CCl Bond Research Articles

Modeling 3D-CSIA data: Carbon, chlorine, and hydrogen isotope fractionation during reductive dechlorination of TCE to ethene

Reactive transport modeling of multi-element, compound-specific isotope analysis (CSIA) data has great potential to quantify sequential microbial reductive dechlorination (SRD) and alternative pathways such as oxidation, in support of remediation of chlorinated solvents in groundwater. As a key step towards this goal, a model was developed that simulates simultaneous carbon, chlorine, and hydrogen isotope fractionation during SRD of trichloroethene, via cis-1,2-dichloroethene (and trans-DCE as minor pathway), and vinyl chloride to ethene, following Monod kinetics. A simple correction term for individual isotope/isotopologue rates avoided multi-element isotopologue modeling. The model was successfully validated with data from a mixed culture Dehalococcoides microcosm. Simulation of Cl-CSIA required incorporation of secondary kinetic isotope effects (SKIEs). Assuming a limited degree of intramolecular heterogeneity of δ37Cl in TCE decreased the magnitudes of SKIEs required at the non-reacting Cl positions, without compromising the goodness of model fit, whereas a good fit of a model involving intramolecular CCl bond competition required an unlikely degree of intramolecular heterogeneity. Simulation of H-CSIA required SKIEs in H atoms originally present in the reacting compounds, especially for TCE, together with imprints of strongly depleted δ2H during protonation in the products. Scenario modeling illustrates the potential of H-CSIA for source apportionment.

Selective reduction of a C[sbnd]Cl bond in halomethanes with Et3GeH at nanoscopic Lewis acidic Aluminium fluoride

The selective activation of CCl bonds of hydrochlorofluoromethanes and chloromethanes at moderate reaction conditions using ACF in a combination with Et3GeH is presented. The reactions of the chloromethanes (CH3Cl, CH2Cl2, CHCl3 and CCl4) in the presence of Et3GeH and ACF as catalyst led to the activation of only one CCl bond resulting in the hydrodechlorination. Friedel-Crafts reactions with benzene as solvent are suppressed by Et3GeH. A selective hydrodechlorination of hydrochlorofluoromethanes was achieved, because a transformation of a CF bond into a CH bond by the combination of ACF with Et3GeH did not occur. Supporting PulseTA® experiments illustrated the interaction between the solid catalyst and Et3GeH, the solvent benzene or CH2Cl2.

C[sbnd]Cl bond activation with Pd(II)-NiO nanoparticles supported on zeolite-Y: The role of charge transfer transition

Well dispersed Pd-NiO nanoparticles (Pd-NiO NP’s) formed over zeolite-NaY was found to be highly efficient catalyst for the Suzuki-Miyaura cross-coupling reaction of aryl chlorides and phenylboronic acid derivatives. Exceptional CC coupling products up to 92% were obtained within short period of time with chlorobenzene and their derivatives under microwave irradiation. Cyclic voltammetry (CV) study predicted that the leached Pd-NiO species were the “true catalyst” in the CCl bond activation process. Insitu generation of active Pd(0) via a charge transfer transition from NiO→Pd(II) was confirmed from CV study and was believed to be the crucial step in CCl bond activation. Filtration and CV analysis suggested for quick re-deposition of Pd-NiO NP’s on zeolite-NaY surface and confirmed for the non-consumption of Ni(OH)2 species.

Degradation kinetics and pathways of haloacetonitriles by the UV/persulfate process

Haloacetonitriles (HANs) are the most frequently found nitrogenous disinfection by-products (N-DBPs) in water. This study investigated the degradation of HANs, including dibromoacetonitrile (DBAN), monochloroacetonitrile (MCAN), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) in the UV/persulfate process. DBAN was efficiently degraded by the direct UV photolysis, while chlorinated HANs (CANs) were more efficiently degraded by the UV/persulfate process than by the UV or UV/H2O2 process. The degradation kinetics of MCAN, DCAN and TCAN by SO4− followed second order kinetics at the rate constants of 7.48 (±0.58)×107M−1·s−1, 6.36 (±0.16)×107M−1·s−1 and 2.43 (±0.15)×107M−1·s−1, respectively, which were 10 times higher than those by OH. The degradation rates increased with increasing persulfate dosages and temperatures, but were suppressed by natural organic matter and bicarbonate. The degradation of CANs in the UV/persulfate process was initiated by hydrogen abstraction and CC bond breakage by SO4− instead of CCl bond cleavage, and followed by subsequent oxidation and hydrolysis to produce Cl−, NO3−, CO2 and H2O. This study demonstrates that SO4− is more suitable than OH for the degradation of CANs, but the effective dehalogenation of aliphatic halogenated compounds by SO4− still requires at least one hydrogen or carbon atom connecting to an alpha carbon.

