Incorporation Of Bromine Research Articles

Unexpected Incorporation of Bromine at a Non-anomeric Position during the Synthesis of an O2-Glycosylated Diazeniumdiolate

We recently reported that the novel NO-releasing O2-glycosylated diazeniumdiolates of structure 1 showed promising anti-parasitic activity against Leishmania major.1 While preparing some 2-deoxyglucose analogs for lead optimization, we have observed the facile displacement of acetate by bromide from the 4-position of peracetylated 2-deoxyglucose 2, as shown in Scheme 1, providing a convenient synthesis of 4-brominated 2,4-dideoxyglucose derivatives that would otherwise be difficult to access by currently preferred, directed synthetic routes. Scheme 1 In an effort to prepare compound 4a, peracetylated 2-deoxyglucose 2 was treated with HBr in glacial acetic acid. A tar assumed to be bromide 3 was formed and immediately reacted with diazeniumdiolate salt 5 to generate a product expected to be 4a. However, this easily crystallized, sharp-melting product was characterized by elemental analysis values that were vastly different from our expectation. Further examination revealed the presence of only two methyl singlets in the proton NMR, and mass spectrometry pointed to the presence of a bromine atom in the molecular ion isotopic cluster. Detailed analysis of the 1H NMR spectral properties showed that the halide had replaced the C4 acetoxy group with retention of configuration. Further work-up afforded 7a in 38% yield. The product 7a was deacetylated with methoxide in methanol to produce 7b. An alternate bromination procedure using BiBr3 and trimethylsilyl bromide gave 4-α-bromo-2,4-dideoxyglucosyl bromide diacetate 6, presumably the same glycosylating agent produced in the HBr/HOAc reaction. The reaction with BiBr3 was rapid, efficient, and gave a higher yield of 6 than the HBr procedure. Diazeniumdiolates generate up to two moles of NO upon hydrolysis under various conditions. Replacement of the C4 acetoxy group of compound 4b by bromine had little effect (only about three-fold) on hydrolysis rates at pH values of 14, 7.4, and 3.8–4.6 (Table 1), a key predictor of anti-leishmanial activity.1 Table 1 Half-lives of Hydrolysis at 37°C for Diazeniumdiolated Glycosides of Structure Et2NN(O)=NOR In conclusion, we have discovered a novel and simple BiBr3/TMS bromide-mediated preparation of compound 6, an extremely useful intermediate in the preparation of the 2-deoxy sugars primed for further functionality at C4. In particular, compounds 7a and 7b offer an electrophilic center at C4, making it potentially useful for further reaction with nucleophiles, including peptide chains or additional saccharides.

Differential absorbance study of effects of temperature on chlorine consumption and formation of disinfection by-products in chlorinated water

Effects of chlorine dose, reaction time and temperature on the formation of disinfection by-products (DBPs) and corresponding changes in the absorbance of natural organic matter (NOM) in chlorinated water were examined in this study. Although variations of chlorination parameters, notably those of temperature that was varied from 3 to 35 °C, influenced the kinetics of chlorine consumption and DBP release, correlations between chlorine consumption, concentrations of trihalomethanes (THMs), haloacetonitriles (HANs), other DBP species and, on the other hand, intensity of differential absorbance at 272 nm remained unaffected. THM and HAN speciation was correlated with the differential absorbance, indicating preferential incorporation of bromine at the initial phases of halogenation that correspond to low Δ A 272 values. Because the Δ A 272 parameter is a strong indicator of the formation of DBP species and chlorine decay, optimization of chlorination operations and DBPs control based on this parameter can be beneficial for many water utilities, especially those with pronounced variability of water temperature and residence times.

