CCl Bond Research Articles

TiO2 photocatalytic degradation and transformation of oxazaphosphorine drugs in an aqueous environment

This study investigated the TiO2 photocatalytic degradation and transformation of the oxazaphosphorines ifosfamide (IFO), cyclophosphamide (CP) and trofosfamide (TRO). Under the optimum conditions of TiO2=100mg/L, IFO=100μg/L and solution pH=5.5, IFO was completely removed within 10min (k=0.433min−1). The results indicated that OHfree radicals generated by valence holes in the bulk solution were the predominant species for the degradation of IFO. At higher initial concentrations of oxazaphosphorines (20mg/L), >50% of TOC remained after 6h of reaction time, indicating that parent compounds were transformed to byproducts, which exhibit higher Microtox acute toxicities; chlorinated byproducts were likely the source of toxicity. Photocatalytic degradation pathways of the three oxazaphosphorines were proposed. IFO, CP and TRO follow very similar pathways and bond-breaking processes: ketonization and breaking of the CCl bond, the PN bond and the CN bond (N-dechloroethylation). Chloride (Cl−) release is likely the first and primary step in the decomposition process. Several of the identified byproducts were also metabolites, which implies that photocatalytic oxidation proceeds through pathways that are similar to metabolic pathways.

Sensitive determination of chlorpyrifos using Ag/Cu alloy nanoparticles and graphene composite paste electrode

A novel Ag/Cu alloy nanoparticles and graphene nanocomposite paste electrode was fabricated and its electrochemical activity was investigated using cyclic voltammetry and electrochemical impedance studies. Electrochemical reduction of chlorpyrifos using the nanocomposite produced peak signal based on 2e− reductive cleavage of CCl bond in trichloropyridine moiety. Increase in peak currents and decrease in overpotential for chlorpyrifos was observed for Ag/Cu–graphene nanocomposite compared to Ag–graphene, Cu–graphene, graphene paste and carbon paste electrodes. This could be attributed to the synergistic combination of graphene and Ag/Cu alloy nanoparticles with good adsorption, large surface area, increased active sites leading to fast electron transfer rates and high electrical conductivity of nanocomposite. A differential pulse adsorptive stripping voltammetric method was developed by using the above electrode for highly sensitive determination of chlorpyrifos under optimum instrumental and working conditions. A calibration plot of chlorpyrifos was studied over concentration range, 0.01–100nM and detection limits of 4×10−12M were achieved. The method was successfully applied to well waters and soil samples and recovery values were in good agreement with HPLC–UV method.

Comprehensive analysis of the rotational spectrum of 2,2-dichloropropane

2,2-Dichloropropane, (CH3)2CCl2, is a globular, plastic crystal molecule characterised by an apparently featureless b-type rotational spectrum. The spectrum is complicated by relatively intense isotopic species, nuclear quadrupole hyperfine splitting from two chlorine nuclei, and clustering of the seven lowest normal modes of (CH3)2C35Cl2 in the wavenumber range 250–390cm-1. A comprehensive investigation of this spectrum was carried out on the basis of the room-temperature spectrum recorded up to 338GHz and of the supersonic expansion spectrum at cm-wave frequencies. The ground states of the (CH3)2C37Cl2 and 13CH312CH3C35Cl2 species were assigned for the first time and allowed redetermination of the molecular geometry. The double nucleus hyperfine structure was measured and analysed for both 35Cl2 and 35Cl37Cl species of 2,2-dichloropropane, and differences between orientations of the CCl bond axis and the hyperfine z-axis were determined and discussed. Rotational transitions in first excited states of all seven normal modes were found to be strongly perturbed requiring Coriolis type coupled fits for the (ν9,ν14) and (ν13,ν27) dyads, and the (ν26,ν8,ν21) triad. The precise vibrational energy differences lead to new values for the lowest normal mode frequencies.

