Reaction Of Chloramine Research Articles

Unconventional Pathways in Nitrogen-Centered SN2 Reactions: From Roundabout to Hydride Transfer.

The mechanisms and dynamics of bimolecular nucleophilic substitution (SN2) reactions are complex and influenced by the nature of the central atom. In this study, we explore SN2 at a nitrogen center (SN2@N) by investigating the reaction of chloramine (NH2Cl) with methoxide ion (CH3O-) using ab initio classical trajectory simulations at the MP2(fc)/aug-cc-pVDZ level of theory. We observe that, in addition to the expected SN2 product formation (CH3ONH2 + Cl-), a high-energy proton-transfer pathway leading to CH3OH and NHCl- dominates, with near-quantitative agreement between simulations and experimental data. Notably, we identify a novel hydride-transfer pathway yielding NH3, H2CO, and Cl-, revealing alternative reactivity channels previously uncharacterized in nitrogen-centered SN2 reactions. Mechanistic analysis uncovers unconventional roaming-mediated and roundabout pathways alongside the traditional direct rebound and indirect mechanisms. Additionally, an umbrella inversion of the NH2 group resulting in retention of configuration in the CH3ONH2 product was observed in a fraction of trajectories.

Computational Studies of Nucleophilic Substitution at Nitrogen Center: Reactions of NH2Cl with HO-, CH3O- and C2H5O.

The atomic-level mechanisms of the nucleophilic substitution reactions at the nitrogen center (SN2@N) were investigated for the reactions of chloramine (NH2Cl) with the alkoxide ions (RO-, where R=H, CH3, and C2H5) using DFT and MP2 methods. The computed potential energy profiles for the SN2@N pathways involving the back-side attack of the nucleophiles show the typical double-well potential with submerged barriers similar to the SN2 reactions at the carbon center (SN2@C). However, the pre-reaction and post-reaction complexes are, respectively, the N-H⋅⋅⋅O and N-H⋅⋅⋅Cl hydrogen-bonded intermediates, which are different from those generally seen in SN2@C reactions. The SN2@N pathways involving front-side attack of the nucleophiles have high-energy barriers. The potential energy surfaces (PESs) along the proton-transfer pathways were flat. In addition to the proton-transfer and SN2 pathways, we also observed a new path for the methoxide and ethoxide nucleophiles where a hydride-transfer from the nucleophile to chloramine resulted in the products Cl-+R'CHO+NH3, (R'=H, CH3), and was the most exoergic. A comparison of the energetics obtained used different DFT and MP2 methods with that of the benchmark coupled-cluster methods reveals that CAM-B3LYP best describes the PESs.

Kinetics of chlorine and chloramine reactions in reverse osmosis permeate and their impact on radical formation during UV/chlorine advanced oxidation for potable reuse

Knowledge of the speciation of chlorine and chloramines in reverse osmosis (RO) permeate is needed to estimate the performance (i.e., pollutant log reduction) of subsequent UV/chlorine advanced oxidation processes (AOPs). To accurately predict the speciation, a previously reported breakpoint chlorination kinetic model was experimentally validated for pH 5.5 and reaction times < 3 min and used to predict the kinetics of breakpoint chlorination in RO permeate. The predictions showed that eliminating chloramines by adding chlorine at a dose beyond the chlorine-to-nitrogen (Cl/N) breakpoint ratio is not practical due to the high breakpoint Cl/N ratio for RO permeate (∼3.0 molar ratio) and an estimated > 40 min reaction time. The conversion from monochloramine (NH2Cl) to dichloramine (NHCl2) is the major process involved, and either or both free chlorine and chloramines may be the major species present, depending on the Cl/N ratio. Model simulations showed that increasing the oxidant dose may not always enhance the performance of UV/chlor(am)ine in RO permeate, due to the need for a low free chlorine dose for optimal •OH exposure in RO permeate. Further UV/AOPs modelling showed that it is important to control the NH2Cl concentration to improve the UV/AOP performance in RO permeate, which may be achieved by extending the reaction time after chlorine is added or increasing the applied Cl/N ratio (e.g., increasing chlorine dose). However, these measures only enhance the pollutant percentage removal by about 5 % under the conditions modelled. A simulation tool was developed and is provided to predict the speciation of chlor(am)ine in RO permeate.

