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.     

Dechlorination of N-chloro poly(hexamethylene adipamide) and N-chloro poly(ε-caprolactam) products to the corresponding polyamides

A rapid dechlorination method of N-chloro poly(hexamethylene adipamide) and N-chloro poly(ε-caprolactam) to the corresponding polyamides was studied. This method can be used for molecular weight determinations of N-chloro polyamides by viscosimetric measurements. The dechlorination was achieved in formic acid solution by the reaction of N-chloro polyamides with trialkyl phosphites. The reaction was exothermic and vigorous and was applied to a series of products of various degrees of N-chlorination covering the range of 0–100%. No N—Cl was detected by iodimetric titration of the dechlorination products. The dechlorination of N-chloro polyamides was demonstrated by infrared (IR) spectroscopy. No significant molecular weight reduction except that taking place in the N-chlorination reaction of poly(hexamethylene adipamide) was observed.     

Dechlorination of polychlorinated biphenyls in electron-capture negative-ion chemical ionization mass spectrometry

The electron-capture negative-ion chemical Ionization mass spectra of 36 ³⁵Cl mono- and di-labelled penta- and hexachlorobiphenyls were studied. Under the conditions of the analyses, the dechlorination of these congeners probably proceeds through electrophilic hydrogen atom attachment followed by rapid loss of the chlorine atom at the same position. These dechlorination reactions occur regioselectively. When present, ortho-chlorines are lost preferentially to meta- and para-chlorines. The extent of the dechlorination reaction, as seen by the relative abundance of the [MH ? Cl]^? ions, decreases with increasing number of ortho-chlorines.     

Catalytic dechlorination of aromatic chlorides with Pd/C catalyst in alkaline 2-propanol: activity enhancement by the addition of methanol

Summary p- and o-Chloroanisole were catalytically dechlorinated with Pd/C at 30°C in a solution of NaOH in mixtures of 2-propanol and methanol. The dechlorination rate of p-chloroanisole in the mixture containing 1% methanol was 12 times as high as that in 2-propanol alone. The dechlorination rate of o-chloroanisole was also enhanced by the addition of a small amount of methanol.     

A graphite oxide-based nickel catalyst for reductive dechlorination of polychlorinated aromatic hydrocarbons

Heterogeneous Ni-containing catalysts based on graphite oxide were prepared and their activity in the dechlorination of polychlorinated aromatic hydrocarbons by different organosilanes was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1023–1025, June, 2000.     

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.     

Dechlorination of 2,4-dichlorophenoxyacetic acid using biochar-supported nano-palladium/iron: Preparation,characterization, and influencing factors

In the present study, peanut shell, a green waste raw material, was used to prepare biochar (BC) and to obtain BC-supported nano-palladium/iron (BC-nPd/Fe) composites for removing 2,4-dichlorophenoxyacetic acid (2,4-D) from water. Characterization analysis demonstrated that nPd/Fe particles were well dispersed on the BC surface with weakened magnetic properties. The average particle diameter and specific surface area of nPd/Fe were 101.3 nm and 6.7 m² g⁻¹, whereas the corresponding values of the BC-nPd/Fe materials were 88.8 nm and 14.8 m² g⁻¹, respectively. Several factors were found to influence the dechlorination of 2,4-D, including the weight ratio of BC to Fe, Pd loading ratio, initial solution pH, 2,4-D concentration, and reaction temperature. Dechlorination results indicated that the 2,4-D removal and phenoxyacetic acid (PA) generation rates were 44.1% and 20.1%, respectively, in the nPd/Fe system, and 100.0% and 92.1%, respectively, in the BC-nPd/Fe system. The dechlorination of 2,4-D was well described by the pseudo-first-order kinetic model (R² > 0.97), and the observed rate constants k_obs were 0.0042 min (nPd/Fe) and 0.0578 min (BC-nPd/Fe), respectively. The reaction mechanism indicated that the dechlorination hydrogenation was the main process to remove 2,4-D from water in the BC-nPd/Fe system. In addition, BC inhibited the formation of a passivation layer on the particle surface during the reaction, thus maintaining the high reactivity of BC-nPd/Fe. The easy preparation technique, high 2,4-D dechlorination capacity, and mild reaction conditions suggest that BC-nPd/Fe may be a promising alternative composite to remove 2,4-D from water.     

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.     

Polyfluorinated enol acetates

The synthesis of polyfluorinated enol acetates has been performed by reductive dechlorination of chloropolyfluoroketones with zinc in Ac₂O. Under these conditions, hexafluoroacetone is preferably reduced at the carbonyl group.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 174–176, January, 1994.     

