Showing papers on "Bromide published in 2001"
TL;DR: The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5-diformylfuran (DFF) in 57% isolated yield as mentioned in this paper.
Abstract: The alcohol group of hydroxymethylfurfural (compound 1, HMF) is preferentially oxidized by dioxygen and metal/bromide catalysts [Co/Mn/Br, Co/Mn/Zr/Br; Co/Mn=Br/(Co+Mn) = 1.0 mol/mol] to form the dialdehyde, 2,5-diformylfuran (compound 2, DFF) in 57% isolated yield. HMF can be also oxidized, via a network of identified intermediates, to the highly insoluble 2,5-furandicarboxylic acid (compound 5, FDA) in 60% yield. For comparison, benzyl alcohol gives benzaldehyde in 80% using the same catalyst system. Over-oxidation (to CO2) of HMF is much higher than that of the benzyl alcohol but can be greatly reduced by increasing catalyst concentration.
337 citations
TL;DR: Hollow microspheres with ordered mesoporous walls are synthesised under ambient conditions by a simple procedure involving dilution and neutralisation of an aqueous tetraethoxysilane/cetyltrimethylammonium bromide reaction mixture.
260 citations
TL;DR: The kinetics indicate formation of BrOOO(-) as a steady-state intermediate with an acid-assisted step to give BrOH and O(2) in acidic solutions, important in studies of annual ozone depletion in the Arctic troposphere at polar sunrise.
Abstract: Reactions of ozone with Br-, SO32-, HSO3-, I-, and NO2-, studied by stopped-flow and pulsed-accelerated-flow techniques, are first order in the concentration of O3(aq) and first order in the concentration of each anion. The rate constants increase by a factor of 5 × 106 as the nucleophilicities of the anions increase from Br- to SO32-. Ozone adducts with the nucleophiles are proposed as steady-state intermediates prior to oxygen atom transfer with release of O2. Ab initio calculations show possible structures for the intermediates. The reaction between Br- and O3 is accelerated by H+ but exhibits a kinetic saturation effect as the acidity increases. The kinetics indicate formation of BrOOO- as a steady-state intermediate with an acid-assisted step to give BrOH and O2. Temperature dependencies of the reactions of Br- and HSO3- with O3 in acidic solutions are determined from 1 to 25 °C. These kinetics are important in studies of annual ozone depletion in the Arctic troposphere at polar sunrise.
186 citations
TL;DR: In this paper, the influence of halide ions on the photocatalytic process on titanium dioxide has been investigated carefully, and it was shown that in the presence of bromide, CBrCl 3 was detected as intermediate during CCl 4 degra- dation, while in the absence of chloride, formation of CCl4 was observed in the CHCl 3 degra -dation.
Abstract: The influence of halide ions on the photocatalytic process on titanium dioxide has been investigated carefully. Chloride and bromide ions, acting as hole scavengers, generate active radical species (e.g., ·Cl and ·Br) that participate in reactions with the organic com- pounds and the transient intermediates. Chloride and bromide ions have shown to deeply inhibit the degradation rate of chloroform and tetrachloromethane and to modify both the qualitative and quantitative distribution of their intermediates formed during the degradation process. In the presence of bromide, CBrCl 3 is detected as intermediate during CCl 4 degra- dation, while in the presence of chloride, formation of CCl 4 is observed in the CHCl 3 degra- dation. Fluoride ions, differently from the other halides, cannot be oxidized by the valence hole and may be used as a diagnostic tool in mechanistic studies. The influence of fluoride on phenol has been investigated, and, by choosing appropriate experimental conditions, it was possible to evaluate the role of the different active species in the photocatalytic process.
179 citations
TL;DR: The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination and the halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory.
148 citations
TL;DR: In this article, the growth and characterization of a new nonlinear metal-organic crystal, potassium thiourea bromide (PTB), was reported by slow evaporation method.
141 citations
TL;DR: Tungstate, exchanged on a (Ni,Al) layered double hydroxide, is applied as a heterogeneous catalyst in the oxidation of bromide with H2O2 and the ensuing electrophilic bromination of olefins.
Abstract: Tungstate, exchanged on a (Ni,Al) layered double hydroxide, is applied as a heterogeneous catalyst in the oxidation of bromide with H2O2 and the ensuing electrophilic bromination of olefins. The high halogenation activity of the catalyst in essentially neutral conditions mimicks the activity of V-bromoperoxidase enzymes. In water, aromatic and aliphatic olefins are selectively converted to bromohydrins; in methanol, methoxybromides are produced. In appropriate solvent conditions, the bromohydroxylation of geminally di-, tri-, and tetrasubstituted olefins proceeds via dehydrobromination to the epoxide. Evidence for this mechanism is provided by kinetic and labeling experiments. This one-pot alternative for the two-step halohydrin epoxidation process is enabled by the mild pH conditions; bromide is effective in substoichiometric, catalytic amounts. All new catalytic procedures are characterized by a high oxidative stability of the catalyst, high productivity of the catalyst on weight basis, high W turnover ...
116 citations
TL;DR: It is concluded that at plasma concentrations of bromide and thiocyanate, hypobromous acid and oxidation products of thiOCyanate are produced by eosinophil peroxidase.
