New coumarin-based disperse disazo dyes: Synthesis, spectroscopic properties and theoretical calculations

Nontargeted Analysis of Coumarins in Source Water and Their Formation of Chlorinated Coumarins as DBPs in Drinking Water

Coumarin was detected as one of the most abundant compounds by nontargeted analysis of natural product components in actual water samples prior to disinfection. More importantly, prechlorination of humic acid generated 3-hydroxycoumarin and monohydroxy-monomethyl-substituted coumarin with a total yield of ≤10.1%, which suggested the humic substance in raw water is an important source of coumarins. 7-Hydroxycoumarin, 6-hydroxy-4-methylcoumarin, 6,7-dihydroxycoumarin, and 7-methoxy-4-methylcoumarin were identified in raw water by high-performance liquid chromatography-tandem high-resolution mass spectrometry because only some coumarin standards were commercially available. Their chlorination generated monochlorinated and polychlorinated coumarins, and their structures were confirmed by the synthesized standards. These products could form at various dosages of chlorine and pH levels, and some with a concentration of 600 ng/L can be stable in tap water for days. 3,6,8-Trichloro-7-hydroxycoumarin, 3-chloro-7-methoxy-4-methylcoumarin, and 3,6-dichloro-7-methoxy-4-methylcoumarin were first identified in finished water with concentrations of 0.0670, 78.1, and 14.7 ng/L, respectively, but not in source water, suggesting that they are new DBPs formed during disinfection. The cytotoxicity of 3-chloro-7-methoxy-4-methylcoumarin in CHO-K1 cells was comparable to those of 2,6-dibromo-1,4-benzoquinone and 2,6-dichloro-1,4-benzoquinone in TIC-Tox analyses, suggesting that further investigation of their occurrence and control in drinking water systems is warranted.

Overview on developed synthesis procedures of coumarin heterocycles

Considering highly valuable biological and pharmaceutical properties of coumarins, the synthesis of these heterocycles has been considered for many organic and pharmaceutical chemists. This review includes the recent research in synthesis methods of coumarin systems, investigating their biological properties and describing the literature reports for the period of 2016 to the middle of 2020. In this review, we have classified the contents based on co-groups of coumarin ring. These reported methods are carried out in the classical and non-classical conditions particularly under green condition such as using green solvent, catalyst and other procedures.

Chlorine incorporation into dye degradation by-product (coumarin) in UV/peroxymonosulfate process: A negative case of end-of-pipe treatment

Recently, UV/peroxymonosulfate (PMS) seems as a panacea for the treatment of recalcitrant organic pollutants; however, the presence of high concentration of chloride in saline wastewater indeed complicates this end-of-pipe technology. Here a negative case of UV/PMS for the treatment of one of secondary degradation byproducts of dyes (coumarin, COU) is demonstrated. The removal rate of COU is reduced by addition of Cl^- (0-10 mM). Further increase in Cl^- content favors a rapid COU degradation, whereas Cl^- involvement seems to open a "Pandora's box": 1) a variety of chlorinated organic intermediates such as 4-chloroisocoumarin and 5-chloro-2-hydroxy-benzaldehyde are identified; 2) Accumulation and relative increase of absorbable organic halogen (AOX) with reaction time in the presence of high levels of chloride are observed; 3) the acute toxicity of the treated COU solution increases; 4) mineralization rate of COU decreases with the increasing [Cl^-]. The fluorescence intensity in the UV/PMS/COU system declines with the addition of Cl^-, implying the scavenging effects of chloride on hydroxyl radicals. The possible reaction pathways of COU are discussed. These findings highlight the imperativeness of minimizing auxiliary salt dosages in dyeing processes (i.e., source reduction) and developing new end-of-pipe technologies that can work in a saline environment.