Complete Debromination Research Articles

Complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether by visible-light photocatalysis on g-C3N4 supported Pd

Deep debromination of polybrominated diphenyl ethers (PBDEs) by visible light photocatalysis is still a challenge in the field of halogenated pollutants control. Here, an efficient photocatalyst (Pd/g-C3N4) was prepared by a simple impregnation-chemical reduction method with bulk g-C3N4 and PdCl2 as precursors. Under preferred reaction conditions (visible light irradiation for 120 min), the use of the 0.5% Pd/g-C3N4 composites (0.4 g L−1) yielded an almost complete debromination of BDE47 (10 μmol L−1) in methanol-water mixture, while the debromination of BDE47 did not occur on pure g-C3N4. A “Pd-promoted active H atom species attack and C-Br bond cleavage” route was proposed according to the identified degradation intermediates. A catalytic mechanism was further clarified: Pd nanoparticles exerted affinity interaction with bromine atoms, and the storing of electrons on Pd would increase the binding interaction. In the debromination process, methanol acts as both a hole scavenger and a hydrogen donor to provide active H atom species through the reaction of H+ and photogenerated electrons on Pd nanoparticles. The initiation of BDE47 debromination on Pd nanoparticles required an induction period to enrich a critical amount of electrons for stretching the C-Br bond and its subsequent being attacked by active H atoms. The generated 2,2′-dibromodiphenyl ether (BDE4) would be further reduced to bromine-free products by hydro-debromination process or coupling reaction.

A novel management strategy for removal and degradation of polybrominated diphenyl ethers (PBDEs) in waste printed circuit boards

Waste printed circuit boards (PCBs) contain a high level of brominated flame retardants (BFRs), among which polybrominated biphenyl ethers (PBDEs) are the most widely used additive BFRs. PBDEs are considered to be a type of persistent organic pollutants (POPs). The efficient removal/degradation of PBDEs in waste PCBs is an urgent problem in electronic waste treatment, but the degradation of PBDEs is a great challenge due to their extreme stability and persistence in nature. In this study, a novel management strategy was developed for removal and degradation of PBDEs in waste PCBs by using a simple subcritical methanol (SubCM) process. The results showed that reaction temperature, residence time, solid-to-liquid ratio, and additive NaOH are key factors influencing the removal of PBDEs from waste PCBs. Under optimal conditions (200 °C, 60 min, 1:20 g/mL), the removal efficiency of ∑8PBDEs from waste PCBs could reach 91.3% and 98.8% for the proposed process of SubCM and SubCM + NaOH, respectively. When the temperature is below 200 °C, highly brominated PBDEs congeners in waste PCBs were degraded into 2,'3,4′,6-Tetrabromodiphenyl ether (BDE71) and 2,4,4′-Tribromodiphenyl ether (BDE28) after SubCM treatment. 4-Bromophenyl ether (BDE4) and diphenyl ether were generated by the further debromination of BDE71 and BDE28 with the increase of treatment temperature. The debromination temperature of PBDEs congeners in SubCM could be markedly lowered by adding 4 g/L of NaOH. The complete debromination of PBDEs congeners in waste PCBs could be achieved at 300 °C and 250 °C for the developed process of SubCM and SubCM + NaOH, respectively.

Ion chromatographic determination of total bromine in electronic devices in conjunction with a catalytic reduction debromination pretreatment

