Bromine Source Research Articles

Smart strategy to synthesis silver‐based heterogeneous photocatalysts grown from molybdenum oxide precursor

Three silver-based photocatalysts, Ag@AgBr, Ag2Mo2O7, and Ag2MoO4-MoO3, were successfully synthesised by a smart hydrothermal strategy using molybdenum oxide as precursor in surfactant-assisted processes. The correlation among crystal structure and properties in the photocatalysts are discussed in detail. In addition to morphology control, the bromine source effect of adding surfactant cetyltrimethyl ammonium bromide in hydrothermal synthesis of plasmonic silver incorporated silver bromide photocatalyst was also found. The obtained Ag@AgBr showed higher photocatalytic activity in the degradation of methylene blue than other samples due to super sensitivity of AgBr to light and the surface plasmon resonance of Ag nanoparticles in the region of visible light.

One‐Pot Protocol for the Synthesis of Imidazoles and Quinoxalines using N‐Bromosuccinimide

AbstractN‐bromosuccinimide (NBS)‐mediated one‐pot, green, efficient and practical synthesis of substituted imidazoles and quinoxalines has been achieved by the reaction of styrenes with N‐arylbenzamidines and o‐phenylenediamines, respectively, in a water:1,4‐dioxane mixture. The reaction involves formation of an α‐bromo ketone as an intermediate in the presence of NBS and water, followed by condensation with the N‐arylbenzamidine and o‐phenylenediamine. Use of an inexpensive NBS as a bromine source as well as an oxidant, water as a solvent and readily available starting materials makes this protocol environmentally benign and economically viable. Substituted imidazoles and quinoxalines were obtained in good to excellent yields with wide functional group compatibility.magnified image

Flexible Zirconium MOFs as Bromine‐Nanocontainers for Bromination Reactions under Ambient Conditions

AbstractA series of flexible MOFs (PCN‐605, PCN‐606, and PCN‐700) are synthesized and applied to reversible bromine encapsulation and release. The chemical stability of these Zr‐MOFs ensures the framework's integrity during the bromine adsorption, while the framework's flexibility allows for structural adaptation upon bromine uptake to afford stronger host–guest interactions and therefore higher bromine adsorption capacities. The flexible MOFs act as bromine‐nanocontainers which elongate the storage time of volatile halides under ambient conditions. Furthermore, the bromine pre‐adsorbed flexible MOFs can be used as generic bromine sources for bromination reactions giving improved yields and selectivities under ambient conditions when compared with liquid bromine.

Flexible Zirconium MOFs as Bromine-Nanocontainers for Bromination Reactions under Ambient Conditions.

A series of flexible MOFs (PCN-605, PCN-606, and PCN-700) are synthesized and applied to reversible bromine encapsulation and release. The chemical stability of these Zr-MOFs ensures the framework's integrity during the bromine adsorption, while the framework's flexibility allows for structural adaptation upon bromine uptake to afford stronger host-guest interactions and therefore higher bromine adsorption capacities. The flexible MOFs act as bromine-nanocontainers which elongate the storage time of volatile halides under ambient conditions. Furthermore, the bromine pre-adsorbed flexible MOFs can be used as generic bromine sources for bromination reactions giving improved yields and selectivities under ambient conditions when compared with liquid bromine.

Fe3O4 MNPs-DETA/Benzyl-Br3: A new magnetically reusable catalyst for the oxidative coupling of thiols

GRAPHICAL ABSTRACT

Horizontal and vertical structure of reactive bromine events probed by bromine monoxide MAX-DOAS

