Dichloroethylene Isomers Research Articles

General analytical solutions of multispecies advective-dispersive solute transport equations coupled with a complex reaction network

Stepwise reductive dechlorination of tetrachloroethene (PCE) to trichloroethene (TCE), three dichloroethylene (DCE) isomers (1,1-DCE, cis −1,2- DCE, and trans −1,2- DCE), vinyl chloride (VC), and ethane (ETH) may proceed under anaerobic conditions. However, most multispecies transport models for describing the plume migration of a chemical mixture comprising the original chlorinated solvent and its dechlorinated byproducts in the literature are often simplified to a sequential first-order reaction network which cannot account for the divergent reactions from TCE to the three DCE isomers and convergent reactions from the three DCE isomers to VC. In this study, general analytical solutions to multispecies transport equations with a complex reaction network were derived for a combination of semi-infinite and finite systems. The developed analytical solutions were robustly verified against a semi-analytical solution that can consider the same complex reaction network. The verification results indicated that the derived analytical solutions were accurate and robust. The general solutions derived in the present study were also used to investigate the effects of the outlet boundary conditions on solute transport involving a complex reaction network. The results showed that the analytical solution derived for infinite outlet BCs predicted lower concentrations of contaminants near the outlet boundary than those for finite outlet BCs. Moreover, a straight decay chain model may over- or under- estimate the DCE and VC concentrations compared to the multiple branching isomer reaction model. The developed analytical solutions with a complex reaction network provide more realistic and efficient tools for assessing the movement of chlorinated solvents and their degradation-related byproducts in soil–water systems.

Mass-Resolved Momentum Imaging of Three Dichloroethylene Isomers by Femtosecond Laser-Induced Coulomb Explosion

Coulomb explosion experiments using linearly polarized intense 60 fs laser pulses were conducted for structural characterization of three dichloroethylene (DCE) isomers, 1,1-DCE, cis-1,2-DCE, and trans-1,2-DCE. Under relatively low laser intensity at 1.8 × 1014 W/cm2, mass-resolved momentum imaging (MRMI) for selected fragment ions of 35Cl+ and C2+ revealed different patterns for the three isomers. The C2+ ion fragmented from multiply charged trans-1,2-DCE was forced to leave perpendicularly to the direction of the laser polarization, due to recoil forces from adjacent cations. In contrast, the fast ions of C2+ from cis-1,2-DCE exhibited an isotropic distribution, whereas the fast ions of C2+ from 1,1-DCE recoiled along the laser polarization together with the slow C2+ ions, and thereby distinction of the three isomers was demonstrated. Coulomb explosion occurs predominantly at specific orientation, which is useful for potential applications of MRMI analysis to molecular structure assays.

Investigation of the isomerism of dichloroethylene in momentum space

The geometric parameters are optimized at the B3LYP and CI levels under the constraints of the C2v, C2v and C2h symmetry point groups for the three isomers of dichloroethylene. The theoretical two-dimensional electron momentum distributions and momentum profiles of four core orbitals for iso-dichloroethylene, cis-dichloroethylene and trans-dichloroethylene are calculated by non-relativistic density functional method. Comparing the electron distributions in position and momentum space of these orbitals, it is found that the interference effects, which do not exit in position space, appear and produce the evident periodical multipeaked momentum distributions in momentum space. The distances between atoms and the alignments of molecular axes for these three isomers can be obtained by computing their values of period and the axis directions of period, respectively.