Comparison of the yields of mono-, Di- and tri-chlorinated HAAs and THMs in chlorination and chloramination based on experimental and quantum-chemical data

Thermodynamic and kinetic aspects of the formation of trihalomethanes and haloacetic acids determined based on the quantum chemical (QC) simulations were compared in this study with the experimental data generated using the differential spectroscopy approach in chlorination and chloramination. The ratios of the slopes of the correlations between -DlnA350 values and individual DBPs concentrations (SNH2Cl/SHOCl) were observed to be linearly correlated with the ratios of the Gibbs free energies (ΔGNH2Cl/ΔGHOCl) of the corresponding reactions of chloramine and chlorine with acetaldehyde which was used as a model DBP precursor in QC simulations. Further QC examination of the kinetics of chlorination and chloramination of the model compound acetoacetic acid showed that the activation energy of reactions between monochloramine that directly participates in substitution reactions to form mono-, di and tri-halogenated intermediates are 2–3 times higher than those of HOCl formed via the hydrolysis monochloramine. This result confirms that the interactions of chloramine with NOM and ensuing DBP formation are primarily mediated by the free chlorine released as a result of the hydrolysis of monochloramine while direct halogenation of NOM by monochloramine is likely to provide a small contribution to DBP formation.

Effect of disinfection processes and anthropogenic pollutants on comparative formation of trihalomethanes and N-nitrosodimethylamine

Chloramination and chlorination contribute to the formation of N-nitrosodimethylamine and trihalomethanes, respectively, both of which are defined as disinfection by-products. To be able to select the most appropriate water treatment scheme, it is important to comparatively evaluate the formation of both of these disinfection by-products during the application of different disinfection methods. In this study, chlorination, chloramination and stepwise chloramination methods have been applied to surface water samples that have been spiked with known N-nitrosodimethylamine precursors. Experimental results showed that ranitidine can be an effective N-nitrosodimethylamine precursor in distilled water, when chloraminated with high concentrations (140 mg/L) for a long time (10 days), resulting in approximately 450 ng/L of N-nitrosodimethylamine. However, neither dimethylamine nor ranitidine leads to significant trihalomethanes or N-nitrosodimethylamine formation in lake water when chloramination is conducted with low concentration (2 mg/L) for 2 h. These results suggest that N-nitrosodimethylamine concentration measured in the effluent of the drinking water treatment plant may underestimate the N-nitrosodimethylamine concentration that will reach the consumers since chloramination reactions will continue in the distribution system. On the other hand, when only N-nitrosodimethylamine formation potential is used, it will overestimate the N-nitrosodimethylamine that might form in the distribution system due to high disinfectant concentration, high contact time and adjusted pH values used in the N-nitrosodimethylamine formation potential test.

Nitrosamines: A review of formation pathways, precursors, control, and occurrence in drinking water

Nitrogenous disinfection by-products (N-DBPs) are emerging by-products that may be present in drinking water as by-products of water treatment plant (WTP) operations. Nitrosamines are N-DBPs that form by reaction of chloramine with certain organic nitrogen-containing compounds; however, the exact processes and environments in which nitrosamines form are still not well understood. Organic nitrogen precursors react within the WTP and distribution system, forming the toxic by-products during chloramination, or while in distribution. To best control the formation potential of nitrosamines, precursors must be removed from source water prior to chloramine disinfection. These nitrosamine forming precursors are abundant in source waters worldwide, presenting a need for further study of the mechanisms that reduce the formation potential of nitrosamines in chloramination WTPs.

Characterization of iodinated disinfection by-products in chlorinated and chloraminated waters using Orbitrap based gas chromatography-mass spectrometry.