Bromide Oxidation and Formation of Dihaloacetic Acids in Chloraminated Water

A comprehensive reaction model was developed that incorporates the effect of bromide on monochloramine loss and formation of bromine and chlorine containing dihaloacetic acids (DHAAs) in the presence of natural organic matter (NOM). Reaction pathways accounted for the oxidation of bromide to active bromine (Br(l)) species, catalyzed monochloramine autodecomposition, NOM oxidation, and halogen incorporation into DHAAs. The reaction scheme incorporates a simplified reaction pathway describing the formation and termination of Br(l). In the absence of NOM, the model adequately predicted bromide catalyzed monochloramine autodecomposition. The Br(l) reaction rate coefficients are 4 orders of magnitude greater than HOCl for the same NOM sources under chloramination conditions. Surprisingly, the rate of NOM oxidation by Br(l) was faster than bromide catalyzed monochloramine autodecomposition by Br(l) so that the latter reactions could largely be ignored in the presence of NOM. Incorporation of bromine and chlorine into DHAAs was proportional to the amount of NOM oxidized by each halogen and modeled using simple bromine (alpha(Br)) and chlorine (alpha(Cl)) incorporation coefficients. Both coefficients were found to be independent of each other and alpha(Br) was one-half the value of alpha(Cl). This indicates that chlorine incorporates itself into DHAA precursors more effectivelythan bromine. Model predictions compared well with DHAA measurements in the presence of increasing bromide concentrations and is attributable to the increased rate of NOM oxidation, which is rate limited by the oxidation of bromide ion in chloraminated systems.

Cryptic chlorination by a non-haem iron enzyme during cyclopropyl amino acid biosynthesis

Enzymatic incorporation of chlorine, bromine or iodine atoms occurs during the biosynthesis of more than 4,000 natural products. Halogenation can have significant consequences for the bioactivity of these products so there is great interest in understanding the biological catalysts that perform these reactions. Enzymes that halogenate unactivated aliphatic groups have not previously been characterized. Here we report the activity of five proteins-CmaA, CmaB, CmaC, CmaD and CmaE-in the construction of coronamic acid (CMA; 1-amino-1-carboxy-2-ethylcyclopropane), a constituent of the phytotoxin coronatine synthesized by the phytopathogenic bacterium Pseudomonas syringae. CMA derives from l-allo-isoleucine, which is covalently attached to CmaD through the actions of CmaA, a non-ribosomal peptide synthetase module, and CmaE, an unusual acyltransferase. We show that CmaB, a member of the non-haem Fe(2+), alpha-ketoglutarate-dependent enzyme superfamily, is the first of its class to show halogenase activity, chlorinating the gamma-position of l-allo-isoleucine. Another previously undescribed enzyme, CmaC, catalyses the formation of the cyclopropyl ring from the gamma-Cl-l-allo-isoleucine product of the CmaB reaction. Together, CmaB and CmaC execute gamma-halogenation followed by intramolecular gamma-elimination, in which biological chlorination is a cryptic strategy for cyclopropyl ring formation.

Chlorination Byproduct Formation in the Presence of Humic Acid, Model Nitrogenous Organic Compounds, Ammonia, and Bromide

The formation of trihalomethanes (THMs), haloacetic acids (HAAs), and cyanogen halides (CNXs) after chlorination of synthetic solutions containing humic acid, nitrogenous organic (N-organic) compounds, ammonia, and bromide ions was studied. Humic acid (from Aldrich) was used to provide the source of the precursors. Glycine was chosen as the primary model N-organic compound and other four model N-organic compounds (including glutamic acid, glycylglycine, diethylamine, and methylamine) were also evaluated for comparison. The formation of THMs and HAAs was found to decrease with increasing glycine and ammonia concentrations but to increase with increasing bromide ion concentration. CNX formation was found to be highly sensitive to free chlorine to glycine ratios, and its formation trends were significantly affected bythe presence/absence of ammonia. The incorporation of bromine changed the byproducts speciation toward brominated species and enhanced the yields of total THMs, HAAs, and CNXs. Different model N-organic compounds exerted different effects on the formation of THMs, HAAs, and CNXs. Their effects on the formation of THMs and HAAs were likely dependent on their reactivity to chlorine in competing with the humic acid chlorination reactions. The difference in the CNCI yields was attributable to the variations in the compound structures.

Spectral investigation of alkyl polymethacrylates with halogenated carbazolyl pendant groups

Investigations of optical absorption, fluorescence and phosphorescence of alkyl methacrylates with halogenated carbazolyl pendant groups showed that incorporation of bromine and chlorine atoms into a carbazolyl group leads to an essential increase of phosphorescence yield, especially for Br. It was concluded that primarily triplet excitons exist in the polymers prepared.

