Ultrasonic-enhanced Stereoselective Debromination of vic-Dibromides to Alkenes with Metallic Zinc Powder in Aqueous Media

Carbon-carbon double bond functional groups are often protected through a popular bromination/debromination method because of their reactivity. An ultrasonic-enhanced stereoselective debromination of vic-dibromides with metallic zinc powder in aqueous media has been developed, which generates E-alkenes with excellent yields. The reactivity of vic-dibromides decreases in the order of 1,2-dibromo-1,2-diphenylethane>1,2-dibromo-1-phenylethane>1,2-dibromo-1,2-dialkylethane.

Efficient Debromination of Vicinal a, b-Dibromo Carboxylic Acid Derivatives with the Sm/HOAc System

The ? ?vicinal dibromo carboxylic acid and its derivatives were debrominated with Sm/HOAc system to afford the corresponding cinnamic acid and its derivatives in good yields under mild conditions.

CATALYTIC DEBROMINATION OF DIPHENYL BROMOMETHANE UNDER HETEROPHASE CONDITIONS USING POLYMERS WITH VIOLOGEN STRUCTURE

The debromination of diphenyl bromomethane (Ph_2CHBr) using polymers with viologen structure as electron--transfer catalyst (ETC) afforded tetraphenylethane in good yields under het- erophase conditions.

EPR STUDIES ON THE DEBROMINATION OF DIPHENYL BROMOMETHANE IN THE PRESENCE OF VIOLOGEN DERIVATIVES AS ELECTRON-TRANSFER CATALYSTS (ETC)

The active intermediate'carbon radical' was detected by the spin—trapping reagent (POBN) during the debromination of Ph_2CHBr in the presence of viologen derivatives as electron—transfer catalysts(ETC).

A FACILE METHOD FOR DEBROMINATION OF VICINAL DIBROMIDES

In the presence of equimolar triethylamine,vicinal dibromides were found to be easily debrominated by dibutyl telluride,forming the co- rresponding olefins.

A FACILE METHOL FOR THE DEBROMINATION OF BROMOCARBONYL COMPOUNDS WITH DIBUTYL TELLURIDE

(?)-bromocarbonyl compounds can be debrominated with dibutyl telluride in the presence of triethylamine in high yields.

Uptake, translocation, and debromination of polybrominated diphenyl ethers in maize

Uptake, translocation and debromination of three polybrominated diphenyl ethers （PBDEs）, BDE-28, -47 and -99, in maize were studied in a hydroponic experiment. Roots took up most of the PBDEs in the culture solutions and more highly brominated PBDEs had a stronger uptake capability. PBDEs were detected in the stems and leaves of maize after exposure but rarely detected in the blank control plants. Furthermore, PBDE concentrations decreased from roots to stems and then to leaves, and a very clear decreasing gradient was found in segments upwards along the stem. These altogether provide substantiating evidence for the acropetal translocation of PBDEs in maize. More highly brominated PBDEs were translocated with more difficulty. Radial translocation of PBDEs from nodes to sheath inside maize was also observed. Both acropetal and radial translocations were enhanced at higher transpiration rates, suggesting that PBDE transport was probably driven by the transpiration stream. Debromination of PBDEs occurred in all parts of the maize, and debromination patterns of different parent PBDEs and in different parts of a plant were similar but with some differences. This study for the first time provides direct evidence for the acropetal translocation of PBDEs within plants, elucidates the process of PBDE transport and clarifies the debromination products of PBDEs in maize.

Enhanced debromination of 4-bromophenol by the UV/sulfite process：Efficiency and mechanism

Halogenated aromatic compounds have attracted increasing concerns due to their toxicity and persistency in the environment, and dehalogenation is one of the promising treatment and detoxification methods. Herein, we systematically studied the debromination efficiency and mechanism of para-bromophenol（4-BP） by a recently developed UV/sulfite process. 4-BP underwent rapid degradation with the kinetics accelerated with the increasing sulfite concentration, pH（6.1–10） and temperature, whereas inhibited by dissolved oxygen and organic solvents. The apparent activation energy was estimated to be 27.8 kJ/mol. The degradation mechanism and pathways of 4-BP were explored by employing N2O and nitrate as the electron scavengers and liquid chromatography/mass spectrometry to identify the intermediates. 4-BP degradation proceeded via at least two pathways including direct photolysis and hydrated electron-induced debromination. The contributions of both pathways were distinguished by quantifying the quantum yields of 4-BP via direct photolysis and hydrated electron production in the system. 4-BP could be readily completely debrominated with all the substituted Br released as Br-, and the degradation pathways were also proposed. This study would shed new light on the efficient dehalogenation of brominated aromatics by using the UV/sulfite process.

