Catalytic dechlorination of aromatic chloride with supported palladium catalysts in alkaline 2-propanol: influence of hydrocarbon solvents

Summary Catalytic dechlorination of p-chloroanisole (p-chloromethoxybenzene) was carried out in a solution of NaOH in 2-propanol in the presence of Pd/Al₂O₃ or Pd/C at 40°C. When aromatic hydrocarbons such as toluene or benzene were added to the solution, the dechlorination rates were strongly suppressed. However, aliphatic hydrocarbons such as n-hexane or cyclohexane hardly affected the dechlorination rates.     

Enhancement of the catalytic hydrodechlorination of tetrachloroethylene in methanol at mild conditions by water addition

The dechlorination of tetrachloroethylene (PCE) over carbon-supported palladium catalyst (Pd/C) in methanol (MeOH) at mild conditions was enhanced through the addition of water to the reaction mixture. The dechlorination of PCE was accelerated by increasing the amount of water in the mixture from 0% to 50%, and beyond which the reaction slowed down, however. The presence of water in the mixture enhanced the adsorption of PCE onto the Pd/C but compromised the solubility of H₂ gas in the mixture. It was also noted that the selectivity of the HDC reaction was improved with the increase in the amount of water in the mixture as the formation of trichloroethylene (TCE) was completely eliminated when the HDC was carried out in mixtures with 50% water or more. Other chlorinated intermediates were not detected in all the reactions.     

Dechlorination of polychlorinated biphenyls in electron impact mass spectrometry: Regioselective analysis using 35Ci-labelled compounds

Four tetrachlorinated bipbenyls were chlorinated with ³⁵Cl₂ to yield seventeen polychlorinated biphenyls (PCBs) substituted once or twice with chlorine enriched in ₃₅Cl. Gas chromatographic analysis of the mixtures allowed the identification of the labelled PCBs produced by comparison of their relative retention times with published values. This also permitted the assignment of the position of the labels in these molecules. Mass spectrometric determination of the ³⁵Cl/³⁵Cl ratio of the ions corresponding to successive dechlorination of these PCBs in positive-ion electron impact (EI) allowed quantification of the residual ³⁵Cl label in these ions. Chlorines in the ortho position are lost preferentially to those in meta or para positions. The first dechlorination reaction was found to be totally regioselective for at least two PCB congeners.     

Degradation of Carbon Tetrachloride by nanoscale Zero‐Valent Iron @ magnetic Fe3O4: Impact of reaction condition,Kinetics, Thermodynamics and Mechanism

Nano‐scale zero‐valent Iron (nZVI) attached on the Fe₃O₄ nanoparticles were prepared and creatively applied in the reductive dechlorination of Carbon Tetrachloride (CT). The characterization results of the synthesized composite indicated a main component of nZVI particles assembled on the surface of Fe₃O₄ with a layer of iron‐oxide film on the periphery, of which the dispersibility was better and the specific surface area was larger. The effects of different reaction conditions like temperature, initial pH values, Fe⁰@Fe₃O₄ dosage and initial CT concentrations on the removal of CT were evaluated. Under the optimum conditions, the Fe⁰@Fe₃O₄ composites showed a CT removal efficiency of 89.1% in 60 min, which was much greater than that of nZVI (61.7%) and Fe₃O₄ particles (14.3%). The removal process obeyed the pseudo‐first‐order kinetic model. Synergy effects of the constituents in the composite which can promote the relative rates of mass transfer to reactive sites were proposed to be existed and the magnetism of Fe₃O₄ could help to overcome the aggregation and surface passivation problem of nZVI. Thus, Fe⁰@Fe₃O₄ nanoparticles in our study can effectively complete the reductive dechlorination of CT and an improved nZVI catalyst is provided for the remediation of chlorinated organic compounds.     