Filamentous Carbon Growth on Nickel/Silica: Potassium and Bromine as Catalyst Promotors

In a previous Communication, we reported the catalytic growth of highly ordered carbon filaments during the hydrodechlorination of chlorobenzene over nickel/silica at the remarkably low temperature of 553 K. This low temperature growth was attributed to the presence of bromine and potassium on the catalyst surface, which facilitated a restructuring of the active sites leading to a destructive chemisorption of the reactant that preceded the dissolution and precipitation of carbon in an ordered fashion. In this paper, we examine the effect of bromine and potassium built into (by impregnation with KOH, HBr and KBr) a Ni/SiO2 parent sample on filamentous carbon production through ethylene decomposition. The parent catalyst delivered a low yield of carbon (0.2 g(C)g(cat)(-1)) and promoted the competing hydrogenation (to ethane) step to the same degree; hydrogenolysis to methane represented the only other significant reaction. The nature of the carbon deposition has been characterised by high-resolution transmission electron microscopy (HRTEM) and temperature-programmed oxidation (TPO). Impregnation with KOH resulted in little change in carbon yield but the hydrogenolysis step was completely suppressed. A combination of CO chemisorption/temperature programmed desorption has been employed to probe the electronic structure of the nickel sites where the presence of potassium limited CO uptake in contrast to surface bromine which served, through electron withdrawal, to strengthen the CO-Ni interaction. Incorporation of bromine into the catalyst resulted in a marked increase in nickel particle size and a dramatic enhancement of carbon yield; the sample treated with KBr delivered the appreciably higher carbon yield of 7.6 g(C)g(cat)(-1)). While the presence of bromine on the surface served to enhance carbon deposition, the additional incorporation of potassium raised the degree of order in the carbon growth.

In situ etching with AsBr3 and regrowth in molecular beam epitaxy

We report in situ etching in III-V molecular beam epitaxy (MBE) with AsBr3 as the etching species and MBE regrowth of in situ structured GaAs substrates. The application of AsBr3 provides atomic layer precise etching as well as full compatibility with MBE growth. The quality of etched interfaces in GaAs/AlGaAs heterostructures is investigated by photoluminescence (PL) and Hall-effect measurements. They indicate a slightly enhanced interface roughness for etched samples compared to as-grown structures but no incorporation of bromine could be detected. However, an insufficient removal of dopants as well as carbon and oxygen surface contamination was observed in SIMS studies. A material selectivity between the metallic components In, Ga and Al was investigated as well as a crystallographic selectivity in GaAs. Selective etching of SiO2 masked GaAs(100) substrates allows in situ preparation of extremely sharp V-grooves with almost perfectly planar {110} side facets. By MBE regrowth of V-grooves we prepared buried layers and completely embedded wires which were characterized by SEM and PL.

Spray coating device

Hydrogenated amorphous carbon (a-C:H) thin films were prepared by hydrogen plasma-enhanced atomic layer deposition (PE-ALD). The a-C:H thin films were grown at low temperatures in the range of 150–350 °C using CBr4 as the precursor and hydrogen plasma as the reactant. Raman spectroscopy, secondary ion mass spectrometry, X-ray photoelectron spectroscopy and Fourier transform infrared measurements showed that the a-C:H films consist of hydrogenated nanocrystalline sp3 diamond, disordered sp3 carbon and sp2-hybridized graphitic carbon incorporated with oxygen as a main contaminant. Moreover, the incorporation of bromine and oxygen in the a-C:H films was significantly reduced upon increasing the growth temperature from 200 to 300 °C. Surface hydroxylation and precursor exposure pretreatments were employed to saturate the adsorption of CBr4 precursors and enhance the initial nucleation of carbon during the deposition of the a-C:H thin film by the PE-ALD process. In addition, the conformal growth of a-C:H thin films on three-dimensional structures was confirmed.

Light resistance of bromine-containing polyphenylene-oxadiazole fibres

It was shown that incorporation of bromine in the aromatic rings of POD increases the light resistance of fibres. The effect of increasing the light resistance of bromine-containing POD fibres is due to quenching of the photoexcited triplet state of the polymer macromolecules by bromine.

