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[en] The results of the ring opening reaction of N-protected-cis-2-vinyl-3-(benzyloxymethyl)aziridines as model compounds for cis-3-substituted-2-vinylaziridines with various heteroatom nucleophiles are summarized in Table 1. Methanol is a good nucleophile to provide the desired 1,2-amino-alcohol derivative as a single product in excellent yield. We analyzed briefly the effect of solvents with methanol. Although other solvents such as DMF and THF also gave the product, CH2Cl2 was employed as a preferred solvent because of the high yield and ease of handling. All the reactions were, therefore, examined in CH2Cl2 in the presence of BF3·OEt2 as a Lewis acid unless mentioned otherwise. All alcohols behaved as good nucleophiles to exclusively give the desired products (entry 1-7)
[en] 1,3,5-Trichlorobenzene (TCB) was completely dechlorinated to benzene in a model reaction with magnesium and n-butylamine at room temperature in a ball mill. A full mass balance was observed for its stepwise reductive dechlorination via the intermediates 1,3-dichlorobenzene (DCB) and monochlorobenzene (MCB). This mechanochemical (MC) reaction occurred due to ongoing, simultaneous comminution and mechanical activation of small particle size magnesium during milling. The base metal was utilized as the actual dechlorinating agent whereas n-butylamine as a hydrogen donor. (author)
[en] A kinetic model for the electrochemical dechlorination of polychlorinated biphenyls (PCBs) will be an important contribution to the design and optimization of a continuous reactor. Initially, the electrocatalytic hydrodechlorination of 2-chlorobiphenyl (2-ClBP) to biphenyl at a palladium-modified nickel foam (Pd/Ni) cathode in a batch reactor was used as a model reaction for a quantitative study of the influences of the operating parameters, including temperature, the initial concentrations of PCBs, current density and the amount of Pd loading, on the apparent reaction rate. The dechlorination was found to follow pseudo first-order kinetics with respect to the 2-ClBP concentration. It was also found that a simple global power law rate equation, with Arrhenius dependency, can be used to describe the correlation between the pseudo first-order reaction rate constants and the reaction conditions. Subsequently, a mathematical model for predicting the performance of reductive dechlorination of 2-ClBP on Pd/Ni electrodes in a continuous stirred tank reactor was constructed, based on the batch-reaction kinetics. The suitability of the model was validated by performing experiments in and out of the range of reaction conditions applied in the batch reactor. The results show that the calculated values are a good fit to the experimental data
[en] Polychlorinated biphenyl (PCB) congeners (PCB 52, 77, and 153) singly and in mixture were spiked and aged in soil microcosms and subsequently planted with switchgrass (Panicum virgatum) or poplar (Populus deltoids x nigra DN34). The planted reactors showed significantly greater reductions in PCB parent compounds when compared to unplanted systems after 32 weeks. There was evidence of reductive dechlorination in both planted and unplanted systems, but the planted microcosms with fully developed roots and rhizospheres showed greater biotransformation than the unplanted reactors. These dechlorination products accounted for approximately all of the molar mass of parent compound lost. Based on the transformation products, reductive dechlorination pathways are proposed for rhizospheric biotransformation of PCB 52, 77, and 153. This is the first report of rhizosphere biotransformation pathways for reductive dechlorination in marginally aerobic, intermittently flooded soil as evidenced by a mass balance on transformation products. -- Highlights: •Soil was spiked and aged and then planted with poplar and switchgrass. •Planted microcosms showed significant reductive dechlorination and greater biotransformation than unplanted reactor. •Rhizospheric reductive dechlorination pathways are proposed. -- This study provides insight into rhizospheric transformation of PCBs
[en] Polychlorinated biphenyls (PCBs) were widely used as insulator fluids in electrical equipment, early in the 20th century, but were banned for use about 25 years ago due to their potential toxicity. However, they are still in storage, or present as equipment and soil contaminants, and their safe disposal remains a major challenge. On gamma irradiation in alkaline 2-propanol solutions, PCBs (Arochlor 1254 and 1016) dechlorinate stepwise, giving biphenyl as the ultimate product. Irradiation of alkaline 2-propanol solutions leads to the formation of acetone anion, which transfers electron to PCBs, and partially dechlorinated PCBs, dechlorinating them by one chlorine atom at a time and producing acetone and chloride anion. Acetone, biphenyl and oxygen inhibit the dechlorination of the PCBs. This method has the potential to be used on large scale for the dechlorination of PCBs and PCB-contaminated equipment (capacitors and transformers)
[en] Pyrochemical process to recover uranium and transuranic elements from the spent nuclear fuel indispensably generates radioactive metal chlorides waste containing fission products. These wastes are difficult to solidify and stabilize by conventional method due to their volatility and low comparability with silicate glass. Our research group is under development of dechlorination method to remove Clinduced problems. For dechlorination of metal chloride waste, an inorganic composite, SiO2-Al2O3-P2O5 (SAP), has been investigated as dechlorination agent. The composite reacts with metal chloride to produce aluminosilicates, alumino phosphate and orthophosphate. The products are thermally stable up to 1200 .deg. C and compatible with silicate glass. In this study, modified SAP containing Fe2O3 as another component was investigated to enhance the dechlorination reaction and characterize the reaction behavior of LiCl