A new determination method for total bromine in electronic devices was developed by using ultrasound assisted extraction, copper-catalyzed reductive debromination and ion chromatography (UAE-RD-IC). It was found that all the added brominated flame retardants (polybrominateddiphenyl ethers, polybrominated biphenyls, tetrabromobisphenol A, and hexabromocyclododecane) could be completely debrominated by using copper-based catalysts and reducing agent N2H4•H2O. The complete debromination of brominated flame retardants released all of their bromine in the form of bromide ions, which could be determined by ion chromatography. After the extraction parameters were optimized by achieving the maximum IC signal in the certified reference material GBW(E) 082725, the UAE-RD-IC method was established for the determination of total bromine in solid samples. By analyzing the certified reference material, the Br content was obtained as 695.3 ± 16.0 mg kg−1, being well consistent with its standard value (694.54 ± 30.63 mg kg−1). The relative standard deviation (RSD) of five parallel determinations was 1.7%, indicating the good repeatability of the developed method. The proposed method was further applied to analyze the samples of cables and computer mouse shells. For all these practical samples, the Br contents obtained by the UAE-RD-IC method were in good agreement with that obtained by the standard oxygen bomb combustion-IC method. It was noted that the new method has a detection limit of Br of about 20 mg kg−1, being much lower than that (75 mg kg−1) of the traditional oxygen bomb combustion-IC method for total bromine detection. Therefore, the proposed method was qualified as a practical method to measure total bromine content in actual electronic devices with good analytical performances of accuracy, precision and sensitivity.

Reductive debromination of tetrabromobisphenol A by tailored carbon nitride Fe/Cu nanocomposites under an oxic condition

Supple exfoliated graphitic carbon nitride (C3N4) with high electron transport and photoactive properties are utilized as catalyst supports for environmental remediation. This study synthesized Fe/Cu bimetallic catalyst decorated on to the C3N4 matrix as an excellent support for complete debromination of tetrabromobisphenol A (TBBPA), one emerging contaminant and also one brominated flame retardant, under oxic conditions. Fe/Cu bimetallic nanoparticles are deposited on few layered thick C3N4 (CN) matrices. XRD, SEM-EDS, EPMA and surface area analysis show that as synthesized Fe/Cu@CN nanocomposites contain well distributed zerovalent iron (ZVI) and Cu nanoparticles (NPs) with enhanced surface area. Fe/Cu@CN nanocomposites showed catalytic degradation of TBBPA under ambient conditions and byproducts were analyzed and identified by HPLC and GC-MS respectively. Various factors such as catalyst dose, initial TBBPA concentration, and initial pH condition were executed to optimize the best conditions for the rapid and complete degradation of TBBPA. The highest degradation rate of 0.191 min−1 was recorded by Fe/Cu@CN nanocomposites under neutral pH and ambient conditions. Furthermore, the electrochemical impedance spectroscopic analysis revealed that C3N4 matrix plays a crucial role during the degradation process by providing large surface area, excellent electron transportability for wrapped Fe/Cu bimetallic NPs, resulting in reduced inherent iron corrosion. This study discloses that C3N4 is a promising catalyst support with restricted iron corrosion paving the way to tailor the Fe0 based nanocomposites in elucidation of wide variety of catalytic and photocatalytic reduction applications.

Kinetics and mechanisms of debromination of tetrabromobisphenol A by Cu coated nano zerovalent iron

Brominated flame retardants are of concern to our environment because of its endocrine disruptive, immune toxicant characteristics, and toxic brominated byproducts. As a potential remediation technology, debromination of tetrabromobisphenol A (TBBPA) from both aqua and soil by Cu coated nano zero-valent iron particles (Cu-nZVI) was investigated. Because of its catalytic reductive properties, Cu-nZVI has a potential for removing TBBPA. Batch experiments show that Cu-nZVI effectively debrominated TBBPA into tri-, di-, mono-bromobisphenol A, and bisphenol A (BPA) with a low suspension density (0.5 g L−1). As indicated by the low apparent activation energy (69.66 kJ mol−1), the optimal reaction condition was the Cu loading of 0.5 wt%, 27 °C and pH 5.0. Tetrabromobisphenol A (10 mg L−1) was transformed into several reaction products within 120 min, and BPA was detected as a major reaction product after 240 min. The reaction rate constant (kobs) was proportionally correlated to solid-solution ratio and temperature. The concentration of metals during the debromination was too low (less than 0.13 mg L−1) to induce an adverse effect on the ecosystem. During the redox reaction, a new mineral, magnetite formed on particles’ surface accompanied by the oxidation of Fe0 and the elevation of pH. This study suggests that Cu-nZVI has the potential to be explored for the rapid and complete debromination of brominated flame retardants in both aquatic and edaphic environments.

