Catalytic Debromination Research Articles

Quantum chemical study on the catalytic debromination mechanism of brominated epoxy resins

The study employed Density Functional Theory (DFT) to investigate the catalytic debromination mechanism of brominated epoxy resins (BERs) by iron (Fe) and copper (Cu) catalysts. By introducing electric field (EF), intramolecular electron transfer and polarization effects on BERs debromination were explored and experimentally validated. Results indicated that the bond dissociation energy (BDE) of the C-Br bond was 312.27 kJ/mol without catalysis, while with Fe, Cu, and EF, it was 114.47 kJ/mol, 94.85 kJ/mol, and 292.59 kJ/mol, respectively, enhancing reactivity. EF parallel to the C-Br bond and oriented toward the C atom, altered electrostatic potential and dipole moment around C-Br bond, leading to 68.60% and 50.19% increment in electronic contribution difference and molecule polarity, respectively, thereby reducing the C-Br BDE. Fe and Cu facilitated electron transfers with BERs, inducing reactions between their negative electrostatic potentials and Br's positive potential, changing electron sharing, resulting in 19.87% and 12.11% increase in polarity, respectively, and further BDE reduction. Structural modifications by the EF and catalysts also intensified van der Waals forces with bromine atoms and decreased spatial hindrance, collectively making C-Br bond breakage easier. Experiments revealed the EF enhanced BERs' debromination efficiency but hindered Fe/Cu's catalysis at lower temperatures.

Enhanced bromine fixation and tar lightweighting in co-pyrolysis of non-metallic fractions of waste printed circuit boards with Bayer red mud

A co-pyrolysis process for non-metallic fractions (NMFs) from WPCBs with Bayer red mud (RM) is proposed to upgrade pyrolysis products in this study. High bromine fixation efficiency was realized, and higher content of lightweight pyrolysis tar was obtained. The mechanism of catalytic pyrolysis and simultaneous bromine fixation of NMFs by RM was investigated by experiments and theoretical calculations. The three inorganic components of Fe2O3, CaCO3 and Al2O3 in RM played key roles in the catalytic pyrolysis of NMFs, and their order of catalytic debromination effect was CaCO3 > Fe2O3 > Al2O3. By adding 15 wt% RM, the pyrolysis solid residue could fix 89.55 wt% bromine, compared with 35.42 wt% of NMFs without adding RM, due to the formation of FeBr2 and CaBr2 from Fe2O3 and CaCO3 in RM, respectively. Tar lightweighting was realized by reducing the energy barrier of the direct decomposition of tetrabromobisphenol A (TBBPA) in NMFs. The order of effect of the three key components on the tar lightweighting was Fe2O3 > Al2O3 > CaCO3. The content of lightweight tar in the tar obtained by catalytic pyrolysis of NMFs with 15 wt% RM was 44.29% higher than that in the tar obtained by direct pyrolysis of NMFs. This work provides a theoretical guidance for the low-cost and eco-friendly recycling of e-wastes by co-pyrolysis with RM.

Catalytic debromination of waste brominated resin by co-pyrolysis with Pd-containing spent automotive catalysts

A "treating the wastes with wastes" approach was provided in this study, where spent automotive catalysts were added into waste brominated resin for debromination by co-pyrolysis. Spent automotive catalyst in this study was the Pd-only ternary automotive catalyst and the content of Pd was 493.89 μmol/kg. The proportions of Pd(0) and Pd(Ⅱ) in spent automotive catalyst were 86.37% and 13.63%, respectively. Wrapped Pd invalidated the catalytic effect of automotive catalyst. The debromination rate of brominated resin could be increased from 12.73% to 66.86% after co-pyrolysis with spent automotive catalyst powder at 260°C. The catalytic debromination of Pd on brominated resin relied on the oxidative addition and decomposition reactions. Aryl bromides in 2,2′,4,4′-tetrabromodiphenyl ether would be attacked by Pd in turn according to the higher positive charge. This work contributes scientific information and approach to the reuse of spent automotive catalysts and the safe disposal of brominated resin together.

Highly efficient catalytic debromination of tetrabromodiphenyl ether with hydrazine as reducing agent: The role of the interaction between the catalyst and the reducing agent