Ultrafast photochemistry with two product channels: Wavepacket motion through two distinct conical intersections

Light induced bond cleavage is an ubiquitous process in large molecules, yet its quantum nature is not fully understood. We present a comprehensive description of the ultrafast light induced CCl bond cleavage in diarylmethyl chlorides combining femtosecond transient absorption measurements with ab initio calculations. We observe a delayed appearance of radicals (80fs) and cations (125fs). The excited state wavepacket moves initially toward two conical intersections and the passing through these intersections determines the partitioning into the differing product channels. Different locations of the conical intersections explain the observed delay times.

Ruthenium complexes bearing a tridentate polypyridyl ligand with non-coordinating donor atoms: Construction of a specific coordination environment involving noncovalent interactions

We have prepared carbonyl (CO) ruthenium complexes which contained the tridentate polypyridyl type ligand (2,6-di(1,8-naphthyridin-2-yl)pyridine; dnp) with non-coordinating nitrogen atoms, for the development of specific reactions using noncovalent interactions. Similar to the aqua precursors that display intramolecular hydrogen bonds between the aqua and dnp ligands, a noncovalent interaction is formed between the terminal carbonyl ligand and non-coordinating nitrogen atoms of dnp; its strength depends on the identity of the axial ligand (triphenylphosphine or pyridine). Additionally, we investigated the reactivity of dnp-containing complexes bearing carbonyl ligands in both the equatorial and axial positions. As a result, it is suggested that the noncovalent interaction between dnp and CO ligands in positions equatorial to the dnp ligand is relatively strong, because the axial carbonyl ligand dissociates preferentially in ligand substitution reactions using organic solvents. Furthermore, in the ligand substitution reaction with a nitrile derivative, the coordination space constructed by the {Ru-dnp}2+ unit enables regulation of not only the ligand substitution reaction rate but also the identity of the donor atom. The present complex also leads to activation and cleavage of inert CCl and CBr bonds.

Dissociative photoionization of 1,2-dichloroethane in intense near-infrared femtosecond laser field

We experimentally demonstrate the dissociative photoionization of 1,2-C2H4Cl2 molecules in femtosecond laser field by time-of-flight mass spectrum and dc-slice imaging technology. Our results show the low kinetic energy components are from the dissociative ionization process of singly charged molecular ions, and the positive charge assignment are greatly influenced by the appearance energy of the fragment ions. The high kinetic energy components result from Coulomb explosion of multi-charged molecular ions, and the different angular distribution of these fragments along CC and CCl bond dissociation can be explained by the potential energy surfaces of the molecular ions.

Simulating stable carbon and chlorine isotope ratios in dissolved chlorinated groundwater pollutants with BIOCHLOR-ISO

BIOCHLOR is a well-known simple tool for evaluating the transport of dissolved chlorinated solvents in groundwater, ideal for rapid screening and teaching. This work extends the BIOCHLOR model for the calculation of stable isotope ratios of carbon and chlorine isotopes in chloroethenes. An exact solution for the three-dimensional reactive transport of a chain of degrading compounds including sorption is provided in a spreadsheet and applied for modeling the transport of individual isotopes 12C, 13C, 35Cl, 37Cl from a constant source. The model can consider secondary isotope effects that can occur in the breaking of CCl bonds. The model is correctly reproducing results for δ13C and δ37Cl modeled by a previously published 1-D numerical model without secondary isotope effects, and is also reproducing results from a microcosm experiment with secondary chlorine isotope effects. Two applications of the model using field data from literature are further given and discussed. The new BIOCHLOR-ISO model is distributed as a spreadsheet (MS EXCEL) along with this publication.