Transformation of Trichloroethylene to Predominantly Non‐Regulated Products under Stimulated Sulfate Reducing Conditions

AbstractAnaerobic microcosms containing sediment and water were amended to generate a range of mass loadings of FeS. Microcosms were then spiked with trichloroethylene (TCE) and the concentration of TCE and possible volatile reaction products monitored over time. The lowest yields of TCE, as well as the lowest yields of reaction products regulated under the Safe Drinking Water Act (i.e., dichloroethylene isomers and vinyl chloride), were observed at FeS mass loadings at or above 20 g/L. Sixty eight days after spiking with TCE, selected microcosms were amended with sulfate and lactate, or sulfate, Fe(II), and lactate, and the effect of these amendments on TCE transformation and yield of regulated products was compared to microcosms that did not receive any amendments. Addition of sulfate, Fe(II), and lactate led to the greatest improvement on TCE depletion rates and the lowest yields of regulated reaction products compared with addition of sulfate and lactate, or no amendments. Analysis of kinetic modeling suggests that microbial and abiotic processes acted in concert to promote TCE transformation to a relatively low yield of regulated products in microbially active microcosms that contained high mass loadings of FeS.

Effect of the Cl2p core orbital excitation on the nuclear dynamics of the three dichloroethylene isomers

In this article, we present the X-ray absorption spectra of the three isomers of dichloroethylene C2H2Cl2 in the vicinity of the chlorine L2 and L3 edges. These isomers were excited along the first Cl2p to lowest unoccupied molecular orbital transition and an analysis of the corresponding resonant Auger spectra shows that the C–Cl bond can break before the electronic decay. An investigation of a possible Auger Doppler-like effect is also presented.

Morpho butterfly wing scales demonstrate highly selective vapour response

Tropical Morpho butterflies are famous for their brilliant iridescent colours, which arise from ordered arrays of scales on their wings. Here we show that the iridescent scales of the Morpho sulkowskyi butterfly give a different optical response to different individual vapours, and that this optical response dramatically outperforms that of existing nano-engineered photonic sensors. The reflectance spectra of the scales provide information about the nature and concentration of the vapours, allowing us to identify a range of closely related vapours–water, methanol, ethanol and isomers of dichloroethylene when they are analysed individually. By comparing the reflectance as a function of time for different vapours, we deduce that wing regions with scale structures of differing spatial periodicity give contributions to the overall spectral response at different wavelengths. Our optical model explains the effect of different components of the wing scales on the vapour response, and could steer the design of new man-made optical gas sensors.

Identification and Characterization of the Chemotactic Transducer in Pseudomonas aeruginosa PAO1 for Positive Chemotaxis to Trichloroethylene

Pseudomonas aeruginosa PAO1 is repelled by trichloroethylene (TCE), and the methyl-accepting chemotaxis proteins PctA, PctB, and PctC serve as the major chemoreceptors for negative chemotaxis to TCE. In this study, we found that the pctABC triple mutant of P. aeruginosa PAO1 was attracted by TCE. Chemotaxis assays of a set of mutants containing deletions in 26 potential mcp genes revealed that mcpA (PA0180) is the chemoreceptor for positive chemotaxis to TCE. McpA also detects tetrachloroethylene and dichloroethylene isomers as attractants.

Formation of vinylidene and vinylene by selective reactivity of Si(1 0 0)2 × 1 towards iso, cis and trans isomers of dichloroethylene

The room temperature (RT) chemisorption of three ( iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-σ bonded 2-chlorovinyl and di-σ bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom π-complex and diradical intermediates, respectively. Acetylene ( m/ z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl 2 group favours the diradical dechlorination mechanism. The single m/ z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies.

Dual-response resonant chemical sensors for multianalyte analysis

We developed an approach to increase the information content from resonant, thickness-shear mode (TSM) sensors. These sensors are intended for integration into a microanalytical system that will periodically collect and precondition a predetermined volume of sample and will further present it to the sensor for analysis. Each side of the TSM resonator is coated with a different sensor film. During measurements, only one side at a time is exposed to an analyzed vapor while another side is exposed to a blank gas from a scrubber. Thus, analyte-related signals are generated independently from each side of the TSM sensor. Such dual-response sensing approach reduces the number of sensing elements by a factor of two, leading to further system miniaturization and improved power budget in sensor operation. We demonstrated our dual-response sensor concept with a high-performance, low noise TSM resonator ( f 0 = 10 7 Hz, RMS noise <0.05 Hz) arranged in a low volume (<200 μL) dual flow cell. With a single resonator, we successfully discriminated and quantified toxic industrial and environmental concern vapors such as toluene and trichloroethylene and two isomers of dichloroethylene (DCE) such as cis-1,2-DCE and trans-1,2-DCE.