Recent developments in gas chromatography (GC)-mass spectrometry (MS) have opened up the possibility to use the high resolution-accurate mass (HRAM) Orbitrap mass analyzer to further characterize the volatile and semivolatile fractions of environmental samples. This work describes the utilization of GC Orbitrap MS technology to characterize iodine-containing disinfection by-products (iodo-DBPs) in chlorinated and chloraminated DBP mixture concentrates. These DBP mixtures were generated in lab-scale disinfection reactions using Llobregat river water and solutions containing Nordic Lake natural organic matter (NOM). The DBPs generated were concentrated using XAD resins, and extracts obtained were analyzed in full scan mode with the GC Orbitrap MS. Integration of high resolution accurate mass information and fragment rationalization allowed the characterization of up to 11 different iodo-DBPs in the water extracts analyzed, including one new iodo-DBP reported for the first time. Overall, formation of iodo-DBPs was enhanced during chloramination reactions. As expected, NOM characteristics and iodide and bromide content of the tested waters affected the amount and type of iodo-DBPs generated.

Thermodynamic properties of chloramine formation and related reactions during water treatment: A G4MP2, G4, and W1BD theoretical study

A high-level gas and aqueous phase theoretical thermodynamic study was conducted on the primary and related chemical reactions which occur during chloramination for water treatment using the G4MP2, G4, and W1BD composite methods with the SMD, PCM, and CPCM solvation models. The standard state (298.15 K, 1 atm or 1M) formation of mono-, di-, and tri-chloramines from their precursors via hypochlorous acid chlorination is substantially exothermic and exergonic in both the gas and aqueous phases. The excellent agreement between experimental and theoretical values for a range of structural and thermodynamic calculations on a suite of calibration compounds suggests that the G4MP2, G4, and W1BD calculations meet or exceed criteria for thermochemical accuracy. The temperature influence on the thermodynamics of chloramine formation is projected to be negligible regardless of phase between 0 and 100°C. Additional thermodynamic calculations were undertaken on associated chloramination reactions involving the disproportionation of monochloramine, the decomposition of di- and tri-chloramine, and the reactions of trichloramine with ammonia and dichloramine. The results from these investigations not only provide a better understanding of the reaction thermodynamics, they also allow for a more rigorous interpretation of proposed chloramination mechanisms.

Electrochemical disinfection of Escherichia coli in the presence and absence of primary sludge particulates

Electrochemical (EC) residual disinfection of Escherichia coli (E. coli) in the presence and absence of primary sludge particulates (PSPs) was studied. The kinetics followed a first-order rate law. When PSPs were absent, the EC residual disinfection rate coefficient (k) increased linearly with EC pretreatment energy (EC, 0–0.63 kWh/m3). However, with 143 mg PSPs/L, k first increased linearly with EC (0–0.28 kWh/m3) and then decreased linearly with EC (0.28–0.42 kWh/m3). H2O2 was detected during EC pretreatment in PSPs-free samples and the H2O2 concentration (CH) increased with EC (0–0.83 kWh/m3) linearly. Chloride was detected in PSPs aqueous samples (143 mg PSPs/L) and its concentration (CC) changed during EC pretreatment: initially, a decrease of CC was observed when EC increased from 0 to 0.28 kWh/m3, followed by an increase of CC when EC increased 0.28–0.42 kWh/m3. In both cases, k correlated to the initial post-EC chloride concentration (CCI) in an inverse linear relationship. This two-stage change of CC and k was caused by a combination of two reactions: anodic oxidation of chloride and the reaction of chloramines with excess chlorine. This paper explains the mechanisms underlying EC residual disinfection in the presence and absence of PSPs, and proposes a feasible strategy for EC disinfection when PSPs are present, an approach that could be useful in the treatment of combined sewage overflow (CSO).

Formation of free cyanide and cyanogen chloride from chloramination of publicly owned treatment works secondary effluent: laboratory study with model compounds.