Ionic Liquid Induced Enhancement in the Stickiness of Sticky Dissociative Electroreductive C[sbnd]Cl Bond Cleavage: A Key to Eco-Green Detoxification of Chloroacetonitrile

Detailed voltammetric investigations that demonstrate the potential of 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]), a commonly used room-temperature ionic liquid (RTIL), to enhance the stickiness in the sticky dissociative electrodetoxification pathway for chloroacetonitrile are presented. Convolution analysis of the voltammetric data in light of the Marcus-Hush formulation reveals that electroreductive cleavage of the CCl bond of chloroacetonitrile (ClCH2CN) in [BMIM][BF4] follows a sticky dissociative pathway like that in conventional organic solvents. Interestingly the interaction energy between Cl̄ and CNCH2 (radical) in [BMIM][BF4] is observed to be almost ten times higher than that reported for the same species in N,N-dimethylformamide (DMF). This RTIL-induced enhancement in the interaction energy among the electrochemically generated fragments reduces the kinetic barrier and hence the overpotential required for heterogeneous electroreduction of ClCH2CN. The lower overpotential that implies lesser energy consumption for the electroreduction and the green features of [BMIM][BF4] jointly support the use of imidazolium-based RTILs for eco-green electrodetoxification of halohydrocarbons like chloroacetonitrile.

Degradation products of profenofos as identified by high-field FTICR mass spectrometry: Isotopic fine structure approach

ABSTRACTThis study was performed to identify the degradation products of profenofos “a phenyl organothiophosphate insecticide” in raw water (RW) collected from the entry point of Metropolitan Water Works Authority “Bangkaen, Thailand” and ultrapure water (UPW) with and without TiO2 under simulated sunlight irradiation. Degradation of profenofos was followed with ultrahigh performance liquid chromatography (UHPLC) and follows pseudo first-order kinetic. Accordingly, high-field FTICR mass spectrometry coupled to an electrospray ionization source was used to reveal the degradation routes of profenofos and the isotopic fine structures (IFS) elucidations to approve the chemical structures of its degradation products. More degradation products were detected in UPW as compared to RW. Consequently, two main degradation pathways namely (i) interactive replacements of bromine and hydrogen by hydroxyl functional groups and (ii) rupture of PO, PS, CBr and CCl bonds were observed. None interactive replacement of chlorine by hydroxyl functional group was detected. Accordingly, mechanistical pathways of the main degradation products were established.

Kinetics of the gas-phase thermal decomposition of 3-chloropropene

The pyrolysis of 3-Chloropropene was studied in a static system in the temperature range 683–750K and pressure 45–92Torr. For the overall reaction the Arrhenius parameters were observed as, Ea=183.2±5.6kJmol−1, and log10 (A, s−1)=9.49±0.41. Two mechanisms, dehydrochlorination molecular elimination and CCl bond fission are discussed in detail. To interpret the fall-off behaviour, RRKM/ME calculations were adopted and the pressure dependent rate constants were calculated at collision efficiency of 0.5. From the pressure dependence study and RRKM calculations, it can be concluded that we are at the high-pressure limit.

Mechanism of reaction CH3COCl with HNO: A theoretical study

The mechanism of the reaction of CH3COCl with HNO has never been investigated by theoretical and experimental methods before, which is explored in this contribution. The geometries are optimized at the BMK/6-311+G(d,p) level. On the basis of the optimized geometries, the energy is further refined at the BMC-CCSD level. Finally, twenty-five pathways and corresponding possible products are located including the cleavage of NH, CC, CH, and CCl bonds and formation of OH, OCl, ON, OC, NCl, NH, NC, HH, and HCl bonds. However, most of reaction pathways are impossible because of the higher barrier heights and positive reaction energy. The most favorable pathway is the NH1andCCl bonds rupture and H1Cl bond formation leading to products CH3CONO and HCl.

Effect of dual functional ionic liquids on the thermal degradation of poly(vinyl chloride)

The short-term thermal stability of PVC on addition of functional ionic liquids (ILs) based on phosphonium and pyridinium cations, and a docusate anion, was studied using FTIR, TGA-MS and TGA-FTIR. The thermal stability of PVC plasticized with these ILs is reduced and the activation energy for thermal degradation for the first step of PVC degradation lowered, relative to neat PVC. This feature is not dependent on the thermal stability of the IL itself, as their addition to neat PVC did not result in increased thermal stability of the resin. Analysis of the gases evolved during thermal degradation showed that there is no variation in the mechanism of PVC degradation in the presence of ILs, the only difference observed is that HCl is evolved at lower temperatures for PVC-ILs samples. The ILs had no effect on the second step of the thermal degradation of PVC. The decrease in the thermal stability of PVC-ILs is associated with two different effects: firstly, the anion weakens the CH bond while the cation forms complexes and weakens the CCl bond; second, the IL interaction with the polymer chains partly substitutes the interaction between the polymer chain and heat stabilizers (e.g. stearates) added to the PVC compound. In this way, the latter tends to be expelled from the bulk polymer, thus not being available for PVC stabilization at high temperature. Heat stabilizer migration is related to the solvating power of the ILs: the higher the solvating power, the higher the migration of heat stabilizer, the lower the thermal stability of the polymer.