Halocarbons in Aqueous matrices from the Rennick Glacier and the Ross Sea (Antarctica)

Aqueous matrices from Antarctica were analysed for three volatile chlorinated hydrocarbons (VCHCs): tetrachloromethane (CCl₄), trichloroethylene (C₂HCl₃) and tetrachloroethylene (C₂Cl₄). The matrices analysed were snow from Rennick Nèvè and Rennick Glacier sampled during the Italian Expeditions of 1995/96 and 1996/97, respectively, and seawater, pack ice, sea-microlayer, subsuperficial water and freshwater, collected during the Italian Expedition of 1997/98. Extractions from the aqueous matrices were carried out in Antarctica (the laboratories of the Italian Base, Terra Nova Bay). Because of the critical space–time conditions in these laboratories, an extraction procedure was developed, suitable for large volumes of water (10?L), in order to combine the extraction of other classes of organic compounds (polychlorinated biphenyls, polycyclic aromatic hydrocarbons and chlorinated pesticides) with those of our direct interest. The VCHC organic extracts were analysed in Italy by GC-ECD and GC-MS. The analyses confirmed the presence of the three halocarbons in Antarctica in quantities ranging from units to some dozens of nanograms per kilogram. The results were evaluated with respect to the local distribution of these compounds and their diffusion on a global scale.     

Effects of exogenic chloride on oxidative degradation of chlorinated azo dye by UV-activated peroxodisulfate

Recently, the degradation of organic compounds in saline dye wastewater by sulfate radicals (SO₄⁻)-based advanced oxidation processes (AOPs) have attracted much attention. However, previous studies on these systems have selected non-chlorinated dyes as model compounds, and little is known about the transformation of chlorinated dyes in such systems. In this study, acid yellow 17 (AY-17) was selected as a model of chlorinated contaminants, and the degradation kinetics and evolution of oxidation byproducts were investigated in the UV/PDS system. AY-17 can be efficiently degraded (over 98% decolorization) under 90 min irradiation at pH 2.0–3.0, and the reaction follows pseudo-first order kinetics. Cl^‒ accelerated the degradation of AY-17, but simultaneously led to an undesirable increase of absorbable organic halogen (AOX). Several chlorinated byproducts were identified by liquid chromatography-mass spectrometry (LC–MS/MS) in the UV/PDS system. It indicates that endogenic chlorine and exogenic Cl^– reacted with SO₄⁻ to form chloride radicals, which are involved in the dechlorination and rechlorination of AY-17 and intermediates. The possible degradation mechanisms of AY-17 photooxidative degradation are proposed. This work provides valuable information for further studies on the role of exogenic chloride in the degradation of chlorinated azo dyes and the kinetic parameters in the PDS-based oxidation process.     

Electron beam treatment of chloroethylenes/air mixture in a flow reactor

Decomposition of chloroethylenes under electron beam irradiation in a flow reactor has been studied with different reaction environments, various initial concentrations and in the presence and absence of vaporized water. Three chlorinated ethylenes—dichloroethylene (DCE), trichloroethylene (TCE), perchloroethylene (PCE)—were used as model chlorocarbons. The degree of decomposition was 48% for DCE, 98% for TCE and 90% for PCE in air reaction environment at an initial concentration of 2000 ppm and a dose of 18–20 kGy irradiation. In the presence of water vapor (5600 ppm) decomposition of TCE was about 10% higher than in dry air. The main products were found to be CO, CO₂, HCl, dichloroacetic acid (DCAA), dichloroacetyl chloride (DCAC) and dichloroethyl ester acetic acid (DEAA). DCAA, DCAC and DEAA were identified as chloro-oxygenated hydrocarbons, which could be decomposed with CO and CO₂ production. Concentration profiles show that intermediate products and yields of CO and CO₂ decrease with decreasing number of chlorine substitutions in the initial hydrocarbons.     

Dechlorination and oxidation for waste poly(vinylidene chloride) by hydrothermal catalytic oxidation on Pd/AC catalyst

Hydrothermal catalytic oxidation was an effective method in the dechlorination and oxidation of waste poly(vinylidene chloride) (PVC) on Pd/AC catalyst. The PVC was decomposed by hydrothermal catalytic oxidation in the system of NaOH at appropriate temperature in our experiments. The degree of dechlorination and oxidation increased with increasing concentration of H₂O₂, reaching up to 90% and 50% under the condition of 180 °C and 0.5 MPa pressure. The main products were Cl⁻ and CO₂, and the rest comprises a range of water-soluble organic acids, which were nontoxic and can be treated by biological purification. Therefore, the hydrothermal catalytic oxidation had significant potential in application for treatment of chlorinated waste plastics.     