Ligand directed debromination of tetrabromodiphenyl ether mediated by nickel under visible irradiation

Complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether catalysed by in situ formed, trimethylamine coordinated Ni. The amine coordination is essential for the high debromination degree.

Ultrarapid and Deep Debromination of Tetrabromodiphenyl Ether over Noble-Metal-Free Cu/TiO2 Nanocomposites under Mild Conditions.

Fast and deep debromination of polybrominated diphenyl ethers (PBDEs) under mild conditions is a challenge in the field of pollution control. A strategy was developed to achieve it by exploiting Cu/TiO2 composites as a noble-metal-free catalyst. Toward the debromination of 2,2',4,4'-tetrabromodiphenyl ether (BDE47) as a typical PBDE, the use of Cu/TiO2 as a catalyst and hydrazine hydrate (N2H4·H2O) as a reducing agent yielded a degradation removal of 100% and a debromination efficiency of 87.7% in 3 s. A complete debromination of BDE47 at 1500 mg L-1 was possible by successively adding N2H4·H2O. A debromination pathway involving active H atom species was proposed for the catalytic transfer hydrogenation (CTH) of PBDEs according to the identified degradation intermediates. A mechanism was further clarified by density functional theory calculations: electrons are delivered from N2H4·H2O to the metallic Cu atom via a coordination of N in N2H4·H2O with Cu atoms. The electron-trapped Cu atom interacts with adsorbed BDE47 to form a transition complex, and then the debromination of this complex occurs on the surface of Cu nanoparticles due to the hydrogen donation of N2H4·H2O through the CTH process. The new method provides a highly efficient method to remove brominated pollutants.

Sonoelectrochemical Reduction of Tetrabromobisphenol-a at Silver Cathodes in Dimethylformamide

First reported in the early 1930s, sonoelectrochemistry is an analytical technique that seeks to incorporate ultrasound into electrochemical experiments. Compton and co-workers reviewed the numerous advantages of sonoelectrochemistry over “silent” experiments without ultrasound, including increased mass transport and electrode surface roughening.1 Presently, there is a lack of research employing sonoelectrochemistry to study environmental remediation, a topic of particular interest in our group. As a beginning inquiry into the various factors that optimize sonoelectrochemical reduction, a comparative study into the reduction of the flame retardant 3,3',5,5'-tetrabromobisphenol-A (TBBPA) was undertaken with the aid of cyclic voltammetry, controlled-potential (bulk) electrolysis, and sonoelectrochemistry. Cyclic voltammograms of TBBPA at silver cathodes in dimethylformamide containing 0.10 M tetramethylammonium tetrafluoroborate (TMABF4) show three irreversible cathodic peaks with peak potentials of –0.50 V, –0.70 V, and –1.34 V versus a cadmium-saturated mercury amalgam reference electrode (Cd(Hg)). However, bulk electrolyses of TBBPA at –1.50 V versus Cd(Hg) under the same conditions show minimal debromination as a result of competitive reduction pathways between the carbon–bromine bonds and the phenolic hydrogens within the molecule. To improve debromination, two alternate pathways are explored: the methylation of TBBPA (MeTBBPA) to prevent O–H reduction and the introduction of ultrasound to electrochemical analysis. Cyclic voltammograms of MeTBBPA show two irreversible cathodic peaks (–0.70 V and –0.90 V versus Cd(Hg)) and bulk electrolyses at –1.50 V versus Cd(Hg) show complete debromination in TMABF4–DMF. Similarly, sonoelectrochemical bulk electrolysis experiments at –1.50 V vs. Cd(Hg) show a substantial increase in debromination compared to electrolyses under “silent” conditions. 1 R. G. Compton, J. C. Eklund, F. Marken, Electroanalysis 1997, 9, 509–522.

Diversity and Dynamics of Microbial Community Structure in Different Mangrove, Marine and Freshwater Sediments During Anaerobic Debromination of PBDEs.