[en] Highlights: • TCBPA can be rapidly and completely dechlorinated by Pd/Fe bimetallic catalysts. • The observed rate constants are functions of dosages, initial concentration, Pd coverage and solution pH. • Pd dosage is the major factor in the observed rates of the reaction. • This is the first report investigating the dechlorination of TCBPA by Pd/Fe catalysts. -- Abstract: The Pd/Fe bimetallic catalysts of micron sizes were synthesized and the rates of tetrachlorobisphenol A (TCBPA) degradation were measured under various conditions using a batch reactor system. The results showed that TCBPA was rapidly dechlorinated to tri-, di- and mono-chlorobisphenol A and to bisphenol A (BPA). The observed rate constants (kobs) were found to increase as functions of the Pd coverage on the Fe particles and the dosages of the catalysts within the reactors. The kobs value decreased as the initial TCBPA concentration increased, suggesting that the TCBPA dechlorination may follow a surface-site limiting Langmuir–Hinshelwood rate model. The weakly acidic solution, especially at or near pH 6.0, also favored the dechlorination of TCBPA. At pH 6.0, Pd coverage of 0.044 wt% and catalyst dosage of 5 g L−1, TCBPA with an initial concentration of 20 μM was completely transformed within 60 min, and BPA was detected as the major product through the reaction time. Meanwhile, the kobs values measured at constant solution pH correlated linearly with the mass of particle-bound Pd introduced to the reactors, regardless of Pd/Fe catalyst dosage or Pd surface coverage. This study suggested that Pd/Fe catalysts could be potentially employed to rapidly degrade TCBPA in the contaminated environment
[en] Diclofenac (DCF) is one of the most widely used non-steroidal anti-inflammatory drugs worldwide, and several studies have reported adverse effects on the environment, in plants and animals; so, it is classified as an emerging pollutant. There are several alternatives for its removal; however, it is necessary to study the way in which the DCF is degrading to offer more effective removal techniques, since the traditional ones such as chlorination, activated sludge, and biofiltration offer low removal efficiency (20–40%). This work analyzes the kinetic behavior of the photodegradation of DCF and the thermodynamic parameters of the reaction under UV-C-type light radiation. The results obtained indicate that it presents a first-order kinetic promoted by the increase of the temperature. Also, within the evaluated interval (273 to 308 K), the values of the kinetic coefficient (k) range between 0.05 and 0.20 min−1 and the half-life ranges from 3 to 9 min. The reaction is exothermic and spontaneous and gives way to the formation of approximately 6 byproducts, being two with the greatest presence and stability. This suggests that its decomposition route occurs through the dechlorination of the molecule and originate compounds known as carbazoles that have been detected in previous works. It was also found that this mixture of byproducts remained after the degradation of the drug, which is released to the environment, so it is necessary to extend a study on its properties and its possible environmental impact.
[en] The degradation characteristics of clopyralid irradiated by electron beam (EB) was studied in aqueous solutions. The effects of factors, such as initial clopyralid concentrations, addition of radicals scavenger, initial solution pH and addition of H2O2, were investigated on clopyralid degradation efficiency and mechanism. It was found that the EB-radiolysis was an effective way to degrade clopyralid and its degradation rate decreased with the increasing of substrate concentration. In the investigated initial concentrations range of 100-400 mg L-1, the radiolytic degradation of clopyralid followed a pseudo-first kinetic order. The results from addition of radicals scavenger indicated that both ·OH and eaq- played significant roles in the degradation of clopyralid. Furthermore, the alkaline condition and addition of H2O2 (<10 mM) in the solution also slightly enhanced the efficiency of clopyralid degradation. The ion chromatography analysis showed that some organic acids (formic acid, acetic acid and oxalic acid) were formed, while the completely dechlorination of the substrate was achieved and organic nitrogen was recovered in the form of ammonium and nitrate ions during the irradiation process. (author)
[en] Enhanced reductive dehalogenation is an attractive treatment technology for in situ remediation of chlorinated solvent DNAPL source areas. Reductive dehalogenation is an acid-forming process with hydrochloric acid and also organic acids from fermentation of the electron donors typically building up in the source zone during remediation. This can lead to groundwater acidification thereby inhibiting the activity of dehalogenating microorganisms. Where the soils' natural buffering capacity is likely to be exceeded, the addition of an external source of alkalinity is needed to ensure sustained dehalogenation. To assist in the design of bioremediation systems, an abiotic geochemical model was developed to provide insight into the processes influencing the groundwater acidity as dehalogenation proceeds, and to predict the amount of bicarbonate required to maintain the pH at a suitable level for dehalogenating bacteria (i.e., > 6.5). The model accounts for the amount of chlorinated solvent degraded, site water chemistry, electron donor, alternative terminal electron-accepting processes, gas release and soil mineralogy. While calcite and iron oxides were shown to be the key minerals influencing the soil's buffering capacity, for the extensive dehalogenation likely to occur in a DNAPL source zone, significant bicarbonate addition may be necessary even in soils that are naturally well buffered. Results indicated that the bicarbonate requirement strongly depends on the electron donor used and availability of competing electron acceptors (e.g., sulfate, iron (III)). Based on understanding gained from this model, a simplified model was developed for calculating a preliminary design estimate of the bicarbonate addition required to control the pH for user-specified operating conditions.