Application of nano-scale zero-valent iron adsorbed on magnetite nanoparticles for removal of carbon tetrachloride: Products and degradation pathway

Nano-scale zero-valent iron (nZVI) attached to Fe₃O₄ nanoparticles (Fe⁰@Fe₃O₄), which has better dispersibility and a larger specific surface area than the nanoparticles alone, were prepared and applied to the reductive dechlorination of carbon tetrachloride (CT). CT removal efficiencies by Fe⁰@Fe₃O₄ composites with different ratios of the two components were compared. Under optimum conditions, when the Fe⁰/Fe₃O₄ ratio was 1:2, almost no CT was detected after 50 min and it took only about 30 min to reach a removal efficiency of 90%, compared with 120 min for an Fe⁰/Fe₃O₄ ratio of 1:4. An increase in the amount of nZVI in the catalyst effectively improved the removal of CT and accelerated the reaction rate. Chloroform was the main product. Compared with Fe₃O₄ alone, a significant increase in the solution concentrations of ferrous and ferric ions occurred in the Fe⁰@Fe₃O₄ system: both Fe²⁺ and Fe³⁺ reached their maximum concentrations at 60 min and then tended to decline over the next 60 min. The increase in Fe²⁺ concentration was attributed to the reaction between nZVI and CT, which produces ferrous ions when electrons transfer from Fe⁰ to organic chlorides. Synergistic effects between the composite constituents promoted the relative rates of mass transfer to reactive sites and Fe²⁺ generated in solution facilitated the reduction of chlorinated organic pollutants by magnetite. Thus, Fe⁰@Fe₃O₄ nanoparticles effectively achieved reductive dechlorination of CT and provide an improved nZVI catalyst for the remediation of chlorinated organic compounds.     

Catalytic dechlorination of Aroclor 1242 by Ni/Fe bimetallic nanoparticles

Ni/Fe bimetallic nanoparticles were synthesized for treatment of Aroclor 1242, in order to evaluate their applicability for in situ remediation of groundwater and soil contaminated by polychlorinated biphenyls (PCBs). Our experimental results indicate that the total PCB concentration changed during the reduction of 3,5-dichlorobiphenyl (PCB 14), and biphenyl was produced as the final product. Initially, the concentration of 3-chlorobiphenyl (PCB 2) was increased in the prophase reaction and then slowly decreased, suggesting that Aroclor 1242 was first adsorbed by Ni/Fe nanoparticles, and then, the higher chlorinated congeners were converted gradually to the lower chlorinated congeners, and finally to biphenyl. The dechlorination efficiency of Aroclor 1242 reached approximately 80% at 25°C in just 5h, then 95.6% and 95.8% in 10h and 24h, respectively. The study revealed that high Ni/Fe nanoparticle dosage and high Ni content in Ni/Fe nanoparticles favor the catalytic dechlorination reaction. Moreover, a comparison of different types of catalysts on the dechlorination of Aroclor 1242 indicated that Ni/Mg and Mg powders showed a greater reactivity than Ni/Fe and Fe nanoparticles, respectively.     

Synthesis of New N‐alkyl‐5‐formyl‐2‐methylpyrrole Derivatives from Glucosamine

Glucosamine hydrochloride 1 was treated with 1,3‐dicarbonyl compounds to obtain 2‐methyl‐5‐(1,2,3,4‐tetrahydroxy‐butyl) pyrrole 2a and 2b , respectively. Under the role of NaIO₄, 2a and 2b were successfully transformed into the related 5‐formal pyrrole derivative 3a and 3b , respectively. Compounds 4a – 4d and 5a – 5e were obtained by reacting 3a and 3b with chlorinated hydrocarbons by alkylation reactions, respectively. The structures of all new products were confirmed by IR, NMR, and HRMS spectra.     

土壤有机氯脱氯转化的界面交互反应*

有机氯杀虫剂、除草剂等难降解有机物是重要的土壤污染物。近年来,有机氯脱氯转化的界面过程已成为土壤环境科学的研究热点。本文综述了土壤有机氯脱氯转化的界面非生物过程、界面生物过程以及界面生物－非生物交互反应过程。界面脱氯转化过程与主要土壤化学过程、土壤根际过程相互关联,该过程中,铁物种循环与铁氧化物的异化还原溶解扮演了重要角色。     

Gaschromatographische Untersuchung der Adsorptionseigenschaften von Silicalit und ZSM-5