Little is known about the diversity and succession of indigenous microbial community during debromination of polybrominated diphenyl ethers (PBDEs). This study examined the diversity and dynamics of microbial community structure in eight saline (mangrove and marine) and freshwater sediment microcosms exhibiting different debrominating capabilities for hexa-BDE 153, a common congener in sediments, using terminal restriction fragment length polymorphism (T-RFLP) and clone library analyses. The results showed that microbial community structure greatly differed between the saline and freshwater microcosms, likely leading to distinct variations in their debrominating capabilities and pathways. Higher relative abundances of Chloroflexi and Deltaproteobacteria succeed by Alphaproteobacteria and Betaproteobacteria were detected in the two mangrove microcosms with the fastest debrominating capabilities mainly via para pathway, respectively; the dominance of Alphaproteobacteria resulted in less accumulation of tetra-BDEs and more complete debromination of lower brominated congeners (from di- to tetra-BDEs). Meanwhile, the shifts in both microbial community structure and PBDE profiles were relatively small in the less efficient freshwater microcosms, with relatively more ortho and meta brominated products of BDE-153 resulted. Coincidently, one of the freshwater microcosms showed sudden increases of Chloroflexi and Deltaproteobacteria by the end of incubation, which synchronized with the increase in the removal rate of BDE-153. The significant relationship between microbial community structure and PBDEs was confirmed by redundancy analysis (18.7% of total variance explained, P = 0.002). However, the relative abundance of the well-known dechlorinator Dehalococcoides showed no clear correlation with the debrominating capability across different microcosms. These findings shed light in the significance of microbial community network in different saline environments on enhancement of PBDE intrinsic debromination.

A one-pot consecutive photocatalytic reduction and oxidation system for complete debromination of tetrabromodiphenyl ether

Polybrominated diphenyl ethers (PBDEs) are a family of important organic pollutants, and methods for their complete debromination are urgently needed. It is known that highly-brominated PBDEs are easily photocatalytically reduced to lower-brominated congeners, and the lower-brominated congeners are relatively susceptible to photocatalytic oxidation but not to further reduction. The present work developed a one-pot photocatalytic consecutive reduction and oxidation method (O-CRO) for the complete debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47). It was observed that BDE47 was resistant to photocatalytic reduction on TiO2 but underwent a slow oxidation in aerobic aqueous solutions (rate constant k = 0.065 h−1). The use of a reduced graphene oxide and TiO2 (RGO/TiO2) composite only slightly improved the photocatalytic oxidation of BDE47 in air-H2O systems (k = 0.12 h−1), but achieved a rapid photocatalytic reduction of BDE47 (k = 0.81 h−1) in anoxic ACN-H2O systems; however, the debromination was only 25.0% even after 14 h because the reduction intermediates (i.e., tri-BDEs) were minimally reduced. To conduct the O-CRO process, we developed an anoxic RGO/TiO2-H2O system containing a small amount of methanol. This system yielded the complete debromination and mineralization of BDE47 within 14 h. The mechanism for the debromination and mineralization of BDE47 was clarified. This method overcame the drawbacks of the separated two-step reduction and oxidation method and will find promising applications for the degradation of halogenated organic pollutants.

Mechanochemical pre-treatment for viable recycling of plastic waste containing haloorganics

Chemical recycling technologies are the most promising for a waste-to-energy/material recovery of plastic waste. However, 30% of such waste cannot be treated in this way due to the presence of halogenated organic compounds, which are often utilized as flame retardants. In fact, high quantities of hydrogen halides and dioxin would form. In order to enabling such huge amount of plastic waste as viable feedstock for recycling, an investigation on mechanochemical pre-treatment by high energy ball milling is carried out on polypropylene containing decabromodiphenyl ether. Results demonstrate that co-milling with zero valent iron and quartz sand ensures complete debromination and mineralization of the flame retardant. Furthermore, a comparative experiment demonstrates that the mechanochemical debromination kinetics is roughly proportional to the polymer-to-haloorganics mass ratio.