Absorption and emission spectroscopic characteristics of dipterex and its molecularly imprinted recognition: A TD-DFT investigation

By using G09 program package, the absorption and fluorescence/phosphorescence spectra of dipterex were explored, and its spectroscopic characters were altered by methacrylic acid (MAA) as the imprinted molecule. The TD-DFT results revealed that: (1) All absorption and emission excitations of dipterex are assigned to the nσ∗ transition; (2) without MAA as imprinted molecule, one of the dipterex CCl bonds is extended significantly and dipterex is almost destroyed in transition states; (3) dipterex is connected to methacrylic acid via two hydrogen bonds; (4) for the dipterex–MAA complex, the electronic excitation (ππ∗ excitation) in absorption spectra is dominated by the configuration HOMO→LUMO.

Ab initio molecular dynamics simulation study of dissociative electron attachment to C6H5(CH2)nCl (n = 0, 1, 2, 3, 4)

The CCl bond cleavages induced by electron attachment to 1-chloroalkyl benzenes [C6H5(CH2)nCl, n=0, 1, 2, 3, 4] are investigated with ab initio molecular dynamics simulations. The fragment Cl− is generated and the CCl bond cleavage time decreases with the increasing length of the alkyl chain. In the dissociative electron attachment processes, the incoming electron is initially captured to the local π* virtual orbital of the phenyl group and then transfers to the anti-bond σ* orbital of the remote CCl moiety; the variation of the CCl bond cleavage times shows a similar trend of the dissociation thresholds of C6H5(CH2)nCl+e−→C6H5(CH2)n+Cl−.

Multi-photon dissociation dynamics of Freon 1110 induced by femtosecond laser pulse

The ozone layer which absorbs harmful solar UV radiation is an essential umbrella for human beings. However, a large number of exhausts of chlorine compounds including freon released by people in the atmosphere pose a great threat to the ozone layer. Freon dissociates into the product of chlorine radicals induced by UV sunlight radiation, which are found to be the main culprit for the destruction of atmospheric ozone. In this paper, time-of-flight mass spectrometry and velocity map imaging technique are coupled for investigating the multiphoton dissociation dynamics of Freon 1110 (C2Cl4, Tetrachloroethylene) induced by ultrafast short laser pulse on a femtosecond time scale at 800 nm. Fragments mass spectra of C2Cl4 are measured by time-of-flight mass spectrometry. Together with the parent ion C2Cl4+, two dominant fragment ions C2Cl3+ and C2Cl2+ are discovered in the multi-photon ionization and dissociation process in the experiment. By analyzing the above mass spectra, two corresponding photodissociation mechanisms are discussed and listed as follows: 1) C2Cl4+C2Cl3+ +Cl with single CCl bond breaking and direct production of Cl radical; 2) C2Cl4+C2Cl2+ +2Cl with double CCl bonds breaking and production of two Cl radicals. Also, ion images of these two observed fragment ions C2Cl3+ and C2Cl2+ are measured by velocity map imaging apparatus. The kinetic energy distributions of these two fragment ions are determined from the measured velocity map images. The kinetic energy distributions of both C2Cl3+ and C2Cl2+ can be well fitted by two Gaussion distributions. It indicates that both fragments C2Cl3+ and C2Cl2+ are from two production channels. The peak energies for each channel are fitted. More detailed photodissociation dynamics is obtained by analyzing the angular distribution of the generated fragment ions. The anisotropy parameter values are measured to be 0.46 (low energy channel) and 0.52 (high energy channel) for the fragment C2Cl3+, and 0.41 (low energy channel) and 0.66 (high energy channel) for the fragment C2Cl2+, respectively. The ratios between parallel transition and perpendicular transition are determined for all the observed channels for producing fragments C2Cl3+ and C2Cl2+. In addition, density functional theory calculations at a high-precision level are also performed on photodissociation dynamics for further analysis and discussion. The optimized geometries of ground state and ionic state of C2Cl4 are obtained and compared with density functional theory calculation at the level of B3LYP/6-311G++(d,p). The different structures of the ground and ionic states are given and discussed. The calculated information about ionic states of C2Cl4, including energy level and oscillator strength for the ionic excited states, is also given for analyzing the photodissociation dynamics of the C2Cl4 ions.