High silica molecular sieves (silicalite, ZSM-5) were tested as adsorbents for gas chromatographic trace analysis. Therefore the retention behaviour of low-boiling organic compounds (hydrocarbons, halogenated hydrocarbons, amines, alcohols and ethers) on these materials was investigated. The specific retention volumes at different temperatures have been determined and elution orders and peak shapes were studied. The retention data allow a simple calculation of the breakthrough volumes (dynamic adsorption capacity) and the chromatographic characterisation of the adsorbents. Both nitrogen and oxygen containing compounds could not—or at least unreproducibely—be eluated up to 300°. The elution order and the peak shape of compounds with the same number of carbon atoms but different geometric and electronic structure (e.g.n-butenes;n-hexane, cyclohexane, benzene) can be explained by the action of exclusion effects and different diffusion barriers. On the basis of calculated breakthrough volumes we conclude that silicalite should be useful in the preconcentration of both saturated C₃–C₆ hydrocarbons and C₁–C₂ chlorinated hydrocarbons from gaseous streams.     

Dechlorination of poly(vinylidene chloride) in NaOH/ethylene glycol as a function of NaOH concentration, temperature, and solvent

The wet dechlorination treatment of poly(vinylidene chloride) (PVDC) was evaluated at atmospheric pressure in a solution of NaOH in ethylene glycol (EG), as a function of NaOH concentration, temperature, and solvent. Hydroxide ion from NaOH was required for dechlorination with EG acting solely as a solvent. The wet treatment exhibited significantly enhanced dechlorination efficiency over traditional thermal techniques, with a reaction efficiency as high as 92.8% in 1.0 M NaOH at 190 °C. Dechlorination reactions of PVDC in both NaOH/EG and NaOH/H₂O were expressed by an apparent first-order reaction. At 190 °C, the apparent rate constant in 1.0 M NaOH/EG was approximately 1.4 times larger than in 1.0 M NaOH/H₂O, with an apparent activation energy of 82.8 kJ mol⁻¹, indicating that the reaction proceeded under chemical control. The degree of dechlorination increased with increasing reaction temperature, favouring the elimination of HCl over the hydroxyl substitution of chloride.     

Dechlorination of poly(vinyl chloride) using NaOH in ethylene glycol under atmospheric pressure

A solution of NaOH dissolved in ethylene glycol (EG) was effective in the dechlorination of poly(vinyl chloride) (PVC) at atmospheric pressure. The degree of dechlorination increased with increasing temperature, reaching a maximum of 97.8% at 190 °C. The dechlorination proceeded under chemical control and exhibited first-order kinetics with an apparent activation energy of 170 kJ mol⁻¹. The apparent rate constant for dechlorination in 1.0 M NaOH/EG was approximately 150 times greater than that in 1.0 M NaOH/H₂O. In addition, dechlorination was faster at atmospheric pressure in NaOH/EG than under high pressure in NaOH/H₂O. The dechlorination reaction occurs via a combination of E2 and S_N2 mechanisms.     

Effect of NaOH on the solubility of fluorocarbon in alcohol–NaOH systems

We propose a dechlorination process that allows safe and environmental conversion of chlorinated fluorocarbons. Starting with dissolving a fluorocarbon in an alcohol–NaOH solution, the fluorocarbons are reacted with alcohol–NaOH solvents at room temperature and pressure. In this work, the effect of the NaOH concentration on the solubility of CCl₂F₂ (CFC-12), CH₂F₂ (HFC-32), C₂HF₅ (HFC-125), C₂H₂F₄ (HFC-134a) and C₂H₄F₂ (HFC-152a) in methanol–NaOH, ethanol–NaOH and 1-propanol–NaOH solutions was measured. The experimental salting-out effects can be explained by solvation of a few alcohol molecules on sodium ion. Setchenov coefficients were determined and found to be independent of temperature.     

Kinetic study of liquid-phase hydrodechlorination of hexachlorobenzene on Ni/C and 2%PdNi/C

Liquid-phase hydrodechlorination of hexachlorobenzene was kinetically studied in the presence of both nickel (Ni/C) and palladium-promoted nickel (2%PdNi/C) catalysts under different reaction conditions. Molecular hydrogen (at 1 and 20 atm) and sodium borohydride (NaBH₄) were used as reducing agents. In the presence of the nickel catalyst, the hydrodechlorination of C₆Cl₆ occurs via a consecutive mechanism (removal of one chlorine atom from the substrate at each stage), whereas with the 2%PdNi/C catalyst, the transformation of C₆Cl₆ occurs via both consecutive and multiplet mechanism (with the elimination of several chlorine atoms without desorption of the chloroaromatic substrate from the catalyst surface). The promotion of the nickel catalysts with palladium substantially changes the selectivity of formation of intermediate products of C₆C1₆ dechlorination. The mechanism of hydrodechlorination of hexachlorobenzene was suggested that explained the presence of only certain products of partial dechlorination of hexachlorobenzene in the reaction medium.     