The potential generation of cyanide species in wastewater upon chlorination in the presence of residual ammonia (resulting in chloramine formation) was investigated in experiments with synthetic solutions and publicly owned treatment works (POTW) secondary effluent. This study demonstrated that low concentrations (approximately 5 to 25 microg/L as cyanide) of cyanogen chloride (CNCI), a highly toxic cyanide species not measured in total or free cyanide analyses, could be detected as a result of chloramination reactions in POTW secondary effluent. The potential for chloramination of nitrogen-bearing organic compounds to yield CNCl and/or free cyanide was demonstrated in experiments with synthetic solutions spiked with selected precursor organics: L-serine, benzene, catechin, and humic acid. The amino acid L-serine yielded the largest concentrations of CNCI upon chloramination. Additionally, detectable cyanide (approximately 10 microg/L) was observed in solutions of L-serine and in POTW secondary effluent that was chloraminated followed by dechlorination to prevent destruction of any free cyanide produced. Thus, chlorination of POTW secondary effluent containing residual ammonia can lead to chloramination of organic compounds and the resulting production of CNCl and free cyanide.

Radiolytic Reactions of Monochloramine in Aqueous Solutions

30) L mol -1 cm -1 and 580 ) (56 ( 30) L mol -1 cm -1 . The ¥ NHCl radical undergoes self-decay and can react also with O2 to form a peroxyl radical. It is suggested that the peroxyl radical exists in equilibrium NHClO 2 ¥ / ¥ NHCl + O2 with an estimated equilibrium constant of (3 ( 2) 10 -3 mol L -1 . The reaction of chloramine with the carbonate radical is suggested to form a complex [CO3NH2Cl] ¥- with kf ) 2.5 10 5 L mol -1 s -1 and kr ) 4 10 2 s -1 , and this complex decomposes with k ) 7 10 2 s -1 to form ¥ NHCl.

Using a comprehensive model to identify the major mechanisms of chloramine decay in distribution systems

The principle mechanisms of chloramine residual decay in drinking water distribution systems is examined using a comprehensive model of chloramine reactions calibrated to distribution system data. The results reveal that four principle chloramine decay mechanisms must be considered, including: reactions with hypochlorous acid/ion (HOCl/OCl-); an auto- catalytic reaction in which chloramines spontaneously decay in the absence of other reactants; oxidation reactions with reduced forms of organics and iron; and biologically-catalyzed reactions, such as the reactions with nitrite produced by nitrifiers as well as the direct cometabolism of chloramines by nitrifiers. The chloramine reaction model fits the distribution system data best when all of these reactions, including cometabolism of chloramines by nitrifiers, are included in the model.

Gas phase reactions of NH 2Cl with anionic nucleophiles: nucleophilic substitution at neutral nitrogen

Reactions of chloramine, NH 2Cl, with HO −, RO − (R = CH 3, CH 3CH 2, CH 3CH 2CH 2, C 6H 5CH 2, CF 3CH 2), F −, HS −, and Cl − have been studied in the gas phase using the selected ion flow tube technique. Nucleophilic substitution ( S N 2) at nitrogen to form Cl − has been observed for all the nucleophiles. The reactions are faster than the corresponding S N 2 reactions of methyl chloride; the chloramine reactions take place at nearly every collision when the reaction is exothermic. The thermoneutral identity S N 2 reaction of NH 2Cl with Cl −, which occurs approximately once in every 100 collisions, is more than two orders of magnitude faster than the analogous reaction of CH 3Cl. The significantly enhanced S N 2 reactivity of NH 2Cl is consistent with a previous theoretical prediction that the barrier height for the S N 2 identity reaction at nitrogen is negative relative to the energy of the reactants, whereas this barrier height for reaction at carbon is positive. Competitive proton abstraction to form NHCl − has also been observed with more highly basic anions (HO −, CH 3O −, and CH 3CH 2O −), and this is the major reaction channel for HO − and CH 3O −. Acidity bracketing determines the heat of deprotonation of NH 2Cl as 374.4 ± 3.0 kcal mol −1.