Recognition and Quantification of Perchloroethylene, Trichloroethylene, Vinyl Chloride, and Three Isomers of Dichloroethylene Using Acoustic Wave Sensor Array

Recognition and Quantification of Perchloroethylene, Trichloroethylene, Vinyl Chloride, and Three Isomers of Dichloroethylene Using Acoustic Wave Sensor Array

Oxidation of chlorinated ethenes by potassium permanganate: a kinetics study

The kinetics of oxidation of perchloroethylene (PCE), trichloroethylene (TCE), three isomers of dichloroethylene (DCE) and vinyl chloride (VC) by potassium permanganate (KMnO 4) were studied in phosphate-buffered solutions of pH 7 and ionic strength ∼0.05 M and under isothermal, completely mixed and zero headspace conditions. Experimental results have shown that the reaction appears to be second order overall and first order individually with respect to both KMnO 4 and all chlorinated ethenes (CEs), except VC. The degradation of VC by KMnO 4 is a two-consecutive-step process. The second step, being the rate-limiting step, is of first order in VC and has an activation energy ( E a) of 7.9±1 kcal mol −1. The second order rate constants at 20°C are 0.035±0.004 M −1 s −1 (PCE), 0.80±0.12 M −1 s −1 (TCE), 1.52±0.05 M −1 s −1 ( cis-DCE), 2.1±0.2 M −1 s −1 (1,1-DCE) and 48.6±0.9 M −1 s −1 ( trans-DCE). The E a and entropy (Δ S ∗) of the reaction between KMnO 4 and CEs (except VC) are in the range of 5.8–9.3 kcal mol −1 and −33 to −36 kcal mol −1 K −1, respectively. Moreover, KMnO 4 is able to completely dechlorinate CEs, and the increase in acidity of the solution due to CE oxidation by KMnO 4 is directly proportional to the number of chlorine atoms in CEs.

GAS PHASE REDUCTION OF CHLORINATED VOCs BY ZERO VALENT IRON

The removal of trichloroethylene (TCE) by reduction with elemental iron was examined in batch reactors representing three phase gaseous systems (Fe0 (solid), water vapor + TCE vapor + air mixture (gaseous), and condensed water on Fe0 surface (aqueous)) and two phase aqueous systems (Fe0 (solid), water (aqueous)) as the reaction medium. Two separate removal mechanisms were found for TCE removal in the gas phase reactors: [1] adsorption onto the Fe0 surface under low relative humidity (RH), and [2] reaction with Fe0 to form other organic compounds, such as ethylene, isomers of dichloroethylene, and vinyl chloride under 100% RH conditions in the gas phase. The adsorption of TCE vapor onto the Fe0 surface was fast initially and highest at low temperatures. The reduction reaction of TCE in the gas phase was first order with respect to the TCE concentration remaining in the gas phase under conditions of 100% RH at 15, 22, and 35°C, and the observed reaction rate constant (k obs) exhibited a maximum at elevated temperatures. The estimated k obs values for the degradation of dissolved TCE in aqueous systems were the same order of magnitude with the rate constants in the gas phase and exhibited an increasing rate at higher temperatures. The results suggest that Fe0 represents an economical choice for vapor phase barriers to limit the spread of contaminants in soil gas and reduce fugitive air emissions from contaminated sites.