Catalytic total oxidation of 1,2-dichloroethane over highly dispersed vanadia supported on CeO2 nanobelts

CeO2 nanobelts were synthesized via a facile aqueous-phase precipitation route under mild conditions (template-free and non-hydrothermal), and then the highly dispersed vanadia catalysts with a wide range of VOx loadings were prepared by a conventional incipient-wetness impregnation method. The target VOx/CeO2 catalysts were characterized in detail and used in catalytic combustion of 1,2-dichloroethane (DCE). The results revealed that the monolayer dispersed VOx (6.0%VOx/CeO2) exhibited the most outstanding initial and stable activities, however, the main product containing carbon was CO, not desired CO2. A reaction mechanism of DCE total oxidation was proposed based on the study of TPSR and in situ FTIR. The first step of this mechanism was considered to be a dissociative adsorption of CCl bonds on Lewis acid sites (such as Ce4+/3+, V5+/4+ or Ce3+–O2−–V5+) via Cl abstraction, and then the dissociated DCE can be oxidized directly to CO2 by surface active oxygen species over pure CeO2. Whereas, over VOx/CeO2 catalysts, the formation of intermediate acetaldehyde was a key step via CH bond activation and hydrogen transfer on VOx species, subsequently, partially oxidized to CO by the lattice oxygen of VOx.

Functionalisation of graphene by edge-halogenation and radical addition using polycyclic aromatic hydrocarbon models: edge electron density-binding energy relationship

Structures and properties of functionalised graphene were investigated using several derivatives of some small polycyclic aromatic hydrocarbons (PAHs) taken as finite size models employing unrestricted density functional theory. The functionalisation reactions included fluorination or chlorination of all the edge carbon sites, addition of H, F or Cl atom, OH or OOH group at the different sites and addition of OH or OOH group at the different sites of the edge-halogenated PAHs. σ-inductive effects of fluorine and chlorine in the edge-fluorinated and edge-chlorinated PAHs, respectively, were found to affect electron density and molecular electrostatic potential (MEP) distributions significantly. σ-holes were located at the MEP surfaces along the CH and CCl bonds of the unmodified and edge-chlorinated PAHs, respectively. The H and F atoms and the OH group were found to add to all the carbon sites of PAHs exothermically, while addition of the Cl atom and the OOH group was found to be exothermic at a few carbon sites and endothermic at the other carbon sites. Enhanced electron densities at the edge carbon sites of the PAHs and binding energies of adducts of H and F atoms and the OH group at these sites were found to be linearly correlated.

Accurate equilibrium structures of fluoro- and chloroderivatives of methane

This work is a systematic study of molecular structure of fluoro-, chloro-, and fluorochloromethanes. For the first time, the accurate ab initio structure is computed for 10 molecules (CF4, CClF3, CCl2F2, CCl3F, CHClF2, CHCl2F, CH2F2, CH2ClF, CH2Cl2, and CCl4) at the coupled cluster level of electronic structure theory including single and double excitations augmented by a perturbational estimate of the effects of connected triple excitations [CCSD(T)] with all electrons being correlated and Gaussian basis sets of at least quadruple-ζ quality. Furthermore, when possible, namely for the molecules CH2F2, CH2Cl2, CH2ClF, CHClF2, and CCl2F2, accurate semi-experimental equilibrium (rSEe) structure has also been determined. This is achieved through a least-squares structural refinement procedure based on the equilibrium rotational constants of all available isotopomers, determined by correcting the experimental ground-state rotational constants with computed ab initio vibration–rotation interaction constants and electronic g-factors. The computed and semi-experimental equilibrium structures are in excellent agreement with each other, but the rSEe structure is generally more accurate, in particular for the CF and CCl bond lengths. The carbon–halogen bond length is discussed within the framework of the ligand close-packing model as a function of the atomic charges. For this purpose, the accurate equilibrium structures of some other molecules with alternative ligands, such as CH3Li, CF3CCH, and CF3CN, are also computed.

PdCl2/Bu4NI: An efficient and ligand-free catalyst for the alkoxycarbonylation of organic chlorides

An active, efficient and ligand-free Pd catalyst system was developed for the alkoxycarbonylation of organic chlorides using PdCl2/Bu4NI catalyst. The influences of various parameters such as solvent, base, ligand and promoter on activity in the alkoxycarbonylation of CH2Cl2 were investigated. Ligand-free PdCl2 with the aid of Bu4NI showed efficient catalytic performance for this inactive transformation, and 87.6% conversion with 67.3% total yield of esters was obtained using 2.5mol% PdCl2 at 110°C. Under optimal conditions, chloroacetates, chloracetone, benzyl chloride and even some aryl chlorides can be carbonylated to corresponding esters in moderate to excellent yields. Moreover, the effect of Bu4NI on the reaction was discussed in detail and it was critical in both stabilizing the Pd catalytic system and activating the inert CCl bond in the reaction.

