensitizer, and an electron donor was irradiated by visible lamps to facilitate a sunlight-sensitized dechlorination reaction. Various types of lamps, electron donors, and photosensitizers were examined, to compare the rates of dechlorination. Of the six photosensitizers evaluated, methylene blue was the most effective. Electron donors varied in effectiveness, as follows: trimethylamine . triethylamine . tributylamine. The intermediates and reaction products were identified by a purge-and-trap gas chromatography mass spectrometer system. The photosensitized dechlorination method degraded PCE via an electron-transfer-relay mechanism. Degradation products identified were trichloroethylene, dichloroethylenes, and chloroethylene. It seems a sequential dechlorination pathway was followed. The PCE dechlorination in a natural sunlight irradiation test was shown to be more effective than any of the simulated visible light sources. The result supports the feasibility of future development of solarpowered dechlorination remediation systems with the use of sunlight, nontoxic dyes, and electron donors. Water Environ. Res., 81, 76 (2009).

Method validation and characterization of stress degradation products of azelastine hydrochloride using LC‐UV/PDA and LC‐Q/TOF‐MS studies

“…Product III could be generated by photocatalyzed Ndemethylation (similar to products I and II) followed by photocatalyzed dechlorination to its corresponding hydroxyl derivative. 40 A similar dehalogenation of lomefloxacin over the entire pH range (pH 1-10) to its hydroxyl derivative has been previously documented. 41 Photolytic dehalogenation was followed by a two-step N-dealkylation of azepine ring, which resulted in the formation of Product III by removal of ammonia molecule.…”

“…Product III , characterized as 2‐(1,6‐dihydroxyhexan‐3‐yl)‐4‐(4‐hydroxybenzyl)phthalazin‐1( 2H )‐one, was generated under acid photolytic, base photolytic, and neutral photolytic conditions (Figure 7). Product III could be generated by photocatalyzed N ‐demethylation (similar to products I and II ) followed by photocatalyzed dechlorination to its corresponding hydroxyl derivative 40 . A similar dehalogenation of lomefloxacin over the entire pH range (pH 1–10) to its hydroxyl derivative has been previously documented 41 .…”

“…Product IV , proposed as 3‐(6‐hydroxy‐4‐(4‐hydroxybenzyl)‐1‐oxophthalazin‐2(1H)‐yl)hexanedioic acid, was generated in alkaline photolytic conditions (Figure 7). Azelastine could undergo alkaline photolytic N ‐demethylation (similar to Product II ), followed by photocatalyzed dechlorination to the corresponding hydroxyl derivative as in the case of Product III 40 . Alkaline photolytic dehalogenation was followed by the epoxidation of benzene ring and subsequent ring opening) 43 and two steps of ring N ‐dealkylation (in the azepine ring), which led to the removal of an ammonia molecule, resulting in the formation of a diol system 39,42,44 .…”

“…Azelastine could undergo alkaline photolytic N-demethylation (similar to Product II), followed by photocatalyzed dechlorination to the corresponding hydroxyl derivative as in the case of Product III. 40 Alkaline photolytic dehalogenation was followed by the epoxidation of benzene ring and subsequent ring opening) 43 and two steps of ring N-dealkylation (in the azepine ring), which led to the removal of an ammonia molecule, resulting in the formation of a diol system. 39,42,44 This diol system was photo-oxidized further to form the dicarboxylic acid (Product IV).…”