Intrinsic bioremediation of trichloroethylene and chlorobenzene: field and laboratory studies

Activities at a former fire training area at Robins Air Force Base in Georgia, USA resulted in contamination of groundwater with a mixture of trichloroethylene (TCE) and chlorobenzene (CB). Results from the field investigation suggest that intrinsic bioremediation process is occurring, which caused the decrease in TCE and CB concentrations, and increase in TCE degradation byproducts [e.g., dichloroethylene isomers (DCEs), vinyl chloride (VC)] concentrations. Contaminated groundwater samples collected from this site were used to conduct microbial enumeration tests, and used as the inocula for microcosm establishment. Results from the microbial enumeration study indicate that methanogenesis was the dominant biodegradation pattern within the source and mid-plume areas, and the aerobic biodegradation process dominated the downgradient area. Laboratory microcosm experiments were conducted to evaluate the feasibility of using CB as the primary substrate to enhance the intrinsic biodegradation of TCE. Microcosm results suggest that CB can serve as the primary substrate (electron donor), and enhance TCE biodegradation to less-chlorinated compounds under both aerobic cometabolism and reductive dechlorination conditions.

Translational energy distributions of the products of the 193 and 157 nm photodissociation of chloroethylenes

The 193 and 157 nm photodissociations of three isomers of dichloroethylene (DCE) and trichloroethylene (TCE) were investigated using a technique of photofragmentation translational spectroscopy. The photofragmentation mechanisms were constructed by analyzing the time-of-flight spectra of C2H2+, Cl+, HCl+, C2HCl+, and C2Cl2+ produced by electron impact of neutral photofragments. In the 193 nm photodissociation, both the HCl elimination and the C–Cl bond rupture were important for all the compounds examined. It was concluded that secondary dissociation of the vibrationally excited chlorinated vinyl radical produced by the C–Cl bond rupture was important even at 193 nm. In the 157 nm photodissociation, the mechanisms were similar to those at 193 nm for cis-DCE, 1,1-DCE, and TCE, while only the C–Cl bond rupture occurred for trans-DCE. This result suggests that the 157 nm photodissociation of trans-DCE proceeds via the direct photodissociation following the photoexcitation to the repulsive nσ*1 state. A minor C–H bond rupture was also found in the 157 nm photodissociations of cis-DCE and TCE. On the basis of the present mechanisms, the translational energy distributions and the branching ratios were estimated for all the possible processes.

State resolved translational energy distributions of Cl and HCl in the ultraviolet photodissociation of chloroethylenes

Velocity-aligned Doppler spectroscopy was used to measure the speed distribution functions of HCl(v″=0–2,J″) produced in the 193 nm photodissociation of vinyl chloride. A mechanism which is consistent with our present data as well with our earlier work is three center elimination of HCl followed by concerted but nonsynchronous isomerization of the vinylidene fragment, with some of the isomerization energy converted to kinetic energy of the recoiling fragments. In order to explain the vibrational dependence of the translational and rotational energy distributions, the mechanism is assumed to be vibrationally adiabatic. In addition, magic angle Doppler spectroscopy was used to measure the speed distribution functions of Cl atoms produced in the photodissociation of vinyl chloride and the three dichloroethylene isomers. Bimodal energy distributions were observed for both spin–orbit states, with the Cl(2P1/2) fragment having more kinetic energy than Cl(2P3/2). The data are consistent with competitive reaction on two potential energy surfaces. Adiabatic correlation, with some scrambling in the asymptotic region, provide a qualitative explanation of the spin–orbit branching ratios.

An ab initio study of many-body effects in the inner-valence region of cis-, trans-, and iso-dichloroethylene

Ab initio symmetry-adapted-cluster configuration-interaction calculations of the satellite structure inferred in the inner-valence region of the photoelectron spectra of all three dichloroethylene isomers are described. The results account for the splitting and mixing of the ionization channels and provide a detailed insight into the shake-up phenomena accompanying the primary hole configurations. A satisfactory reproduction of the general shape of the inner-valence spectral envelopes of dichloroethylene isomers is also obtained.