On-line monitoring of chloramine reactions by membrane introduction mass spectrometry

Membrane introduction mass spectrometry has been applied to on-line monitoring of the reaction of monochloramine with hydrogen chloride. The detection limit for monochloramine introduced by a sheet-membrane direct-insertion probe and measured by electron impact ionization and selected ion detection was found to be 0.7 mg/l. Formation of dichloramine, trichloramine and molecular chlorine in response to the addition of hydrogen chloride to the monochloramine solution was measured on-line. The flow-through membrane introduction mass spectrometry method for detection of chloramines and characterization of their chemistry has minimal memory effects, high molecular specificity, high speed of analysis owing to fast response times, and low detection limits.

Reactions of chloramine with methylpyridines. Synthesis and crystal structure of N-amino-3,5-dimethylpyridinium chloride

The reactions of 2,4-, 2,3-, and 3,5-lutidines and 2,4,6-collidine with ether solutions of chloramine were examined. Only in the case of 3,5-lutidine was an amination product obtained. In the other cases ammonium chloride and the hydrochlorides of the respective nitrogen bases were the only solids isolated. The crystal structures of the amination product was determined by X-ray diffraction and shown to be N-amino-3,5-dimethylpyridinium chloride, C 7 H 11 N 2 Cl. Crystals are triclinic, space group P1

Synthesis of dialkyltriazanium chlorides through chloramination reactions of dialkylamines

The chloramination of some alkyl- and dialkylamines was carried out, and the products were analyzed by infrared spectroscopy, mass spectroscopy, and nuclear magnetic resonance spectroscopy. The results show that (1) chloramine reacts with isopropylamine to give, among other products, isopropyltriazane trihydrochloride, (2) chloramine reacts with diisopropylamine to give 2,2-diisopropyltriazanium chloride, and (3) chloramine reacts with dibenzylamine to give 2,2-dibenzyltriazanium chloride

Synthesis of acetylhydrazines through chloramination reactions of amides and urethanes

The reactions of chloramine with the sodium salts of some amides and N-alkylurethanes have been carried out. The products were analyzed by infrared spectroscopy, mass spectroscopy, and nuclear magnetic resonance spectroscopy. It was shown that chloramine reacts with the sodium salts of phenyl and aromatic amides such as acetanilide and N-benzoylbenzamide to give acetylphenylhydrazine and acetylarylhydrazines, respectively, reacts with the sodium salts of aliphatic carboxamides such as N-methylacetamide to give the corresponding acetylhydrazine, and reacts with the sodium salts of N-alkylurethanes such as N-ethylurethane to give 1-(ethoxycarbonyl)-1-alkylhydrazine

Nonmetal redox kinetics: general-acid-assisted reactions of chloramine with sulfite and hydrogen sulfite

Cinetique de la reaction. Le ClSO 3 − forme s'hydrolyse rapidement pour donner SO 4 2− et Cl − . La reaction de NH 2 Cl avec SHO 3 − est egalement assistee par les acides

Reactions du n=chloroparatoluenesulfonamidate de sodium (chloramine t) sur les olefines en miliu acide organique

Vic. chloro-acetoxy and vic. chloro-tosylamino alcanes are the main products of the electrophilic reaction of chloramine T on olefins in acetic acid. The stereochemistry of the acetoxy chloration of the 2-butenes and cyclohexene is trans.

A Review of: “CHLORAMINATION REACTIONS. Edited by Stephen E. Frazier and Harry H. Sisler, Benchmark Papers in Inorganic Chemistry, Vol. 6, ed. H. H. Sisler, Dowden, Hutchinson and Ross, Inc., 1977, xii + 288 pp. $28.00”

A Review of: “CHLORAMINATION REACTIONS. Edited by Stephen E. Frazier and Harry H. Sisler, Benchmark Papers in Inorganic Chemistry, Vol. 6, ed. H. H. Sisler, Dowden, Hutchinson and Ross, Inc., 1977, xii + 288 pp. $28.00”