Enhanced debromination of 2,2’,4,4’-tetrabromodiphenyl ether(BDE-47)by zero-valent zinc with ascorbic acid

A new technique of zero-valent zinc coupled with ascorbic acid(ZVZ/AA)was developed and applied to debrominate the 2,2,,4,4,-Tetrabromodiphenyl ether(BDE-47),which achieved high conversion and rapid debromination of BDE-47 to less-or non-toxic forms.The reaction conditions were optimized by the addition of 100 mg/L Z V Z particles and 3 mmol/L A A at original solution p H=4.00 using the solvent of methanol/H2O(v:v=4:6),which could convert approximately 94%of 5 mg/L BDE-47 into lower-brominated diphenyl ethers within a 90 min at the ZVZ/AA system.The high debromination of BDE-47 was mainly attributed to the effect of A A that inhibits the formation of Zn(Ⅱ)(hydr)oxide passivation layers and promotes the corrosion of ZVZ,which leads to increase the reactivity of ZVZ.Additionally,ion chromatography and gas chromatography mass spectrometry analyses revealed that bromine ion and lower-debromination diphenyl ethers formed during the reduction of BDE-47.Furthermore,based on the generation of the intermediates products,and its concentration changes over time,it was proposed that the dominant pathway for conversion of BDE-47 was sequential debromination and the final products were diphenyl ethers.These results suggested that the ZVZ/AA system has the potential for highly efficient debromination of BDE-47 from wastewater.

Chemical reductive technologies for the debromination of polybrominated diphenyl ethers: A review

Polybrominated diphenyl ethers(PBDEs)are widely used as brominated flame retardants,which had attracted amounts of attention due to their harmful characteristics of high toxicity,environmental persistence and potential bioaccumulation.Many chemical reductive debromination technologies have been developed for the debromination of PBDEs,including photolysis,photocatalysis,electrocatalysis,zero-valent metal reduction,chemically catalytic reduction and mechanochemical method.This review aims to provide information about the degradation thermodynamics and kinetics of PBDEs and summarize the degradation mechanisms in various systems.According to the comparative analysis,the rapid debromination to generate bromine-free products in an electron-transfer process,of which photocatalysis is a representative one,is found to be relatively difficult,because the degradation rate of PBDEs depended on the Br-rich phenyl ring with the lowest unoccupied molecular orbital(LUMO)localization.On the contrary,the complete debromination occurs easily in other systems with active hydrogen atoms as the main reactive species,such as chemically catalytic reduction systems.The review provides the knowledge on the chemical reductive technique of PBDEs,which would greatly help not only clarify the degradation mechanism but also design the more efficient system for the rapid and deep debromination of PBDEs in the future.

A Novel Debromination of vic-Dibromides to Alkenes with InCl_3(cat.)/Sm System in Aqueous Media

A novel debromination of vic-dibromides to alkenes with InCl3(cat.)/Sm system in aqueous media has been de- veloped. The reaction gives the E-isomers with excellent yields.

Electrocatalytic debromination of BDE-47 at palladized graphene electrode

Graphene electrodes （Ti/Gr） were prepared by depositing Gr sheets on Ti substrate, followed by an annealing process for enhancing the adhesion strength. Electrochemical impedance spectroscopies and X-ray dif- fraction patterns displayed that the electrochemical behavior of Ti/Gr electrodes can be improved due to the generation of TiO2 layer at Ti-Gr interface during the annealing process. The palladized Gr electrodes （Ti/Gr/Pd） were prepared by electrochemical depositing Pd nanoparticles on Gr sheets. The debromination ability of Ti/Gr/Pd electrodes was investigated using BDE-47 as a target pollutant with various bias potentials. The results indicated that the BDE-47 degradation rates on Ti/Gr/Pd electrodes increased with the negative bias potentials from 0V to -0.5 V （vs. SCE）. Almost all of the BDE-47 was removed in the debromination reaction on the Ti/Gr/Pd electrode at - 0.5 V for 3 h, and the main product was diphenyl ethers, meaning it is promising to debrominate completely using the Ti/Gr/Pd electrode. Although the debromination rate was slightly slower at -0.3 V than that under -0.5 V, the current efficiency at -0.3 V was higher, because the electrical current acted mostly on BDE-47 rather than on water.