It is still urgently needed to clarify how the reductive dehalogenation is accelerated by the interaction between the catalyst and the reducing agent. In the present work, both Pd and Cu were observed to induce the debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) with hydrazine hydrate (N2H4·H2O) as reducing agent. In the case of Pd system, all the added BDE47 was debrominated to bromine-free products within 20 min. However, much different debromination behaviors of BDE47 were observed when Cu was used as the catalyst: in the initial stage the debromination efficiency of BDE47 could reach up to 55.3% within 0.5 min; nevertheless the complete debromination could not be achieved by prolonging reaction time. With the aid of DFT calculations, the above-mentioned great differences were attributed to the affinity of Pd to both H and N atoms, and strong Cu–N coordination existed between Cu and the adsorbed hydrazine molecules. The dissociation energy for the cleavage of N–H and N-N bonds of N2H4·H2O adsorbed on Cu was very low, and hence the debromination of BDE47 was ultra-fast due to the spontaneously cleavage of N–H bond but it was inhibited at the later stage by the generated ammonium species (poisoning effect to the Cu catalyst) due to N-N bond cleavage. In contrast, the dissociation energy for the cleavage of N–H bond on the surface of Pd was higher and no ammonium was detected. These guarantee the continuously fast and complete debromination of BDE47 and its intermediates. These new insights to the catalytic mechanism through the interaction between the catalyst and the reducing agent will help to construct an efficient system to remove halogenated organic pollutants.

Synthesis, characterization, and debromination reactivity of cellulose-stabilized Pd/Fe nanoparticles for 2,2',4,4'-tretrabromodiphenyl ether.

In this study, two kinds of cellulose derivatives (polyanionic cellulose (PAC) and hydroxypropylmethyl cellulose (HPMC)) were selected as stabilizers of Pd/Fe nanoparticles (NPs) to investigate their influences on the debromination performances of 2,2',4,4'-tretrabromodiphenyl ether (BDE47). Field emission scanning electron microscope (FE-SEM) images revealed that the cellulose-stabilized Pd/Fe NPs were smaller and more uniform than the bare-Pd/Fe NPs. X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS) results suggested that cellulose coatings found on Pd/Fe NPs surfaces featured some antioxidation abilities, which followed the order of HPMC < PAC. Sedimentation tests demonstrated that the stabilizing power of PAC for Pd/Fe NPs was higher than that of HPMC. Fourier transfer infrared spectrometer (FTIR) results indicated that PAC molecules were bound to the Pd/Fe NPs surfaces by polar covalent bonds and hydrogen bonds, while HPMC molecules interacted with the nanoparticles by hydrogen bonds. Batch debromination test for BDE47 demonstrated that the catalytic debromination rate with cellulose-stabilized Pd/Fe NPs was higher than that with bare-Pd/Fe NPs during reaction period of 15 min. Overall, this study indicated that both celluloses are beneficial to forming smaller, more regular, stable and antioxidative Pd/Fe NPs, leading to higher debromination reactivity for BDE47 compared with the bare-Pd/Fe NPs. Therefore Pd/Fe NPs can be utilized as a promising remediation technology for the contaminated groundwater and soils.

Debromination of 1,2,4,5-Tetrabrominated Benzene in Alcohol Solution with Nanoscale Pd/C Particles: Factors, Pathways, and Mechanism

In this study, the catalytic debromination of 1,2,4,5-tetrabrominated benzene (1245TBB) was performed in a solution of NaOH in alcohol (Visopropanol:Vmethanol = 99:1) in the presence of a nanoscale catalyst Pd/C at a temperature of 50°C. The final degradation product of 1,2,4,5-tetrabrominated benzene is benzene. The debromination efficiency of 1245TBB and its degraded intermediate products (1,2,4-tribromobenzene, 1,2,-dibromobenzene, and bromobenzene) were highly dependent on the Pd/C loading and NaOH concentration. The catalyst life was evaluated, which showed that the deactivated catalyst could be reactivated about 30% after washing with 100 mmol L-1 NaOH solution in isopropanol. The possible 1245TBB debromination mechanism and pathways are also proposed and discussed in this study.

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.

Complete catalytic debromination of polybrominated diphenyl ethers over a silica-supported palladium nanoparticle catalyst

Polybrominated diphenyl ethers (PBDE) are widely used as brominated flame retardants, and the release of PBDE into the environment is of great concern. Here, the catalytic debromination of PBDE was achieved with a silica-supported Pd nanoparticle catalyst in a solution of 2-propanol/methanol 99/1 v/v containing dissolved NaOH. Results show that decabromodiphenyl ether (deca-BDE) was completely debrominated at 45 °C into two bromine-free products, diphenyl ether (55 %) and dibenzofuran (45 %), according to gas chromatography–mass spectrometry analysis. This finding indicates that the catalytic reaction included not only substitution of a bromine atom by a hydrogen atom but also a cyclization arising from a C–C bond formation at the ortho positions of the diphenyl ether moiety. Results further show that 2,2′,4,4′-tetrabromodiphenyl ether, having two bromines in ortho positions, was converted to diphenyl ether (90 %) and dibenzofuran (10 %). 4,4′-Dibromodiphenyl ether, having no ortho bromines, yielded only diphenyl ether. This study is the first showing the complete catalytic debromination of deca-BDE to bromine-free products under mild conditions.