Carbon and chlorine isotope fractionation during Fenton-like degradation of trichloroethene

Dual isotope approach has been proposed as a viable tool for characterizing and assessing in situ contaminant transformation, however, little data is currently available on its applicability to chlorinated ethenes. This study determined carbon and chlorine isotope fractionation during Fenton-like degradation of trichloroethene (TCE). Carbon and chlorine isotope enrichment factors were εC=−2.9±0.3‰ and εCl=−0.9±0.1‰, respectively. An observed small secondary chlorine isotope effect (AKIECl=1.001) was consistent with an initial transformation by adding hydroxyl radicals (OH) to CC bonds without cleavage of CCl bonds. The relative change in carbon and chlorine isotope ratios (Δ=Δδ13C/Δδ37Cl) was calculated to be 3.1±0.2, approximately equal to the ratio of chlorine and carbon isotope enrichment factors (εC/εCl=3.2). The similarity of the Δ (or εC/εCl) values between Fenton-like degradation and microbial reductive dechlorination of TCE was observed, indicating that application of solely dual isotope approach may be limited in distinguishing the two transformation pathways.

Growth, spectral, thermal and dielectric studies on a new semiorganic NLO material: Di-N-methylanilinium tetrachlorocadmiate(II)

A new semiorganic nonlinear optical material, di-N-methylanilinium tetrachlorocadmiate(II) was grown by slow evaporation solution method at ambient temperature. The absorption of the compound was studied by UV–vis absorption spectral analysis. The suitability of the optical property was ascertained through optical transmittance study. The sharp and well defined Bragg peaks in the powder X-ray diffraction pattern confirm its crystallinity. Thermal stability and decomposition pattern of the compound were studied by using TG-DTG and DTA analyses. The different kinds of protons and carbons were assigned through nuclear magnetic resonance (NMR (13C and 1H)) spectroscopic techniques. The Fourier infrared spectrum (FTIR) characterizes the vibration frequencies due to NC, CCl, CdCl42− and other chemical bond vibrations. The second harmonic generation (SHG) efficiency of the compound was measured by suing Kurtz–Perry powder techniques and it shows that the compound has SHG efficiency one and a half times greater than of potassium dihydrogen phosphate (KDP). The dielectric constant and dielectric loss of the compound decrease with increases in frequencies.

Cu(0)/2,6-bis (imino)pyridines catalyzed single-electron transfer-living radical polymerization of methyl methacrylate initiated with poly(vinylidene fluoride-co -chlorotrifluoroethylene)

A series of 2,6-bis(imino)pyridines, as common ligands for late transition metal catalyst in ethylene coordination polymerization, were successfully employed in single-electron transfer-living radical polymerization (SET-LRP) of methyl methacrylate (MMA) by using poly(vinylidene fluoride-co-chlorotrifluoroethylene) (P(VDF-co-CTFE)) as macroinitiator with low concentration of copper catalyst under relative mild-reaction conditions. Well-controlled polymerization features were observed under varied reaction conditions including reaction temperature, catalyst concentration, as well as monomer amount in feed. The typical side reactions including the chain-transfer reaction and dehydrochlorination reaction happened on P(VDF-co-CTFE) in atom-transfer radical polymerization process were avoided in current system. The relationship between the catalytic activity and the chemical structure of 2,6-bis(imino)pyridine ligands was investigated by comparing both the electrochemical properties of Cu(II)/2,6-bis(imino)pyridine and the kinetic results of SET-LRP of MMA catalyzed with different ligands. The substitute groups onto N-binding sites with proper steric bulk and electron donating are desirable for both high-propagation reaction rate and CCl bonds activation capability on P(VDF-co-CTFE). The catalytic activity of Cu(0)/2,6-bis(imino)pyridines is comparable with Cu(0)/2,2′-bipyridine under the consistent reaction conditions. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4378–4388

Mechanism and kinetics of the synthesis of phenyltrichlorosilane from trichlorosilane and chlorobenzene by gas phase condensation

The mechanism of the synthesis of phenyltrichlorosilane from trichlorosilane and chlorobenzene by gas phase condensation was studied. A kinetic model with 28 species and 56 elementary reactions was established, which was validated by experimental results from a tubular reactor under wide reaction conditions. The mole fraction profiles of the reactants and products from the kinetic model were in good agreement with the experimental results. This gas phase condensation reaction mainly followed an insertion mechanism of dichlorosilylene into the CCl bond to form C6H5SiCl3. A reaction flux analysis showed that 99% of C6H5SiCl3 was generated from the insertion reaction, 74% of SiCl3H was decomposed into SiCl2 and 91% of SiCl2 was inserted into C6H5Cl to form C6H5SiCl3. The proposed mechanism and kinetic model are useful for developing and designing commercial reactors to produce phenyltrichlorosilane.