Synthesis,characterization,and activity of a covalently anchored heterogeneous perylene diimide photocatalyst

The consecutive two‐photon photocatalytic behavior of perylene diimide(PDI)enables it to catalyze photoreduction reactions that are thermodynamically unfavorable via single‐photon processes.In this work,we developed a heterogeneous PDI photocatalyst by covalently binding PDI molecules on the surface of nanosilica.This photocatalyst structure overcomes the intrinsic limitation of the low solubility of PDI,but retains its consecutive two‐photon photocatalytic property.Detailed characterization of the photocatalyst by techniques such as thermogravimetric analysis,solid‐state nuclear magnetic resonance spectroscopy,and Fourier transform infrared spectroscopy indicated that the PDI molecules were anchored covalently on the surface of nanosilica.The obtained photocatalyst reduced aryl halides under visible‐light irradiation in polar organic solvent and in water.The present study provides a promising strategy to realize two‐photon activity of PDI in common solvents for photocatalytic applications.

Density Functional Theory Study of Marine Polybrominated Diphenyl Ethers in Anaerobic Degradation

Polybrominated diphenyl ethers(PBDEs)are a kind of serious pollutants in the ocean.Biodegradation is considered as an economical and safe way for PBDEs removal and reductive debromination dominates the initial pathway of anaerobic degradation.On the basis of experimental study,Octa-BDE 197,Hepta-BDE 183,Hexa-BDE 153,Penta-BDE 99 and Tetra-BDE 47 were selected as the initial degradation objects,and their debromination degradation were studied using density functional theory.The structures were optimized by Gaussian 09 program.Furthermore,the molecular orbitals and charge distribution were analyzed.All C-Br bond dissociation energies at different positions including ortho,meta and para bromine atoms were calculated and the sequence of debromination was obtained.There is a close relationship between molecular structure,charge,molecular orbital and C-Br bond.All PBDEs exhibited similar debromination pathways with preferential removal of meta and para bromines.

Fuel Oil Production from Two-Stage Pyrolysis-Catalytic Reforming of Brominated High Impact Polystyrene Using Zeolite and Iron Oxide Loaded Zeolite Catalysts

The experiments of two-stage pyrolysis and catalytic reforming of high impact polystyrene (HIPS) containing brominated flame retardants and antimony trioxide (Sb2O3) were conducted in the presence of four zeolite catalysts in order to remove the bromine content from the derived oil products. The four catalysts used were natural zeolite (NZ), iron oxide loaded natural zeolite (Fe-NZ), HY zeolite (YZ) and iron oxide loaded HY zeolite (Fe-NZ). The effect of catalyst types on the product yield, the gas and oil product composition and the debromination efficiency of the oil products was evaluated in details. The results showed that the loading of iron oxides reduced the pore size and surface areas of natural zeolite and HY zeolite. Regardless of the presence of catalysts, the single-ring aromatic compounds were the main components of the oil products, such as ethylbenzene, toluene, styrene and cumene. Meanwhile, when YZ and Fe-YZ were used, the two-ring and multi-ring aromatic compounds in the oils, as well as the yield of gas products, significantly increased at the expense of valuable single-ring aromatic compounds. Furthermore, in terms of the debromination performance of the oil products, Fe-NZ and Fe-YZ were better than NZ and YZ, duo to the loading of iron oxide, which could react with derived HBr and then remove more bromine from the oil products.

A Facile and Highly Stereosclective Reductive Dcbromination of AnhydrO-6- (R)-Hydroxyethyl- 6-Bromopenicillin

Reductive debromination of anhydro-6-(R)-hydroxycthyl-6-(R) 7 by zinc in ammonium acetate gave 9 in 81% yield with high stcreosclectivity of 6-(α):6-(β)= 13: 1

Effective remediation of organic-metal co-contaminated soil by enhanced electrokinetic-bioremediation process

This work investigates the influence of electrokinetic-bioremediation(EK-BIO)on remediating soil polluted by persistent organic pollutants(POPs)and heavy metals(mainly Cu,Pb and Ni),originated from electronic waste recycling activity.The results demonstrate that most of POPs and metals were removed from the soil.More than 60%of metals and 90%of POPs in the soil were removed after a 30-day EK-BIO remediation assisted by citrate.A citrate sodium concentration of 0.02 g/L was deemed to be suitable because higher citrate did not significantly improve treatment performance whereas increasing dosage consumption.Citrate increased soil electrical current and electroosmotic flow.After remediation,metal residues mainly existed in stable and low-toxic states,which could effectively lower the potential hazard of toxic metals to the surrounding environment and organisms.EK-BIO treatment influenced soil microbial counts,dehydrogenase activity and community structure.