Electrogenerated Fe(I) Porphyrins: Efficient Electrocatalysts for Reductive Dechlorination of DDT in N,N′‐Dimethylformamide

Two iron(I) porphyrins were electrogenerated and then utilized as catalysts for the reductive dechlorination of 1,1‐bis(4‐chlorophenyl)‐2,2,2‐trichloroethane (DDT) in N,N′‐dimethylformamide. No reaction is observed between DDT and the Fe(III) or Fe(II) forms of the porphyrin, but the electrogenerated Fe(I) porphyrin efficiently catalyzes the electroreduction of DDT to give (1,1‐bis(4‐chlorophenyl)‐2,2‐dichloroethane) DDD, (1,1‐bis(4‐chlorophenyl)‐2,2‐dichloroethylene) DDE and (1,1‐bis(4‐chlorophenyl)‐2‐dichloroethane) DDMU as determined by GC‐MS analysis. The reductive dechlorination was monitored by electrochemistry, controlled potential electrolysis and spectroelectrochemistry and a mechanism for the reaction involving the reduced porphyrins and DDT is proposed. Comparisons are also made between the catalytic properties of metalloporphyrins containing iron, cobalt and manganese central metal ions under the same solution conditions.     

氯气脱除技术研究进展

氯气(Cl₂)是一种对人体健康和大气环境有严重威胁的高毒性污染物,广泛存在氯碱工业的生产过程中,是含氯尾气的主要成分。含氯尾气的高效清洁脱除已成为研究重点与难点。吸附法和吸收法脱氯技术是目前主要的研究方向。本文以Cl₂的高效率脱除为目标、经济性脱除为理念、绿色化脱除为方向,综述了吸附法和吸收法技术的脱氯效果、机理和优缺点,并针对吸附法脱氯效率不足、吸附剂损耗大和吸收法操作条件繁琐、二次污染风险高等问题提出研究与发展方向。     

Fast and clean dechlorination of alkyl and aryl (poly)chlorides catalysed by bimetallic Ni–Al clusters in the presence of t‐BuOH

The dechlorination of alkyl and aryl (poly)chlorides is rapid and complete upon treatment with a new reduction system consisting of NaH as reagent, Ni–Al clusters as catalyst and t‐BuOH as catalytic co‐factor. The high efficiency of this combination is presumed to be due to the stabilization of the subnanometre nickel particles formed during reduction by the in‐situ‐generated alkoxide. Copyright © 2001 John Wiley & Sons, Ltd.     

Isolation and Characterization of Bacteria that Degrade Poly (Lactic Acid-Glycerol Ester)-Type Time-Release Electron Donors for Accelerated Biological Reductive Dechlorination

Hydrogen Release Compound (HRC^TM) is an important electron donor that has recently become available and is now becoming widely applied to the accelerated biological reductive dechlorination of chloroethenes such as tetrachloroethene (PCE) and trichloroethene (TCE). HRC is a benign poly(lactic acid-glycerol ester) specially formulated for the slow time-release of lactic acid. Lactic acid is then metabolized to hydrogen, which can be used in the reductive dechlorination of chloroethenes. To establish an advance diagnosis of the HRC addition effect for the bioremediation of polluted sites, 17 strains of HRC-degrading bacteria were isolated by liquid- and plate-culture methods. All these strains could grow on a basal medium containing purified HRC as the sole carbon source. The sequence analysis of the 16S rDNAs of 6 of the 17 strains shows that they all belong to the family β-Proteobacteria, which includes Burkholderia cepacia, Burkholderia vietnamiensis, Ralstonia sp., and Variovorax paradoxus. The time course of HRC degradaton by strains JM-11, JM-12 and JM-13 showed that the HRC degradation rates after 9 days of cultivation were 81.1%, 82.8% and 80.4%, respectively. Preliminary assay of the activities of the HRC-degrading enzyme indicated that HRC degradation may be specifically performed by specific lipases produced by HRC-degrading microorganisms.     

Dechlorination of poly(vinyl chloride) by 1-butyl-3-methylimidazoliumhydroxide

Highly efficient dechlorination of PVC has been realized at 180 °C and at atmospheric pressure, using 1-butyl-3-methylimidazoliumhydroxide ([Bmim]OH) as an environment-friendly reaction medium: in the absence of an external base or solvent the dechlorination efficiency is as high as 91.2%, while it is only 38.1% for PVC without ionic liquids. The dechlorination process follows first-order kinetics with apparent activation energy of 44 kJ mol⁻¹. Mechanistic analysis provides evidence for the equilibrium presence of carbene species, together with the hydroxide ions in [Bmim]OH, thus enhancing the dechlorination of PVC via a combined elimination and substitution mechanism.     

