3018-12-0Relevant articles and documents
Ciprofloxacin degradation in UV/chlorine advanced oxidation process: Influencing factors, mechanisms and degradation pathways
Deng, Jia,Wu, Guangxue,Yuan, Shoujun,Zhan, Xinmin,Wang, Wei,Hu, Zhen-Hu
, p. 151 - 158 (2018/11/24)
Ciprofloxacin (CIP) is a widely used third generation fluoroquinolone antibiotics, and has been often detected in wastewater treatment plants. Finding an effective way to remove them from wastewater is of great concern. Ultraviolet (UV)/chlorine advanced oxidation process (AOP) has many advantages in micropollutant removal. In this study, CIP degradation in UV/chlorine process was investigated. Only 41.2% of CIP was degraded by UV photolysis and 30.5% by dark chlorination in 30 min, while 98.5% of CIP was degraded by UV/chlorine process in 9 min. HCO3 ? had markedly inhibition, NO3 ? and SO4 2- had slight inhibition, and Cl? had a marginal inhibition on CIP degradation in UV/chlorine system. The degradation of CIP in UV/chlorine process was mainly attributed to the attack of reactive species. The relative contributions of hydrated electrons (eaq [rad]), hydroxyl radicals (HO[rad]), chlorine atoms (Cl[rad]), and UV photolysis were investigated. Under neutral condition in aqueous solution, CIP degradation had highest pseudo first-order reaction rate constant, in which eaq [rad] had the highest contribution, followed by Cl[rad], HO[rad], and UV photolysis. The intermediates and byproducts were identified and the degradation pathway was proposed. The total organic chlorine (TOCl) and biotoxicity were further assessed. CIP and natural organic matters (NOMs) were removed efficiently in real water. UV/chlorine showed the potential for the wastewater treatment containing CIP.
Transformation of chlorinated aliphatic compounds by ferruginous smectite
Cervini-Silva,Larson,Wu,Stucki
, p. 805 - 809 (2007/10/03)
A series of chlorinated aliphatic compounds (RCI, including carbon tetrachloride (PCM), 1,1,1-trichloroethane (TCA), 1,1,2,2-tetrachloroethane (TeCA), pentachloroethane (PCA), hexachloroethane (HCA), trichloroethene (TCE), tetrachloroethene (PCE), trichloronitromethane (chloropicrin, CP), and trichloroacetonitrile (TCAN)) was reacted with ferruginuous smectite (sample SWa-1 from The Source Clays Repository), SWa, in aqueous suspension under anoxic conditions. Compounds highly polarizable or sharing substituents that facilitate charge delocalization adsorbed faster by reduced (SWa-R) than by unaltered (SWa-U) clay, indicating stronger dipole-dipole interactions between the substituents and the clay surface and/or hydrating water molecules. The reduction of the clay accelerated RCI adsorption up to 100-fold. Incubations with SWa-R promoted RCI reduction (CP, TCAN) or dehydrochlorination (TeCA and PCA). The reduction of structural Fe catalyzes the transformation of RCI via Bronsted and Lewis-basic promoted pathways. This study indicates that oxidation state of the structural Fe in SWa greatly alters surface chemistry and has a large impact on clay-organic interactions.
Breakpoint chemistry and volatile byproduct formation resulting from chlorination of model organic-N compounds
Shang, Chii,Gong, Woei-Long,Blatchley III, Ernest R.
, p. 1721 - 1728 (2007/10/03)
Aqueous solutions containing six model organic-N compounds (glycine, cysteine, asparagine, uracil, cytosine, and guanine) were subjected to chlorination at various chlorine (CI) to precursor (P) molar ratios for 30 min. Chlorine residuals were determined by both DPD/FAS titration and the MIMS (Membrane Introduction Mass Spectrometry) method to evaluate breakpoint chlorination behavior, residual chlorine distributions, and byproducts. DPD/FAS titration was found to yield false-positive measurements of inorganic combined chlorine residuals in all cases. The breakpoint chlorination curve shape was strongly influenced by the structure of the model compound. Cyanogen chloride was found to be present as a byproduct in all cases, and the yield was strongly dependent on the CI:P molar ratio and the structure of the compounds, with glycine being the most efficient CNCI precursor. Six byproducts other than cyanogen chloride were also identified. Free chlorine measurements by DPD/FAS titration and MIMS were in good agreement. This finding, together with the results of previously conducted research, suggests that both methods are capable of yielding accurate measurements of free chlorine concentration, even in solutions that contain complex mixtures of +1-valent chlorine compounds. Aqueous solutions containing six model organic-N compounds (glycine, cysteine, asparagine, uracil, cytosine, and guanine) were subjected to chlorination at various chlorine (Cl) to precursor (P) molar ratios for 30 min. Chlorine residuals were determined by both DPD/FAS titration and the MIMS (Membrane Introduction Mass Spectrometry) method to evaluate breakpoint chlorination behavior, residual chlorine distributions, and byproducts. DPD/FAS titration was found to yield false-positive measurements of inorganic combined chlorine residuals in all cases. The breakpoint chlorination curve shape was strongly influenced by the structure of the model compound. Cyanogen chloride was found to be present as a byproduct in all cases, and the yield was strongly dependent on the Cl:P molar ratio and the structure of the compounds, with glycine being the most efficient CNCl precursor. Six byproducts other than cyanogen chloride were also identified. Free chlorine measurements by DPD/FAS titration and MIMS were in good agreement. This finding, together with the results of previously conducted research, suggests that both methods are capable of yielding accurate measurements of free chlorine concentration, even in solutions that contain complex mixtures of +1-valent chlorine compounds.