Field Evaluation of in Situ Aerobic Cometabolism of Trichloroethylene and Three Dichloroethylene Isomers Using Phenol and Toluene as the Primary Substrates

Download Hi-Res ImageDownload to MS-PowerPointCite This:Environ. Sci. Technol. 1995, 29, 6, 1628-1637

An ab initio molecular orbital study of the unimolecular dissociation reactions of di- and trichloroethylene

The potential energy surfaces for the unimolecular ground state elimination reactions of dichloroethylene (DCE) and trichloroethylene (TCE) are studied with ab initio molecular orbital calculations. By the gradient optimization with the second-order Mo/ller–Plesset perturbation (MP2) method and single point calculations with the fourth-order Mo/ller–Plesset perturbation (MP4) and the quadratic single and double configuration interaction including a triple contribution [QCISD(T)], many molecular elimination channels including three- and four-center HCl, H2, and Cl2 elimination and H and Cl migration reactions are systematically examined. For cis- and trans-DCE, the three-center HCl elimination with subsequent chlorovinylidene rearrangement has the lowest overall barrier, whereas for 1,1-DCE for which the three-center path is not available, the four-center elimination has a rather low barrier. Another path starting with the rearrangement of DCE isomers to 1,2-dichloroethylidene followed by HCl elimination is not far in energy from these paths, complicating the overall mechanism of HCl elimination. The H2 elimination from DCE isomers also can take either the three-center path or the 1,2-dichloroethylidene path. For TCE, though the overall barrier to produce HCl+dichloroacetylene is the lowest for the four-center HCl elimination pathway, the production of HCl itself is most easily accomplished by the three-center HCl elimination, and the easiest path for disappearance of TCE is its rearrangement via H or Cl migration to give the 1,2,2-trichloroethylidene intermediate. Thus the overall mechanism of HCl elimination reactions from TCE can also be complicated.

ChemInform Abstract: Distribution of Rotational States in Half‐Collisions: 193 nm Photolysis of Dichloroethylene Isomers.

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Distribution of rotational states in half-collisions: 193-nm photolysis of dichloroethylene isomers

The photodissociation of cis-, trans-, and 1,l -dichloroethylene (DCE) was studied by a pump-and-probe technique, using a 193-nm excimer laser to excite the parent molecule and time-of-flight resonance-enhanced multiphoton ionization to detect the products. We report here the nascent rotational state distributions of HCl(u”=O,1,2) and also the relative yields and intensity dependencies of HCl, H, CK2P3p), C1(2P1/2), HCP, and C1+. Our finding that the rotational state distributions of HCl for all three isomers are very similar leads us to conclude that the nascent distribution is determined far along the reaction coordinate and is insensitive to the isomeric form of the parent molecule, regardless of whether photoelimination results from a three- or four-center transition state. We also observed qualitatively different behavior for HCl(u”=O) and HCl(u”=1,2). As in our previous study of vinyl chloride, we found that HCl(u’30) has a Boltzmann-like rotational state distribution, with temperatures in this case near 1400 K, whereas the distribution for u” = 0 is described by a biexponential function with a low J” temperature around 300 K and a high J” temperature around 10 000 K. We propose that the dichotomy between these two distributions is due to microscopic rather than chemical branching. The relative yields of HCl and C1+ for trans-DCE are approximately double those of cis- and 1,l-DCE. This result is consistent with the interpretation that the yield-determining step is faster than cis-trans isomerization. The yields of all the other products are the same for cis and trans. For 1,l-DCE the yields of H, Cl(*P1p), and HCl+ are much greater than for cis- and trans-DCE, while for C1(2P3p) the 1 ,1-DCE yield is somewhat smaller. The relative yields of H and C1(2P3p) can be explained by the stabilities of the organic fragments, while the HCl+ yields can be explained statistically. All of the neutral fragments were found to be produced by singlephoton processes, while HCl+ and Cl+ require three and four photons, respectively. Ladder climbing mechanisms are proposed for the two ionic fragments.