Mg–Cu bimetal system for selective C[sbnd]F bond activation

Bimetal system of Mg–CuCl in DMI for selective CF and CCl bonds activation has been examined. This article involves (1) a short overview of bimetal system of Mg-metals for selective CF bond activation, (2) CF bond activation of alkyl trifluoroacetates leading to alkyl difluoro(trimethylsilyl)acetates via difluoroketene silyl acetal, (3) selective CCl bond activation of 3- and 4-chloropentafluoroethylbenzenes, (4) CF bond activation of substituted benzotrifluorides and (5) microscopic observation of an active site of magnesium surface formed in Mg–CuCl system and elucidation of reaction mechanism of CCl and CF bond activation at the active site.

Experimental investigation and modeling of the kinetics of CCl4 pyrolysis behind reflected shock waves using high-repetition-rate time-of-flight mass spectrometry

The pyrolysis kinetics of CCl(4) behind reflected shock waves was studied with high-repetition-rate time-of-flight mass spectrometry. For modeling, quantum mechanical calculations were performed to evaluate the dissociation energies of CCl bonds for the different CCl(x) (x = 1 to 4) radicals. Good agreement with the JANAF thermochemical table was found. With the reaction mechanism developed for CCl(4) decomposition satisfactory agreement with experimental results was obtained. The investigations show the importance of C(2)Cl(2) formation for understanding the processes of carbon cluster growth leading to carbonaceous particle formation.

Preparation of gold nanoparticles by surfactant-promoted reductive reaction without extra reducing agent

Cetyltrimethyl ammonium bromide (CTAB) has been extensively applied in the solution-phase synthesis of many types of colloidal nanoparticles. However, the uses of CTAB were mainly considered as template or capping agents to form controllable shape and protect the product from agglomeration. Here it was discovered that CATB could serve as a very mild reductant to reduce gold salt precursors preparing gold nanoparticles (GNPs) at base environment. CTAB acted as the reducing agent suffering a partial degradation and forming CTA macro radicals. FTIR proved the formation of CCl and/or CBr bond after CTAB degraded. The characterization of synthesized GNPs was examined by UV–Vis spectra, TEM and XRD. Several factors affecting the process of reaction, such as the amount of NaOH, the molar ratio of CTAB and HAuCl4, the reaction temperature, the effect of light and oxygen, and stirring were discussed.

Catalytic combustion of chlorobenzene over Ru-doped ceria catalysts: Mechanism study

To investigate the mechanism of the catalytic combustion of chlorobenzene over pure CeO2 and Ru doped CeO2 catalysts, we examined the oxidation reaction in depth by temperature-programmed surface reaction (TPSR) technique and a series of supplementary experiments. The results suggest that the CCl bond in chlorobenzene molecule can be dissociated easily on Ce3+/Ce4+ active sites, and the dissociated chlorobenzene can be rapidly oxidized into CO2 and H2O by surface reactive oxygen or lattice oxygen. The chlorine species dissociatively adsorbed on the active sites can result in the rapid deactivation of catalysts and be removed in form of Cl2 via the Deacon Reaction catalyzed by RuO2 or CeO2, which would improve the catalyst stability. Additionally, the partial chlorination of RuO2 or CeO2 possibly occurs during the long reaction, which is responsible for the production of dichlorobenzene by-products.

Cross coupling reactions of multiple C[sbnd]Cl bonds of polychlorinated solvents with Grignard reagent using a pincer nickel complex

The nickel(II) complex of a bulky pincer-type ligand, N,N′-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamido, was examined for sp3–sp3 coupling of Grignard reagents with polychlorinated solvents. The nickel(II) complex catalyzed CC coupling of polychlorinated alkyl halides, such as dichloromethane (CH2Cl2), chloroform (CHCl3), and carbon tetrachloride (CCl4), with various Grignard reagents. The effective activation of multiple CCl bonds proceeded under ambient reaction conditions and within a short time (20min). This catalyst displays the highest activity yet reported for this reaction type, with catalyst loading as low as 0.4mol% and turnover frequency (TOF) as high as 724h−1. The catalyst is capable of replacing all chlorine atoms with CC bond formations for all of the polychlorinated solvents under investigation. The catalytic process could prove to be an efficient method of remediation of toxic polychlorinated solvents while generating synthetically and commercially important chemicals.