Chemistry of the biosynthesis of halogenated methanes: C1-organohalogens as pre-industrial chemical stressors in the environment?
Urhahn, Thorsten,Ballschmiter, Karlheinz
, p. 1017 - 1032 (2007/10/03)
We have chemical evidence that in the biosynthesis of the halomethanes C1H(4-n),X(n) (n = 1-4) three different pathways of biogenic formation have to be distinguished. The formation of methyl chloride, methyl bromide, and methyl iodide, respectively, has to be considered as a methylation of the respective halide ions. The dihalo- and trihalomethanes are formed via the haloform and/or via the sulfo-haloform reaction. The possible formation of tetrahalomethanes may involve a radical mechanism. Methionine methyl sulfonium chloride used as substrate in the incubation together with chloroperoxidase (CPO) and H2O2 gave high yields of monohalomethanes only. We were able to show that next to the CPO/H2O2 driven haloform reaction of carbonyl activated methyl groups also methyl-sulphur compounds - e.g. dimethylsulfoxide, dimethylsulfone, and the sulphur amino acid methionine - can act as precursors for the biosynthesis of di- and trihalogenated methanes. Moreover, there is some but not yet very conclusive evidence for an enzymatic production of tetrahalogenated methanes. In our experiments with chloroperoxidase involving amino acids and complex natural peptide based substrates, dihalogenated acetonitriles and several other volatile halogenated but yet unidentified compounds were formed. On the basis of these experiments we like to suggest that biosynthesis of halogenated nitriles occurs in general and therefore a natural atmospheric background should exist for halogenated acetonitriles and halogenated acetaldehydes, respectively.
Kinetics of the reactions of acetonitrile with chlorine and fluorine atoms
Tyndall, Geoffrey S.,Orlando, John J.,Wallington, Timothy J.,Sehested, Jens,Nielsen, Ole J.
, p. 660 - 668 (2007/10/03)
The rate coefficients for the reactions of chlorine and fluorine atoms with acetonitrile have been measured using relative and direct methods. In the case of chlorine atoms the rate coefficient k1 was measured between 274 and 345 K using competitive chlorination and at 296 K using laser flash photolysis with atomic resonance fluorescence. The rate coefficient measured at ambient temperature (296 ± 2 K) is (1.15 ± 0.20) × 10-14 cm3 molecule-1 s-1, independent of pressure between 5 and 700 Torr (uncertainties are 2 standard deviations throughout). This result is a factor of 6 higher than the currently accepted value. The results from the three independent determinations reported here yield the Arrhenius expression k1 = (1.6 ± 0.2) × 10-11 exp[-(2140 ± 200)/T] cm3 molecule-1 s-1. Product studies show that the reaction of Cl atoms with CH3CN proceeds predominantly, if not exclusively, by hydrogen abstraction at 296 K. The rate coefficient for the reaction of fluorine atoms with acetonitrile was measured using both the relative rate technique and pulse radiolysis with time-resolved ultraviolet absorption spectroscopy. The rate coefficient for the reaction of F atoms with CH3-CN was found to be dependent on total pressure. The observed rate data could be fitted using the Troe expression with Fc = 0.6, k0 = (2.9 ± 2.1) × 10-28 cm6 molecule-2 s-1, and k∞ = (5.8 ± 0.8) × 10-11 cm3 molecule-1 s-1, with a zero pressure intercept of (0.9 ± 0.4) × 10-11 cm3 molecule-1 s-1. The kinetic data suggest that the reaction of F atoms with CH3CN proceeds via two channels: a pressure-independent H atom abstraction mechanism and a pressure-dependent addition mechanism. Consistent with this hypothesis, two products were observed using pulsed radiolysis with detection by UV absorption spectroscopy. As part of the product studies, relative rate techniques were used to measure k(Cl+CH2ClCN) = (2.8 ± 0.4) × 10-14 and k(F+CH2FCN) = (3.6 ± 0.2) × 10-11 cm3 molecule-1 s-1.
REACTION OF N-BENZYLIDENEPERCHLOROVINYLAMINE WITH PRIMARY AND SECONDARY AMINES
Drach, B. S.,Popovich, T. P.,Kisilenko, A. A.,Kalinin, V. N.,Soifer, G. B.,Gordeev, A. D.
, p. 1093 - 1099 (2007/10/02)
When N-benzylideneperchlorovinylamine (C6H5CH=NCCl=CCl2) is reacted with highly basic secondary amines, a rearrangement occurs already under mild conditions, and substituted amino nitriles with the general formula C6H5CH(NR2)CCl2CN, whose structure was rigorously proved by chemical and spectral methods, form unexpectedly.Primary amines react differently with N-benzylideneperchlorovinylamine, and the main reaction products are N-benzylidenealkylamines and dichloroacetonitrile.