The synthesis of substituted [1]benzothieno[2,3-c]quinolines and their N-methyl quaternary salts

Four substituted [1]benzothieno[2,3-c]quinolines 14a-14d were prepared by photocyclization of the appropriate carboxamides 8a-8d to the corresponding [1]benzothieno[2,3-c]quinolin-6(5H)-ones 12a-12d followed by chlorination to 6-chloro[1]benzothieno[2,3-c]quinolines 13a-13d and dechlorination resulting in the title compounds. Treatment of 14a-14d with iodomethane furnished the corresponding N-methyl quaternary salts 5a-5d .     

氧化镁对聚丙烯/聚氯乙烯脱氯行为的影响

对废旧塑料的回收利用是近年来人们一直关注和不断研究的一个重要课题。将废塑料热裂解为燃料油或单体被认为是最具前景的处理方法之一[1]。当含有PVC的废旧塑料裂解时产生氯化氢气体,严重腐蚀设备;同时也会产生含氯的有机化合物,从而使其裂解生成的液体作为燃料使用时会生成有     

Selective multiple magnesiations of the thieno[3,2-b]thiophene scaffold

A full functionalization of all four positions of the thieno[3,2‐b]thiophene scaffold was achieved. Starting from 2,5‐dichlorothieno[3,2‐b]thiophene, magnesiation of the 3‐ and 6‐position using tmpMgCl?LiCl furnishes, after trapping with various electrophiles, 3,6‐difunctionalized dichlorothieno[3,2‐b]thiophenes. Subsequent dechlorination and regioselective metalation or regioselective magnesium insertion into the C? Cl bond provides fully functionalized thieno[3,2‐b]thiophenes. Furthermore, new condensed heterocycles and small oligomers of these compounds with potential applications in material chemistry have been prepared.     

Dechlorination behaviour of flexible poly(vinyl chloride) in NaOH/EG solution

Flexible poly(vinyl chloride) (PVC) was found to be dechlorinated in NaOH/ethylene glycol (EG) solution at moderate temperature and at atmospheric pressure. The degree of dechlorination increased over time with all particle sizes and with decreasing particle size. Decreased particle size resulted in an increased effective surface area, increasing the contact between the material and OH⁻ in the NaOH/EG solution, which contributed to the high degree of dechlorination. The dechlorination of flexible PVC in NaOH/EG solution was expressed as a first-order reaction and proceeded under chemical reaction control. Diisononyl-phthalate (DINP) in the flexible PVC powder decomposed readily into phthalic acid and isononyl alcohol in a short time. For the dechlorination of the flexible PVC, the substitution (S_N2) of chloride by the hydroxyl group was considered to be preferential to the elimination (E2) of hydrogen chloride.     

Unraveling the Mechanism and Regioselectivity of the B12‐Dependent Reductive Dehalogenase PceA

PceA is a cobalamin‐dependent reductive dehalogenase that catalyzes the dechlorination of perchloroethylene to trichloroethylene and then to cis‐dichloroethylene as the sole final product. The reaction mechanism and the regioselectivity of this enzyme are investigated by using density functional calculations. Four different substrates, namely, perchloroethylene, trichloroethylene, cis‐dichloroethylene, and chlorotheylene, have been considered and were found to follow the same reaction mechanism pattern. The reaction starts with the reduction of Co^II to Co^I through a proton‐coupled electron transfer process, with the proton delivered to a Tyr246 anion. This is followed by concerted C?Cl bond heterolytic cleavage and proton transfer from Tyr246 to the substrate carbon atom, generating a Co^III?Cl intermediate. Subsequently, a one‐electron transfer leads to the formation of the Co^II?Cl product, from which the chloride and the dehalogenated product can be released from the active site. The substrate reactivity follows the trend perchloroethylene>trichloroethylene?cis‐dichloroethylene?chlorotheylene. The barriers for the latter two substrates are significantly higher compared with those for perchloroethylene and trichloroethylene, implying that PceA does not catalyze their degradation. In addition, the formation of cis‐dichloroethylene has a lower barrier by 3.8 kcal mol^?1 than the formation of trans‐dichloroethylene and 1,1‐dichloroethylene, reproducing the regioselectivity. These results agree quite well with the experimental findings, which show cis‐dichloroethylene as the sole product in the PceA‐catalyzed dechlorination of perchloethylene and trichloroethylene.     

Radiation-induced dechlorination of hexachlorobenzene

A study on radiation-induced dechlorination of hexachlorobenzene in alkaline ethanol solution was performed. At the beginning a higher efficiency for dechlorination has been found. The dechlorination is a chain reaction. The solubility of radiolytic products in ethanol-water (v/v 1:4) is higher than that of HCB in the same solvent. Hexachlorobenzene could be transfered into the solution and degraded partially if the soil contaminated by hexachlorobenzene was mixed with ethanol, then irradiated with γ-rays.