Seasonal variations of polybrominated flame retardants bound to car dust under Mediterranean climate

Polybrominated diphenyl ethers（PBDEs） are commercial flame retardants that have been commonly used in vehicle interior to reduce fire-related hazards. Due to high temperatures and intense insolation that can be attained inside cars parked in the sun, additive PBDEs are prone to leach out and attach to in-vehicle dust, as well as to photo-debrominate. This study examines seasonal variations of concentrations of three common PBDE congeners（BDE-47, BDE-99 and BDE-209） in car dust in Israel. The overall concentrations of these BDEs ranged from 1 to 29 μg/g, and were higher in the summer than in the winter（average of 10.2 and5.3 μg/g, respectively）. Congener-specific concentrations showed distinct seasonal pattern,representing the interplay between leaching, evaporation and photodebromination. Photolysis of the three congeners, while adsorbed on glass filters and exposed to solar radiation, revealed first order kinetics with debromination rates on the order of 10-2/min. Hence, seasonal variations of the meteorological conditions were found to affect the in-vehicle PBDE concentrations, and are therefore expected also to affect the exposure of passengers to PBDEs.

Removal of decabromodiphenyl ether （BDE-209） by sepiolite-supported nanoscale zerovalent iron

Nanoscale zerovalent iron （nZVI） synthesized using sepiolite as a supporter was used to investigate the removal kinetics and mechanisms of decabromodiphenyl ether （BDE-209）. BDE-209 was rapidly removed by the prepared sepiolite-supported nZVI with a reaction rate that was 5 times greater than that of the conventionally prepared nZVI because of its high surface area and reactivity. The degradation of BDE-209 occurred in a stepwise debromination manner, which followed pseudo- first-order kinetics. The removal efficiency of BDE-209 increased with increasing dosage of sepiolite-supported nZVI particles and decreasing pH, and the efficiency decreased with increasing initial BDE-209 concentrations. The presence of tetrahydrofuran （THF） as a cosolvent at certain volume fractions in water influenced the degrada- tion rate of sepiolite-supported nZVI. Debromination pathways of BDE-209 with sepiolite-supported nZVI were proposed based on the identified reaction intermedi- ates, which ranged from nona- to mono-brominated diphenylethers （BDEs） under acidic conditions and nonato penta-BDEs under alkaline conditions. Adsorption on sepiolite-supported nZVI particles also played a role in the removal of BDE-209. Our findings indicate that the particles have potential applications in removing environ- mental pollutants, such as halogenated organic contami- nants.

Vapor-solid interfacial reaction and polymerization for wafer-scale uniform and ultrathin two-dimensional organic films

Chemical vapor deposition is a conventional synthesis method for growing large-scale and high-quality two-dimensional materials,such as graphene,hexagonal boron nitride,and transition-metal dichalcogenides.For organic films,solution-based methods,such as inkjet printing,spin coating,and drop and micro-contact printing,are commonly used.Herein,we demonstrate a general method for growing wafer-scale continuous,uniform,and ultrathin(2-5 nm)organic films.This method is based on a copper(Cu)surfacemediated reaction and polymerization of several equivalent bromine(Br)-containingπ-conjugated small molecules(C_(12)S_(3)Br_(6),C_(24)H_(4)O_(2)Br_(2),and C_(24)H_(12)Br_(2)N_(4)),in which local surface-mediated polymerization and internalπ-πinteractions among organic molecules are responsible for the dimension and uniformity control of the thin films.Specifically,the growth rate and morphology of thin films were found to be Cu-facet-dependent,and single-crystal Cu(111)surfaces could improve the uniformity of thin films.In addition,the number of Br groups and size of organic molecules were critical for crystallinity and thin-film formation.This method can be used to fabricate heterostructures,such as organic film/graphene,giving room for various functional materials and device applications.