Efficient debromination of Tetrabromobisphenol A (TBBPA) by Au/Fe@biocarbon derived from bioreduction precious metals

The utilization of nano zero valent iron is recognized as a potential approach for debromination of Tetrabromobisphenol A (TBBPA). In this study, Pycnoporus sanguineus cells were employed for biosupported Au nano particles (bio-AuNPs) preparation, then calcinated for obtaining porous carbon doped with Au nano particles (Au@biocarbon) and generated Au@biocarbon supported zero-valent iron nanoparticles (Au/Fe@biocarbon). The role of Au/Fe@biocarbon during debromination was evaluated by comparing with Au@biocarbon, biocarbon and Fe@biocarbon. Results showed that Fe0 and Au0 are successfully loaded on the surface of porous biocarbon with well-dispersion and higher specific surface area. The removal and debromination efficiency of TBBPA driven by Au/Fe@biocarbon was up to about 99.85% and 97.18% within 100min, respectively. Higher dosage and acidic condition were more beneficial to removal of TBBPA with the most appropriated Au/Fe molar ratio of 2%, where the complete removal of TBBPA only took 20min. The mechanism of TBBPA debromination by Au/Fe@biocarbon was the joint function of adsorption of biocarbon and galvanic cell of biosupported Au/Fe bimetals. Therefore, Au/Fe@biocarbon could be an alternative to effectively boost rapid and complete debromination of TBBPA.

Microbial degradation of the brominated flame retardant TBNPA by groundwater bacteria: laboratory and field study

In the present study, the biodegradation of the brominated flame retardant tribromoneopentylalcohol (TBNPA) by a groundwater enrichment culture was investigated using a dual carbon (13C/12C)- bromine (81Br/79Br) stable isotope analysis. An indigenous aerobic bacterial consortium was enriched from the polluted groundwater underlying an industrial site in the northern Negev Desert, Israel, where TBNPA is an abundant pollutant. Aerobic biodegradation was shown to be rapid, with complete debromination within a few days, whereas anaerobic biodegradation was not observed. Biodegradation under aerobic conditions was accompanied by a significant carbon isotope effect with an isotopic enrichment factor of ɛCbulk = −8.8‰ ± 1.5‰, without any detectable bromine isotope fractionation. It was found that molecular oxygen is necessary for biodegradation to occur, suggesting an initial oxidative step. Based on these results, it was proposed that H abstraction from the C-H bond is the first step of TBNPA biodegradation under aerobic conditions, and that the C-H bond cleavage results in the formation of unstable intermediates, which are rapidly debrominated. A preliminary isotopic analysis of TBNPA in the groundwater underlying the industrial area revealed that there are no changes in the carbon and bromine isotope ratio values downstream of the contamination source. Considering that anoxic conditions prevail in the groundwater of the contaminated site, the lack of isotope shifts in TBNPA indicates the lack of TBNPA biodegradation in the groundwater, in accordance with our findings.

Catalytic debromination of tetrabromobisphenol A by Ni/nZVI bimetallic particles

In this paper, nickel/nanoscale zero-valent iron (Ni/nZVI) bimetallic particles were explored for TBBPA degradation under ambient condition. Various factors such as Ni/nZVI loading (0.5, 1.0, 1.5, 2.0, and 3.0gL−1), initial TBBPA concentration (5, 10, 15, 20, and 30mgL−1), and initial solution pH (3.0, 5.0, 6.0, 7.0, 9.0, and 11.0) were tested in order to find the optimum conditions for rapid and complete degradation of TBBPA. The results showed that TBBPA could be degraded via pseudo first-order kinetics with respect to the Ni/nZVI loading and that the observed pseudo first-order rate constant (kobs) was found to decrease with the increasing of initial TBBPA concentration at constant Ni/nZVI loading. At initial concentration of 10mgL−1, nearly 100% TBBPA could be degraded within 120min by 2.0gL−1 Ni/nZVI with kobs reached up to 5.35×10−2min−1 at acidic to neutral pH. pH plays an important role during TBBPA debromination processes inherent to iron corrosion. Slightly acidic pH (5.0–6.0) was favorable for the complete debromination of TBBPA, with over 93% bisphenol A (BPA) formed during the experiment. Whereas under acidic (pH 3.0) or alkaline conditions (pH 9.0 and 11.0), the reaction kinetics were slower and partial debromination product dibromobisphenol A (di-BBPA) was dominant. This study suggested that under optimized conditions, Ni/nZVI could be effectively applied for rapid and complete debromination of TBBPA in handling of wastewater treatment.