Characteristics of donor-acceptor complexes formed in porphyrin-polymer systems and their photoactivation in electron transfer photoreaction

Donor-acceptor complexes formed between meso-tetra( p-aminophenyl)porphine moieties covalently bound to polymers (e.g. poly(methacrylic acid) (PMA) and the influence of substances with electron-accepting affinities (molecular bromine, hydrogen ions and benzylviologen) on the properties of these complexes were investigated using fluorescence and absorption spectroscopy. Electron transfer to the viologen in a system including a sacrificial electron donor (triethylamine) with accumulation of reduced benzylviologen under steady-state illumination was also studied. A correlation between IR emission assigned to charge transfer complex fluorescence and efficiency of electron transfer to the viologen has been revealed. The IR emission is the most intense in porphyrin covalently bound to PMA compared with other polymers. Differential absorption spectra of associated meso-tetra( p-aminophenyl)porphine bound to macromolecules indicate the involvement of macromolecule carboxyl groups in the structure of the donor-acceptor complex. Incorporation of molecular bromine or hydrogen ions in this structure due to non-valent interactions leads to a considerable change in the absorption spectrum of the complex. In the case of benzylviologen incorporation, its involvement in the complex structure occurs during the photoinduced electron transfer to benzylviologen in the system including the sacrificial electron donor. The appearance of unusual features in the latter system is interpreted as the photoactivation of the donor-acceptor complex.

Synthesis and thermal characterization of chemically modified phenolic resins

AbstractPhenolic resins with improved/altered thermal stability and flame retardancy were prepared by introducing flame retardant elements such as phosphorus and bromine at the monomer stage, followed by condensation with formaldehyde or hexamethylene tetramine (HMTA). Thus, monophenyl phosphoric acid (MPPA), monophenyl phosphoric acid–formaldehyde resin (MPPAF), brominated phenol–formaldehyde resin (BrPF) and 2,4,6‐tribromophenyl‐phosphoric acid–formaldehyde resin (BrMPPAF) were prepared and characterised. Thermal stability and flammability of these polymers were evaluated by TGA and LOI respectively and compared with those of phenol–formaldehyde resin (PF) and phosphorylated phenol–formaldehyde resin (PPF). The TGA (in air) of MPPAF showed enhanced thermal stability (char yield 66%) over that of PF (char yield 52%) and PPF (char yield 58%) indicating the role of phosphorus in imparting thermo‐oxidative resistance to PF. The enhancement is better when phosphorus is introduced at the monomer stage. The incorporation of bromine, however, brought about an unexpected reduction in the thermal stability of PF (char yield: BrPF, 2% and BrMPPAF, 26%). Both phosphorus and bromine are found to enhance the LOI values of PF (cured) from 35 to 50, 48, and 56, respectively, for MPPAF, BrPF, and BrMPAFF. A comparison of LOI values of these resins with their char yield suggests a condensed phase mechanism for phosphorus and vapor phase mechanism for bromine operating during thermal decomposition. © 1994 John Wiley & Sons, Inc.

Ab-plane optical properties of YBa2Cu3O7- delta Bry single crystals.

Room-temperature infrared- and optical-spectroscopic measurements are reported on brominated ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.2}$ single-crystal samples. Incorporation of bromine in the lattice was observed in both Auger electron and infrared-spectroscopy experiments but the exact lattice site for bromine dopant atoms remains unknown. Five of the six in-plane infrared-active ${\mathit{E}}_{\mathit{u}}$ phonon modes were observed in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.2}$${\mathrm{Br}}_{\mathit{y}}$ samples and phonon frequency softening was observed for the 591-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ phonon [Cu(2)-O(2) in-plane stretch] mode. The frequency-dependent optical conductivity \ensuremath{\sigma}(\ensuremath{\omega}) was obtained from the Kramers-Kronig transformation of the near-normal-incidence reflectance R(\ensuremath{\omega}) measurements, and the resulting \ensuremath{\sigma}(\ensuremath{\omega}) showed the presence of a mid-infrared band (centered at \ensuremath{\sim}2500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$) in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.2}$${\mathrm{Br}}_{\mathit{y}}$.