Photochemical dehalogenation mediated by macrocyclic nickel(II) complexes

A new photochemical dehalogenation system mediated by macrocyclic nickel(II) complexes was developed. Using this system, which consists of a macrocyclic nickel(II) complex catalyst, triethanolamine (TEOA) as a sacrificial reductant, and the ruthenium complex [Ru(bpy)3](ClO4)2 as a photosensitizer, catalytic debromination of 1-bromo-4-t-butylbenzene in acetonitrile was effectively carried out. The catalytic capabilities of various macrocyclic nickel(II) complexes in debromination reactions were also elucidated.

Effect of poly(ethylene terephthalate) on the pyrolysis of brominated flame retardant containing high impact polystyrene and catalytic debromination of the liquid products

The pyrolysis of brominated flame retardant containing high impact polystyrene (HIPS-Br) mixed with poly(ethylene terephthalate) (PET) was performed at 430 °C under atmospheric pressure by a batch operation. The addition of PET to HIPS-Br affected significantly the formation of decomposition products and the degradation behavior of HIPS-Br. We have found the following observations on the addition of PET during the pyrolysis of HIPS-Br: (i) the rate of formation and the yield of liquid products decreased, (ii) the residue and gaseous products formation increased, (iii) the average carbon number (Cnp) of liquid products reduced from 12.5 to 9.1, (iv) the yield of high molecular weight hydrocarbons (C 16–C 20) decreased and the amount of hydrocarbons from C 6 to C 10 doubled, (v) heavy waxy compounds were formed on the top of the glass reactor wall in addition to the solid residue on the bottom of the reactor, (vi) antimony compounds were observed in the solid residue, as opposed to the formation of antimony tribromide (SbBr 3) detected in the liquid products of HIPS-Br in the absence of PET. We attempted the debromination of brominated liquid hydrocarbons using iron and calcium based carbon composites for the production of halogen free liquid hydrocarbons, which can be used as a feedstock in a refinery or as a fuel.

Effect of Sb2O3 in brominated heating impact polystyrene (HIPS-Br) on thermal degradation and debromination by iron oxide carbon composite catalyst (Fe-C)

The iron oxide carbon composite catalyst (Fe-C) was prepared and used for catalytic debromination process during pyrolysis of heating impact polystyrene (HIPS-Br) with various brominated flame retardants at 430°C into fuel oil. The effect of antimony oxide (Sb2O3: synergist) in HIPS-Br containing decabromo diphenyl oxide (DDO) and decabromo diphenyl ethane (DDE) as flame retardant was investigated. The thermal degradation of HIPS-Br produced various brominated hydrocarbons and also hydrobromic acid (HBr) in addition to various hydrocarbons. The synergist (Sb2O3) reacted with the hydrogen bromide evolved during the pyrolysis process and formed the SbBr3 in the liquid products. The presence of bromine content (organic and inorganic) in liquid products is not desirable to use as a fuel oil. The use of iron oxide carbon composite catalyst (Fe-C) during pyrolysis debrominated (ca. 99%) the bromine compounds from liquid products. The presence of Sb2O3 (5wt.%) decreased both the hydrogen bromide and brominated hydrocarbons by forming SbBr3 and produced high quantity of lower hydrocarbons (C7C11). Thermogravimetric analysis (TGA) revealed that the presence of Sb2O3 in HIPS-Br decreased the degradation temperature. Powder X-ray diffraction results showed the presence of Fe3O4 phase in fresh Fe-C. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) shows the presence of Sb and Br in used Fe-C catalyst in the degradation process.

Thermal degradation of ABS-Br mixed with PP and catalytic debromination by iron oxide carbon composite catalyst (Fe–C)

The degradation of brominated (Br: 9.59 wt%) flame retardant containing acrylonitrile–butadiene–styrene (ABS) copolymer [waste from electric and electronic equipment, (WEEE)] mixed with polypropylene (PP) was performed at 450 °C using iron oxide carbon composite catalyst (Fe–C) and produced bromine-free liquid products. The majority of nitrogen present in the acrylonitrile portion of ABS-Br was converted into ammonia and also light aliphatic nitriles. The liquid products can be used as a fuel oil or feedstock in the petroleum refinery.

Nickel(II) meso-Tetraphenyl-Homoporphyrins, -secochlorins, and -chlorophin: Control of Redox Chemistry by Macrocycle Rigidity

This paper presents the first electrochemical study of Ni(II) secochlorins, chlorophin, and homoporphyrins and demonstrates the influence of macrocycle-rigidity on the site of electroreduction. Oxidations and reductions were investigated by cyclic voltammetry. The measured electrode potentials were found to be dependent on the nature of the substituents attached to the porphyrinic moiety and on the ring flexiblitiy. The voltammetric behavior of these molecules when employed as catalysts for the electrochemical catalytic debromination of trans-1,2-dibromocyclohexane was used to determine whether reduction peaks were due to a metal-based (formation of catalytically active Ni(I) complexes) or ligand-based (formation of catalytically less active π-anion radical) reduction. The results showed that the homoporphyrins formed ligand-based reduction products. The homoporphyrins are locked into a nonplanar conformation stabilizing the small Ni(II) ion which results in their inability to accommodate the larger Ni(I)...