A Novel Cathode Material for Cathodic Dehalogenation of 1,1-Dibromo Cyclopropane Derivatives.

Leaded bronze turned out to be an excellent cathode material for the dehalogenation reaction of cyclopropanes without affecting the strained molecular entity. With this particular alloy, beneficial properties of lead cathodes are conserved, whereas the corrosion of cathode is efficiently suppressed. The solvent in the electrolyte determines whether a complete debromination reaction is achieved or if the process can be selectively stopped at the monobromo cyclopropane intermediate. The electroorganic conversion tolerates a variety of functional groups and can be conducted at rather complex substrates like cyclosporine A. This approach allows the sustainable preparation of cyclopropane derivatives.

Complete debromination of decabromodiphenyl ether using the integration of Dehalococcoides sp. strain CBDB1 and zero-valent iron

This study investigated the effects of nano- and micro-scale zero-valent iron (nZVI and mZVI) particles on Dehalococcoides sp. strain CBDB1 participating in anaerobic reduction of polybrominated diphenyl ethers. nZVI (>0.25gL−1) had an inhibitory effect upon this strain, whereas 1.0gL−1 mZVI showed no negative impact on bacterial growth. Strain CBDB1 could only utilize lower brominated congeners (<7 bromines) as electron acceptor. In the bio-ZVI system, decabromodiphenyl ether (BDE-209) was first reduced by ZVI to lower brominated congeners, which were then dehalogenated to diphenyl ether by CBDB1. Within 30 d, a BDE-209 debromination efficiency of 16% and 24% was obtained in the bio-nZVI (0.25gL−1) and bio-mZVI (1.0gL−1) systems with a corresponding diphenyl ether yield efficiency of 14% and 19%, respectively. The debromination efficiency increased significantly from 8% to 24% with an increase of mZVI dosage from 0.25 to 1.0gL−1 in the bio-mZVI system.

Enhanced degradation of Tetrabromobisphenol A in water by a UV/base/persulfate system: Kinetics and intermediates

Tetrabromobisphenol A (TBBPA), one of the most frequently used brominated flame retardants (BFRs), is only soluble in strongly alkaline solutions where most advanced oxidation processes (AOPs) are inefficient or in organic solvents. It is highly desirable to develop an environmentally friendly cleanup technology for TBBPA which operates at alkaline pH without the need of organic solvents to enhance its solubility in water. In this study a favorable UV/base/persulfate (PS) system for rapid degradation of TBBPA in aqueous solution is reported. Increases of initial pH and PS concentrations have positive effects on the degradation of TBBPA and a high initial TBBPA concentration has a negative influence. The addition of Br− has a negligible effect on the degradation of TBBPA. The low TOC removal and degradation intermediates of TBBPA identified by GC–MS suggested that TBBPA was degraded via the cleavage between the isopropyl group and one of the benzene rings rather than complete debromination and degradation. The present study provides a simple and green approach to detoxify TBBPA in water rather than using toxic organic solvents.