Preparation and properties of brominated poly(arylcarboxylate)s via interfacial polycondensation

AbstractThe interfacial polycondensation method has been used for the preparation of brominated poly(arylcarboxylate)s. Brominated poly(arylcarboxylate)s can be prepared easily by mixing a solution of diacid chloride in a water‐immiscible organic solvent with an aqueous alkaline solution of bisphenol in the presence of catalyst such as quaternary ammonium salts. First, in a dichloromethane‐water system using triethylbenzylammonium chloride (TEBAC) as the catalyst a series of 2,2‐bis(4‐hydroxy‐3,5‐dibromophenyl)propane (3,3′,5,5′‐tetrabromobisphenol A, TBBPA) with isophthaloyl (I) and terephthaloyl chlorides (T) has been prepared and some properties as inherent viscosity, solubility, crystallinity, and flammability have been measured. Copolymers prepared from TBBPA and mixed T/I with 33/67–67/33 molar ratios show good solubility and amorphous nature, and can be cast into transparent and tough films with limiting oxygen index of 58–59 (ANSI/ASTM D2683‐77). Second, the effects of some variables as the nature of organic phase and catalysts, concentration of reactants, and basicity of aqueous phase on the interfacial polycondensation of TBBPA with equal parts of T and I [T/I (50/50)] was investigated in some detail. Among the solvents tested dichloromethane was found to be the best solvent and quaternary ammonium salts such as TEBAC and tetra‐n‐butylammonium bromide (TBAB) were highly efficient catalysts. Poly(arylcarboxylate)s with the highest molecular weights were obtained at an acid chloride concentration of 0.2 mol/L in dichloromethane and a concentration of TBBPA of 0.1 mol/L in alkali when TEBAC was used as catalyst. A maximum of inherent viscosity was obtained at two equivalent amounts of alkali corresponding to bisphenol. Polycondensation of several combinations of T/I (50/50) with some other tetrabromobisphenols, such as 3,3′,5,5′‐tetrabromo‐4,4′‐biphenol, 3,3′,5,5′‐tetrabromobisphenol S, 3,3′,5,5′‐tetrabromo‐4,4′‐thiodiphenol, and 3,3′,5,5′‐tetrabromophenolphthalein, were carried out with limited success. Whereas, a more favorable result could be obtained by the mixed copolycondensation of these tetrabromobisphenols and bisphenol A (BPA) with T/I (50/50). Finally, the copoly(arylcarboxylate)s from TBBPA, BPA, T, and I were prepared and characterized. The incorporation of bromine on the polymer backbone caused a decrease of inherent viscosity, glass transition temperature, crystallinity, and thermal stability of copolyarylates, whereas it caused a great enhancement of flame retardancy.

Facile incorporation of bromine into aromatic systems under conditions of water chlorination

Facile incorporation of bromine into aromatic systems under conditions of water chlorination

Regiospecific incorporation of bromine and iodine into phenols using (trimethylsilyl)phenol derivatives

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRegiospecific incorporation of bromine and iodine into phenols using (trimethylsilyl)phenol derivativesD. S. Wilbur, W. E. Stone, and K. W. AndersonCite this: J. Org. Chem. 1983, 48, 9, 1542–1544Publication Date (Print):May 1, 1983Publication History Published online1 May 2002Published inissue 1 May 1983https://doi.org/10.1021/jo00157a035RIGHTS & PERMISSIONSArticle Views1437Altmetric-Citations36LEARN 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 (469 KB) Get e-Alerts Get e-Alerts

Incorporation of bromine into Si-SiO 2 interfaces and effects on interface state distribution

An experimental study has been made of the effects of bromine treatment of (111) silicon surfaces before thermal oxidation. A sharp peak in the Si-SiO2 interface state distribution at Ev+ 0.15 eV and an overall increase in density by as much as two orders of magnitude has been observed in m.o.s. structures with SiO2 thickness of ≈ 100 Å. In a.c. conductance against bias voltage measurements, two conductance peaks are observed rather than the customary single peak.

The influence of bromine compounds on the combustion of polyolefins I. Effects on the thermal degradation

Studies have been made of the thermal degradation at about 400 °C of some polyolefins both in the presence of gaseous hydrogen bromide, and after chemical incorporation of bromine into the polymer. It has been shown that the presence of bromine in either form accelerates the degradation of polypropylene and of an equimolar polyethylene–polypropylene copolymer, while it retards the breakdown of polyethylenes which have only a relatively small degree of branching. A given amount of halogen has a much greater effect when incorporated into the polymer than when added as gaseous hydrogen bromide. These results can be explained in terms of a mechanism involving bromine atoms as chain carriers. The different rates of thermal degradation of the polyolefins and the contrasting over-all effects of bromine compounds on these reactions appear to be consequences of the more facile abstraction of hydrogen from tertiary than from secondary C—H groups.