Synthesis of the deuterated compounds diethyl-4-D-pyridine-2,6-dicarboxylate and diethyl-3,4,5-D3-pyridine-2,6-dicarboxylate by catalytic reductive debromination

The synthesis of the mono- and trideutero compounds diethyl-4-D-pyridine-2,6-dicarboxylate (4) and diethyl-3,4,5-D3-pyridine-2,6-dicarboxylate (5) was achieved under a deuterium gas atmosphere by reductive debromination of diethyl-4-bromopyridine-2,6-dicarboxylate (1) and diethyl-3,4,5-tribromopyridine-2,6-dicarboxylate (2), respectively, using palladium black as catalyst and dichloromethane as solvent. The deuterium incorporation at the specified positions exceeded 95%. © 1998 John Wiley & Sons, Ltd.

Stereocontrolled Synthesis of (11Z)-Retinal and Its Analogues.

Suzuki coupling of stereochemically pure (Z)-bromotetraene 1-which is extremely unstable but can be kept in frozen benzene in the presence of a small amount of PPh3 at &sminus 01;20°C-and (Z)-alkenylboronic acid 2 provides the stereocontrolled synthesis of (11Z)-retinal 3. The 11Z configuration, which is introduced by selective catalytic debromination of the corresponding dibromo precursor of 1, is retained in this step. TBDMS = tBuMe2 Si.

σ-Thienyl complexes of palladium(II), trans-PdBr(C 4H 4- nBr n-1 S- C)(PPh 3) 2 ( n = 1–4), from oxidative addition of bromothiophenes to Pd(PPh 3) 4. X-ray structural identification of key intermediates of catalytic debromination of 2-bromothiophene and tetrabromothiophene

Oxidative addition reactions of Pd(PPh 3) 4 with bromothiophenes C 4H 4- n Br n S ( n = 1–4) occur readily at RT to give σ-thienyl complexes trans-PdBr(C 4H 4- n Br n-1 S- C)(PPh 3) 2 in yields ⩾ 85%. The products are intermediates in the regioselective reduction of bromothiophenes catalyzed by Pd(0). Palladation invariably occurs at the carbon adjacent to the thienyl sulfur. Single crystal X-ray crystallographic determination was carried out on PdBr(2-thienyl)(PPh 3) 2, 1, and PdBr(3,4,5-tribromo-2-thienyl)(PPh 3) 2, 6. Crystal data for 1: space group Pben, a = 19.354(1), b = 10.760(1), c = 16.451(1) A ̊ , Z = 4, 3106 reflections, R = 0.0614: for 6: space group P2 1/ n, a = 11.361(2), b = 13.049(3), c = 26.670(5)Å, β = 102.00(3)°, Z = 4, 3577 reflections, R = 0.0375. Reduction of PdBr(3,4-dibromo-2-thienyl)(PPh 3) 2, 5, by NaBH 4 gives 2,3-dibromothiophene.

ChemInform Abstract: Selective Catalytic Debromination by C60 Mono‐, Di‐, and Trianion

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Selective catalytic debromination by C60 mono-, di-, and trianion

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSelective catalytic debromination by C60 mono-, di-, and trianionYouqin Huang and Danial D. M. WaynerCite this: J. Am. Chem. Soc. 1993, 115, 1, 367–368Publication Date (Print):January 1, 1993Publication History Published online1 May 2002Published inissue 1 January 1993https://doi.org/10.1021/ja00054a065RIGHTS & PERMISSIONSArticle Views137Altmetric-Citations26LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (296 KB) Get e-Alerts Get e-Alerts

Tritium labelling of cholest‐4‐en‐3‐one by catalytic debromination of 2,2‐6B‐tribromo‐cholest‐4‐en‐3‐one

AbstractThe catalytic debromination of 2,2,6ß‐tribromo‐cholest‐4‐en‐3‐one with tritium gas (T2) yields tritium‐labelled cholest‐4‐en‐3‐one of high specific activity. The most favourable reaction parameters are reported. Using tritium‐hydrogen (TH) gas mixtures the labelling reactions are accompanied by three kinetic isotope effects the importance of which is discussed.

Catalytic Debromination of Vicinal Dibromides via Phase Transfer of Diaryltellurium Compounds

Abstract Several vicinal dibromides were debrominated to olefins by potassium disulfite in the presence of catalytic amounts of bis(4-methoxyphenyl) telluride in a two-phase system.