Polyvinyl chloride degradation by hybrid (chemical and biological) modification

Chemical and microbial modifications are not common with polyvinyl chloride (PVC). This paper presents a novel green hybrid technique for the PVC degradation using biodegradation followed by chemical modification, using glycerol and urea (C-PVC). Mucor rouxii specie is found to be susceptible towards C-PVC bio-degradation. Chemical change in PVC was monitored by observing change in the CC, CH and CCl bond environment using IR spectroscopy followed by dechlorination study. Role of ZnO in chemical modification was observed by elemental analysis. Thermogravimetric with IR study justified microbial participation in the degradation and found that M. rouxii modified C-PVC (M-PVC) considerably reduces degradation time and temperature. Degradation temperature for C-PVC and M-PVC was noted as 550 °C and 450 °C, as compared with PVC 600 °C. Degradation pattern was also investigated by surface morphological using AFM analysis.

Catalytic total oxidation of 1,2-dichloroethane over VOx/CeO2 catalysts: Further insights via isotopic tracer techniques

Catalytic total oxidation of 1,2-dichloroethane (DCE) on CeO2 and VOx/CeO2 catalysts is investigated via various isotopic tracer techniques, including kinetic isotope effect (KIEs) measurements, in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFT) of deuterated 1,2-dichloroethane oxidation, H/D exchange of surface hydroxyl groups, temperature-programmed isotopic exchange (TPIE) and 18O2 isotope labeling experiments. The activation and dissociation of CCl bonds is determined to be the first step of DCE oxidation, and oxygen vacancies are identified as the main active sites by KIEs and density functional theory (DFT) calculations. For VOx/CeO2 catalysts, surface lattice oxygen is found to directly involve in oxidation of DCE via the formation of intermediate species of partial oxidation such as aldehyde species or CO, which are then totally oxidized into CO2 by the surface peroxide species. The occurrence of HCl is attributed to the reaction of surface hydroxyl groups with the dissociated Cl adsorbed on oxygen vacancies, whereas the rapid replenishment of the consumed OH is crucial for maintaining a better stability.

ELECTROCHEMICAL REDUCTION OF BENZYL CHLORIDE ON SILVER, GRAPHITE AND SILVER/GRAPHITE POWDER MACROELECTRODES

Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, graphite or silver/graphite mixtures (1:3, 1:1 and 3:1) in absence of solvent, or using a very low amount of DMF as solvent (PhCH2Cl/DMF 3:1). A 0.1molL−1 KCl aqueous solution was used as anolyte. A competitive hydrogenation and dimerization process was observed, affording the respective toluene and bibenzyl products. The well-known electrocatalytic effect of silver on reduction of the CCl bond was confirmed by a significant positive shift of the benzyl chloride reduction potential in comparison with pure graphite powder. The products distribution was analysed after linear sweep voltammetries at low scan rate (0.1mVs−1), indicating high yields of bibenzyl produced on Ag/graphite-PME. Pure graphite-PME was not selective towards dimer formation. The best results for bibenzyl production occurred at more positive potentials, in the presence of silver. A small amount of solvent (DMF) play an important role on the electrode surface desorption and diffusion of intermediary species.

Detailed kinetics of methylphenyldichlorosilane synthesis from methyldichlorosilane and chlorobenzene by gas phase condensation

Methylphenyldichlorosilane (MPDS, CH3C6H5SiCl2) is an important silicone monomer for the synthesis of high-performance polymethylphenylsiloxane polymers. In this work, the mechanism of the synthesis of MPDS from methyldichlorosilane and chlorobenzene by gas phase condensation was studied, and a kinetic model with 35 species and 58 elementary reactions was established. Experiments were carried out in a tubular reactor under a wide range of reaction conditions. The calculated mole fractions of the reactants and products were in a good agreement with the experimental results. A mechanism of the insertion of chloromethylsilylene into the CCl bond of chlorobenzene was proposed, which was proved to be the main pathway of MPDS production. The established kinetic model can be used in design and optimization of the industrial reactor for MPDS synthesis.