Abstract. Heterogeneous photochemistry converts bromide (Br−) to reactive bromine species (Br atoms and bromine monoxide, BrO) that dominate Arctic springtime chemistry. This phenomenon has many impacts such as boundary-layer ozone depletion, mercury oxidation and deposition, and modification of the fate of hydrocarbon species. To study environmental controls on reactive bromine events, the BRomine, Ozone, and Mercury EXperiment (BROMEX) was carried out from early March to mid-April 2012 near Barrow (Utqiaġvik), Alaska. We measured horizontal and vertical gradients in BrO with multiple-axis differential optical absorption spectroscopy (MAX-DOAS) instrumentation at three sites, two mobile and one fixed. During the campaign, a large crack in the sea ice (an open lead) formed pushing one instrument package ∼ 250 km downwind from Barrow (Utqiaġvik). Convection associated with the open lead converted the BrO vertical structure from a surface-based event to a lofted event downwind of the lead influence. The column abundance of BrO downwind of the re-freezing lead was comparable to upwind amounts, indicating direct reactions on frost flowers or open seawater was not a major reactive bromine source. When these three sites were separated by ∼ 30 km length scales of unbroken sea ice, the BrO amount and vertical distributions were highly correlated for most of the time, indicating the horizontal length scales of BrO events were typically larger than ∼ 30 km in the absence of sea ice features. Although BrO amount and vertical distribution were similar between sites most of the time, rapid changes in BrO with edges significantly smaller than this ∼ 30 km length scale episodically transported between the sites, indicating BrO events were large but with sharp edge contrasts. BrO was often found in shallow layers that recycled reactive bromine via heterogeneous reactions on snowpack. Episodically, these surface-based events propagated aloft when aerosol extinction was higher (> 0.1 km−1); however, the presence of aerosol particles aloft was not sufficient to produce BrO aloft. Highly depleted ozone (< 1 nmol mol−1) repartitioned reactive bromine away from BrO and drove BrO events aloft in cases. This work demonstrates the interplay between atmospheric mixing and heterogeneous chemistry that affects the vertical structure and horizontal extent of reactive bromine events.

Combining Eosin Y with Selectfluor: A Regioselective Brominating System for Para-Bromination of Aniline Derivatives.

A mild, metal-free, and absolutely para-selective bromination of aniline derivatives has been developed in excellent yields, wherein the organic dye Eosin Y is employed as the bromine source in company with Selectfluor. Neither air nor moisture sensitive, this facile reaction proceeds smoothly at room temperature and completes within a short time. Mechanistic studies indicate a radical pathway; therefore, the existence of an in situ generated brominating reagent, "Selectbrom", is postulated, which may reasonably account for the unique regioselectivity for the para-bromination of N-acyl- as well as N-sulfonylanilines.

Supported C-Scorpionate Vanadium(IV) Complexes as Reusable Catalysts for Xylene Oxidation.

C-Scorpionate vanadium(IV) [VOx Cl3-x {κ3 -RC(pz)3 }] [pz=pyrazol-1-yl; x=0, R=SO3 (1); x=1, R=CH2 OH (2) or CH2 OSO2 Me (3)] complexes supported on functionalized carbon nanotubes (CNTs) are the first V-scorpionate catalysts used so far for the neat oxidation of o-, m- or p-xylene, with TBHP (70 % aqueous solution), to the corresponding toluic acids (main products), tolualdehydes and methylbenzyl alcohols. Remarkably, a p-toluic acid yield of 43 % (73 % selectivity, TON=1.34×103 ) was obtained with 2@CNT in a simple microwave-assisted mild oxidation procedure, using a very low catalyst charge (3.2×10-2 mol % vs. substrate). Further, this occurred in the absence of any bromine source, what is significant towards the development of a greener and more sustainable process for oxidation of xylenes. Moreover, reuse of catalysts with preservation of their activity was found for up to six consecutive cycles. The effects of reaction parameters, such as reaction time, temperature, amount of catalyst or type of heating source, on the performance of the above catalytic systems are reported and discussed.

Benzylic bromination catalyzed by triphenylphosphine selenide via Lewis basic activation

The synthesis of benzyl bromides was achieved under mild reaction conditions using N-bromosuccinimide as a bromine source and triphenylphosphine selenide as a catalyst. These conditions were compatible with a variety of substrates including boronic esters, protected amines to give imines, and carboxylic acids (to give phthalides when ortho to the benzylic center). A preliminary mechanistic investigation utilizing calculated bond dissociation energies (BDE) is employed to rationalize how a Lewis base can activate a radical mechanism.