The determination of the gases released during heating of a flame retardant for polymers

The oxidative degradation of HET-acid (1,4,5,6,7,7-hexachlorobicyclo [2.2.1] hept-5-en-2, 3-dicarboxylic acid) is studied by the combination of TG, FTIR, MS and GC-MS. The gases evolved during the decomposition of this flame retardant are investigated on-line by FTIR and by MS. Simultaneously the evolved gases are collected by an adsorbent and, after the thermal experiment, desorbed to release the volatile products for identification using GC-MS. The combination of these techniques offers the unambiguous identification of the evolved products as a function of temperature. The main identified products are CO₂, H₂O, Cl₂, HCl, C₂Cl₄, maleic acid anhydride, HET-acid anhydride, chlorinated cyclic hydrocarbons and chlorinated unsaturated linear hydrocarbons.     

A Study of picosecond dehalogenation of chlorobenzene anions in liquids by positronium inhibition measurements

Radiation chemistry and results of Ps yields indicate that the following processes occur in the positron spur in solution of halogen-substituted hydrocarbons, RX_n: e⁺ + e^? → Ps, e^? + RX _n → (RX_n)^? → RX_n?1 + X^?, e⁺ + (RX_n)^? → Ps + RX_n, e⁺ + X^? → [X^?, e⁺]. Hence the trapped electron can form Ps only if (RX _n)^? is stable or has a lifetime that is longer than o comparable to the Ps formation time. Previous studies have shown that some of the strongly chlorinated benzenes (n = 4.5 give reasonable inhibition in benzene but not in linear hydrocarbons. The reason is very probably that the dechlorination time is much shorter in benzene than in saturated hydrocarbons because Cl^? is more strongly solvated in benzene than in non-aromatic hydrocarbons. To test those ideas further we have begun detailed studies of solutions of the possible “intermediate” inhibitors, viz. 1,2,3,5- and 1,2,4,5-C₆H₂Cl₄, in mixtures of C₆H₆/C₆H₁₄ different methyl-substituted benzene aniline, anisole, dioxane and ethylbenzene. The results are discussed and interpreted in terms of the spur model. The Ps inhibition efficiency of the two isomeric forms of tetrachlorobenzene studied, appears most probably to depend on intramolecular electron transfer with subsequent dehalogenation of the molecular anion on a picosecond timescale. The divergence in inhibitor efficiency obtained for the chlorobenzenes when dissolved in aromatic solvents compared to the same solutes when dissolved in a saturated alkane appears most probably to be caused by complex formation between the initially formed chlorobenzene anion and benzene molecules, which permits a rapid relaxation of the molecular anion with subsequent bond stretching and expulsion of the chloride anion.     

Regioselectivity of the oxygen addition-induced dechlorination of PCBS and DDT metabolites in electron capture mass spectrometry

The electron capture mass spectra of 28 ³⁵Cl-labeled polychlorinated biphenyls (PCBs) and 4 ³⁷Cl-labeled 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) metabolites were obtained by using a 20% oxygen in methane mixture as the reagent gas. The degree of regioselectivity of the PCB oxygen addition-induced dechlorination reaction was determined by measurement of the residual amount of label in the M-19 ions produced by addition of O₂ and subsequent loss of OCl from the molecule. Chlorine was lost in a random manner from the PCBs, contrary to the dechlorination reaction observed when methane alone was used. For the DDT metabolites, many dechlorination reactions were observed in addition to the one that generated the M-19 ions. Loss of Cl, loss of Cl₂, and addition of O₂ with the loss of one or two HCl molecules also were seen. These various dechlorination reactions involved only the aliphatic chlorines. Addition of O₂ followed by loss of Cl at the beta position of 2,2-bis(4-³⁷Cl-chlorophenyl)-1-chloroethylene and 2,2-bis(4-³⁷Cl-chlorophenyl)-1,1-dichloroethylene may be due to the ability of the diphenyl methane moiety to stabilize the intermediates. Formation of an ion that corresponds to 4,4′-dichlorobenzophenone also was observed for three of these labeled DDT metabolites.