A new method for functionalizing α,γ‐dinitro compounds at the β‐position: application to the cyclization of β‐alkoxy‐α,γ‐dinitro compounds

Treatment of 2,4‐dinitropentane with bromine and sodium methoxide in methanol, affords formation of an ether product, 2,4‐dibromo‐3‐methoxy‐2,4‐dinitropentane, in 59% yield as a mixture of three diastereomers. This observation has led to a general synthesis of 3‐alkoxy‐2,4‐dibromo‐2,4‐dinitropentanes, obtained in 75‐86% yield from 2,4‐dibromo‐2,4‐dinitropentane as the preferred reactant. 4‐Bromo‐2,4‐dinitro‐2‐pentene has been identified as an intermediate in these reactions. The nitroalkene has been isolated and undergoes conjugate addition with alkoxides to afford the same ether products after brominative work‐up. The nitroalkene undergoes conjugate addition with sodium azide to give 3‐azido‐2,4‐dibromo‐2,4‐dinitropentane in 38% yield as a mixture of two isomers in which the (R*,R*) isomer predominates. Sequential treatment of 2,4‐dibromo‐2,4‐dinitropentane with sodium methoxide followed by sodium iodide and acetic acid gives 3‐methoxy‐2,4‐dinitropentane in 63% yield, the overall product of simple methoxylation of 2,4‐dinitropentane. However, attempted complete debromination of 2,4‐dibromo‐3‐methoxy‐2,4‐dinitropentane with excess sodium iodide and acetic acid results only in monodebromination to give 2‐bromo‐3‐methoxy‐2,4‐dinitropentane in 86% yield. Likewise, 2‐bromo‐3‐ethoxy‐2,4‐dinitropentane is formed in 93% yield from the ethoxy analog. A mechanistic rationale is offered for condition‐specific removal of the second Br atom in these reactions. Treatment of 3‐methoxy‐2,4‐dinitropentane with potassium acetate/iodine in dimethyl sulfoxide affords formation of 4,5‐dihydro‐3,4‐dimethyl‐3‐methoxy‐4‐nitroisoxazole 2‐oxide in 30% yield as a single diastereomer. Conversion of 2‐bromo‐3‐methoxy‐2,4‐dinitropentane in 15% yield to 4,5‐dihydro‐3,4‐dimethyl‐3‐methoxy‐4‐nitroisoxazole 2‐oxide is also possible by using potassium acetate in dimethyl sulfoxide. The mechanistic pathways for formation of 4,5‐dihydro‐3,4‐dimethyl‐3‐methoxy‐4‐nitroisoxazole 2‐oxide apparently involve unstable 3‐methoxy‐1,2‐dimethyl‐1,2‐dinitrocyclopropane as the common intermediate. Similarly, 2‐bromo‐3‐ethoxy‐2,4‐dinitropentane affords 4,5‐dihydro‐3‐ethoxy‐3,4‐dimethyl‐4‐nitroisoxazole 2‐oxide in 13% yield. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Application of Low-Cost Sponge Iron for Complete Debromination of Polybrominated Diphenyl Ethers

Application of Low-Cost Sponge Iron for Complete Debromination of Polybrominated Diphenyl Ethers

Electrochemical reduction of decabromodiphenyl ether at carbon and silver cathodes in dimethylformamide and dimethyl sulfoxide

An investigation of the electrochemical reduction of the flame-retardant, decabromodiphenyl ether (DBDE), at carbon and silver cathodes has been undertaken with the aid of cyclic voltammetry and controlled-potential (bulk) electrolysis in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), each solvent containing 0.10M tetra-n-butylammonium tetrafluoroborate (TBABF4). Cyclic voltammograms for reduction of DBDE at a glassy carbon electrode exhibit five irreversible and comparably sized cathodic peaks that are associated with a sequence of debromination processes, whereas cyclic voltammograms acquired with a silver cathode show fewer discrete stages of irreversible reduction and are accentuated by one very prominent peak. Bulk electrolyses of DBDE at either a reticulated vitreous carbon or a silver cathode in DMF lead to approximately 20–25% conversion of DBDE to a mixture of diphenyl ether, dibenzofuran, benzene, and phenol, and the remaining products are congeners of dibromodiphenyl ether. When DMSO is employed as solvent for bulk electrolyses, diphenyl ether is formed in approximately 20% yield, and a mixture of congeners ranging from decabromo- to monobromodiphenyl ether is found. Bulk electrolyses of DBDE in DMF–TBABF4 at carbon held at a potential near the cathodic limit indicate that complete debromination can be achieved.