In situ synthesis of tetrahedron-shaped hollow porous Ag@AgBr plasmonic photocatalysts with highly efficient visible-light performance by a template-assisted method

A one-step, facile, template-assisted synthetic route was applied to synthesize hollow porous tetrahedron-shaped Ag@AgBr plasmonic photocatalysts in situ. CuBr tetrahedrons were used as both the template and source of bromine and copper to produce AgBr and reduce Ag+ ions into metallic Ag, respectively. The novel Ag@AgBr photocatalysts could be easily obtained using this route. The valence of Ag (i.e. 0 or 1+) in the Ag@AgBr photocatalysts could be precisely controlled by the relative amount of AgNO3 to CuBr in the precursor solution. Photocatalytic performance of the Ag@AgBr plasmonic photocatalysts with different Ag to AgBr ratios was estimated by the decomposition of an organic dye (rhodamine b or RhB) and colorless phenol, under artificial simulated sunlight irradiation. When the molar ratio of AgNO3: CuBr was 1:1, the as-obtained Ag@AgBr photocatalyst (denoted as Ag@AgBr (1:1)) was capable of decoloring 98% of the RhB within 5min and the degree of mineralization was 67.1%, the best photocatalytic activity exhibited by the photocatalysts. The decomposition of phenol further confirmed the superior photocatalytic activity of Ag@AgBr (1:1) sample. The synthetic method employed in this work could enable controlled synthesis of other novel thin-shelled structures.

Decarboxylative bromination of α,β-unsaturated carboxylic acids via an anodic oxidation

A novel bromination of α,β-unsaturated carboxylic acids was developed via a decarboxylation by virtue of a direct anodic electro-oxidation. In this method, ammonium bromide was employed as a bromine source and the reaction features transition-metal-free, short time, and no additional supporting electrolyte.

Synthesis and characterization of bromine source immobilized on diethylenetriamine‐functionalized magnetic nanoparticles: A novel, versatile and highly efficient reusable catalyst for organic synthesis

Bromine source immobilized on magnetic nanoparticles functionalized with diethylenetriamine was successfully synthesized and characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometry, thermogravimetric analysis and X‐ray diffraction. The catalytic activity in the synthesis of 2,3‐dihydroquinazoline‐4(1H)‐one and polyhydroquinoline derivatives and in Knoevenagel condensation was studied. The bromine catalyst can be magnetically recovered and reused several times without significant loss of its catalytic activity. All products were obtained in high to excellent yields.

Gemini surfactant-assisted synthesis of BiOBr with superior visible light-induced photocatalytic activity towards RhB degradation

AbstractFlower-structured BiOBr photocatalyst has been synthesized successfully with Gemini surfactant as bromine source through chemical precipitation procedure. The structure, morphology and optical absorption property of the product have been characterized. The results reveal that the product is pure tetragonal phase BiOBr with band gap energy (

Free-Radical Bromotrifluoromethylation of Olefin via Single-Electron Oxidation of NaSO2CF3 by NaBrO3.

A free-radical bromotrifluoromethylation of olefin by using NaSO2CF3 and NaBrO3 has been achieved. Sodium bromate acts not only as a single-electron oxidant but also as a bromine source. A radical-clock experiment and electron-spin-resonance detection support a radical process.

Catalytic Asymmetric Bromocyclization of Polyenes.

The first catalytic asymmetric bromonium ion-induced polyene cyclization has been achieved by using a chiral BINOL-derived thiophosphoramide catalyst and 1,3-dibromo-5,5-dimethylhydantoin as an electrophilic bromine source. Bromocyclization products are obtained in high yields, with good enantiomeric ratios and high diastereoselectivity, and are abundantly found as scaffolds in natural products.

Chiral N,N'-dioxide-Sc(NTf2)3 complex-catalyzed asymmetric bromoamination of chalones with N-bromosuccinimide as both bromine and amide source.

The catalytic asymmetric bromoamination of chalcones with N-bromosuccinimide as both bromine and amide source was realized by using a chiral N,N'-dioxide-Sc(NTf2)3 complex as an efficient catalyst. The corresponding chiral bromoamination products were obtained in high yields with high dr and good ee values (up to 92% yield, 93 : 7 dr and 97% ee) under mild reaction conditions.