Carbon 1s photoelectron spectroscopy of the chlorinated methanes: Lifetimes and accurate vibrational lineshape models

Construction of accurate lineshape models for chlorosubstituted hydrocarbons is challenging. In this account the problem has been investigated thoroughly for the chloromethane series, CH4−nCln, n=1–4, using high-resolution experimental data and extensive theoretical calculations. The CCl bond contraction following ionization is a key parameter for a quantitative description of the vibrational excitation for all four molecules. We determine this quantity accurately for the title molecules and also propose approximate approaches that may applied to larger molecules. Having developed accurate vibrational lineshape models as well as reliable estimates of the instrumental broadening in each case, the carbon 1s hole lifetime broadening is determined from a fit to the experimental spectrum for each molecule. The resulting values for the lifetime broadening are 88±5meV for CH3Cl, 80±5meV for CH2Cl2, 74±5meV for CHCl3 and 62±5meV for CCl4. The lifetime widths decrease systematically with the number of chlorine substituents and correlate excellently with the valence occupancy of the core-ionized carbon. This indicates that the one-center model for Auger decay of the core hole is valid for the present series of molecules.

Dynamics of C[sbnd]Cl bond fission in photodissociation of 2-furoyl chloride at 235 nm

The photodissociation dynamics of 2-furoyl chloride at 235nm has been investigated, employing resonance-enhanced multiphoton ionization technique and time-of-flight mass spectrometry. Both the Cl fragments, Cl(2PJ=3/2, relative quantum yield 0.85±0.11) and Cl∗(2PJ=1/2), have the recoil anisotropy parameter (β) value close to zero, and show bimodal translational energy distributions. The branching ratio of the high kinetic energy CCl bond scission to the low energy CCl scission is 0.78/0.22. The dominant high kinetic energy channel arises mainly because of electronic pre-dissociation. But, the low energy channel results from the ground electronic state of 2-furoyl chloride, formed subsequent to non-radiative relaxation of the initially prepared excited state.

Pd-catalyzed hydrodehalogenation of chlorinated olefins: Theoretical insights to the reaction mechanism

Density functional theory calculations are applied to study energetics of trichloroethene (TCE) hydrodechlorination over pure Pd(111), chlorine-covered Pd(111), and Pd island supported by Au(111). Our results show that in all cases CCl bond breakings take place more readily than CH bond formations and that TCE dechlorinates fully producing CCH precursors for the hydrogenations. The reaction pathway through radical-like species provides a possible explanation to the experimental product distributions that show a nominal amount of lesser chlorinated species in the presence of excess hydrogen. The surface chlorine resulted from the TCE decomposition weakens the binding of the adsorbates and reduces the gap between the dechlorination and hydrogenation barriers but is not expected to affect the overall reaction route. The underlying gold induces stronger adsorption and decreases the activation barriers considerably compared to the pure Pd(111). The change in Gibbs free energy between the gas-phase molecule and the activated surface species explains the experimentally observed reactivity ordering among chlorinated ethenes. Although vinyl chlorine has a stronger CCl bond than TCE, it dechlorinates faster when introduced from the gas phase to the catalyst surface.

Novel microwave synthesis of ruthenium nanoparticles supported on carbon nanotubes active in the selective hydrogenation of p-chloronitrobenzene to p-chloroaniline

Carbon nanotubes (CNTs) have been employed for the preparation of supported ruthenium nanoparticles using, for the first time, a low boiling alcohol or a mixture ethanol/water as solvent/reducing agent under microwave irradiation as heating source. These systems were employed as catalysts in the selective hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) and resulted efficient systems for the selective reduction of the nitro group in p-CNB under mild reaction conditions (60°C and 4MPa of H2), while the CCl bond remains intact, thus allowing the almost complete substrate conversion with total selectivity to the target product. These supported ruthenium nanoparticles are characterized by small average diameters and narrow particle size distributions, even if synthesized in the absence of any additional stabilizing agents and appear very promising systems also for other catalytic applications.