Oxidation of 4-bromo-4'-chlorobiphenyl, model species for forming mixed halogenated aromatic compounds

This contribution reports results from the gas-phase oxidation of 4-bromo-4'-chlorobiphenyl (4,4'-BCB) in order to fathom the formation of toxic species produced during the combustion of mixed halogenated aromatics. In their own right, mixed polybrominated/polychlorinated biphenyls (PXBs) represent a new class of environmental contaminants, recently detected in food and human tissues. Gas chromatography-quadrupole mass spectrometry (GC-QMS), gas chromatography-quadrupole time of flight mass spectrometry (GC-QTOFMS), Fourier transform infrared spectroscopy (FTIR) and ion chromatography (IC) served to analyse the volatile and semi-volatile organic compounds (V/SVOCs), including mixed halogenated dibenzo-p-dioxins and dibenzofurans (PXDD/Fs), and gaseous products including HBr/HCl. The selection of non-ortho substituted PXB as a model species yields a large number of halogenated compounds, including monochloro- and monobromobenzene and higher halogenated benzenes and naphthalenes and derivatives of halogenated benzenes (such as 1-chloro-4-ethynylbenzene). We also detect small amounts of chlorinated and mixed halogenated dibenzofurans. The present study provides insights into the formation of several classes of halogenated and mixed-halogenated pollutants in combustion processes involving both bromine and chlorine sources, such as those of brominated flame retardants and PVC plastics.

Synthesis and characterization of tribenzyl ammonium-tribromide supported on magnetic Fe3O4 nanoparticles: a robust magnetically recoverable catalyst for the oxidative coupling of thiols and oxidation of sulfides

Taking into account the principles of green chemistry, magnetic nanoparticles, especially Fe3O4 nanoparticles, open up a new chapter in modern organic synthesis to inset a fascinating, stupendous and efficient catalytic strategy for facilitating catalyst recovery in various chemical reactions. Inspired by this topic, tribenzyl ammonium-tribromide immobilized on magnetic nanoparticles (Fe3O4–TBA-Br3) as a bromine source was successfully synthesized and its catalytic activity in the oxidative coupling of thiols and oxidation of sulfides was investigated. It is the first report on the use of the immobilized bromine source on Fe3O4 nanoparticles as a nanomagnetic recyclable catalyst for the oxidative coupling of thiols. The nanosolid catalyst could be easily recovered by a simple magnetic separation and reused for several cycles without significant degradation in catalytic activity.

On the bromination of aromatics, alkenes and alkynes using alkylammonium bromide: Towards the mimic of bromoperoxidases reactivity

This article describes an efficient method of bromination of organic substrates including aromatics, alkenes and alkynes with NH4VO3 as a catalyst and H2O2 as an oxidant agent using a non-toxic and easy-to-handle source of bromine, tetrabutylammonium bromide. The process was developed under mild reaction conditions and is an innovation from reported methods in aspects such as: i) short reaction times, ii) the ability to work at room temperature, iii) regioselectivity and good yields.

ChemInform Abstract: A Metal‐Free Protocol for Aminofunctionalization of Olefins Using TsNBr2.

N,N-Dibromo-p-toluene sulfonamide (TsNBr2) has been found to be an effective reagent for various aminofunctionalization reactions. This reagent behaves both as an electrophilic bromine source as well as amine to react with olefins under different conditions to yield aminoether, imidazoline, diamine and amino bromine. The reaction proceeds rapidly under mild conditions with high regioselectivity. Olefins react with TsNBr2 in moist THF to form δ-amino ether at room temperature. Treatment of TsNBr2 with olefin in MeCN at room temperature produced imidazoline in high yield. Further modification of the reaction condition resulted in the development of a one-step procedure for the synthesis of N-acetyl,N′-tosyl diamine derivatives directly from olefin. When the olefin was treated with 2.4 mol equiv of TsNBr2 in the presence of K2CO3, N,N′-ditosyl diamine derivative was obtained in moderate yield. Instantaneous formation of aminobromine was observed when an olefin was treated with the reagent in dry CH2Cl2 at ro...