Abstract: Eosinophil peroxidase has been implicated in promoting oxidative tissue damage in a variety of inflammatory conditions, including asthma It uses H(2)O(2) to oxidize chloride, bromide and thiocyanate to their respective hypohalous acids The aim of this study was to establish which oxidants eosinophil peroxidase produces under physiological conditions By measuring rates of H(2)O(2) utilization by the enzyme at neutral pH, we determined the catalytic rate constants for bromide and thiocyanate as 248 and 223 s(-1) and the Michaelis constants as 05 and 015 mM respectively On the basis of these values thiocyanate is preferred 28-fold over bromide as a substrate for eosinophil peroxidase Eosinophil peroxidase catalysed substantive oxidation of chloride only below pH 65 We found that when eosinophil peroxidase or myeloperoxidase oxidized thiocyanate, another product besides hypothiocyanite was formed; it also converted methionine into methionine sulphoxide During the oxidation of thiocyanate, the peroxidases were present as their compound II forms Compound II did not form when GSH was included to scavenge hypothiocyanite We propose that the unidentified oxidant was derived from a radical species produced by the one-electron oxidation of hypothiocyanite We conclude that at plasma concentrations of bromide (20-120 microM) and thiocyanate (20-100 microM), hypobromous acid and oxidation products of thiocyanate are produced by eosinophil peroxidase Hypochlorous acid is likely to be produced only when substrates preferred over chloride are depleted Thiocyanate should be considered to augment peroxidase-mediated toxicity because these enzymes can convert relatively benign hypothiocyanite into a stronger oxidant
108 citations
TL;DR: The formation of benzoin (Ph-CHOH-CO-Ph) from two molecules of benzaldehyde, catalyzed by 3-benzyl-5-(2-hydroxyethyl)-4-methylthiazolium bromide in methanol buffered with Et(3)N/Et( 3)NH(+)Cl(-) has been studied.
Abstract: The formation of benzoin (Ph-CHOH-CO-Ph) from two molecules of benzaldehyde, catalyzed by 3-benzyl-5-(2-hydroxyethyl)-4-methylthiazolium bromide in methanol buffered with Et3N/Et3NH+Cl- has been studied. Initial-rate studies at various concentrations of PhCHO (0.1−1.7 M) showed that the reaction is close to being first order in PhCHO. Following the reaction in deuteriomethanol, 1H NMR spectroscopy allowed rate constants for all three kinetically significant steps to be determined. These show that all three steps are partially rate-determining. A normal deuterium kinetic isotope effect for the overall reaction (kH/kD ≈ 3.4) is observed using PhCDO, and a large inverse solvent isotope effect (kD/kH ≈ 5.9) is observed using deuteriomethanol, consistent with the kinetic scheme presented here.
105 citations
TL;DR: Strong intramolecular antiferromagnetic exchange coupling between the FeIII ion, which in the chloride complex has a high-spin (SFe = 5/2) state and in the iodide complex an intermediate-spin state, and the two π radicals leads to observed ground states, St .
Abstract: The halide ligand determines the ground state for the complexes 1. The chloride complex has a pure St =3/2 state, the iodide complex a pure St =1/2 state, and the bromide complex contains both spin-state isomers (St =3/2 and 1/2) in a 1:1 ratio. Strong intramolecular antiferromagnetic exchange coupling between the FeIII ion, which in the chloride complex has a high-spin (SFe = 5/2) state and in the iodide complex an intermediate-spin (SFe =3/2) state, and the two π radicals leads to observed ground states, St .
105 citations
TL;DR: In this paper, the authors used a linear Stern-Volmer plot to measure the degree of micellar counterion dissociation (α), and found that the α values of CTAB micelles decreased with increasing the concentrations of cationic surfactants including fluorocarbon ones.
TL;DR: In this article, the relative nucleophilicity of chloride, bromide and iodide anions in [bmim][BF4] ionic liquid has been measured by studying their reaction with methyl p-nitrobenzenesulfonate.
Abstract: The relative nucleophilicity of chloride, bromide and iodide anions in [bmim][BF4] ionic liquid has been measured by studying their reaction with methyl p-nitrobenzenesulfonate ([bmim] = 1-butyl-3-methylimidazolium cation). It has been found that iodide is the most nucleophilic halide, and that chloride and bromide have approximately equal nucleophilicities (Cl− is slightly more nucleophilic than Br−) in [bmim][BF4]. Activation energies for the reaction of chloride and bromide with methyl p-nitrobenzenesulfonate have been calculated. The relative nucleophilicity of the halides has been compared with that observed in molecular solvents and in a tetraalkylammonium tetraalkylboride ionic liquid.
TL;DR: These nanometer-size cation-radical salts are shown to act as efficient "electron sponges" toward a variety of electron donors and to be isolated in pure form using SbCl(5) as an oxidant.
TL;DR: Water-soluble Pd nanoparticles modified with covalently-attached cyclodextrin (CD) receptors were prepared by the reduction of PdCl42- in dimethylformamide solution containing perthiolated β-CD and behave as active catalysts for the hydrogenation of alkenes in aqueous media.
Abstract: Water-soluble Pd nanoparticles (diameter 3.5 ± 1.0 nm) modified with covalently-attached cyclodextrin (CD) receptors were prepared by the reduction of PdCl42- in dimethylformamide solution containing perthiolated β-CD. These Pd nanoparticles behave as active catalysts for the hydrogenation of alkenes in aqueous media. For instance, the turnover frequency for the hydrogenation of 1-butenyltrimethylammonium bromide (1) was found to be 320 (moles of 1) (moles of Pd)-1 h-1 at 25 °C and 1.0 atm of H2(g). The addition of cationic ferrocene derivatives, such as ferrocenylmethyltrimethylammonium bromide (3), to the reaction medium decreases the catalytic activity of the Pd nanoparticles. Other CD substrates, such as anionic ferrocene derivatives or neutral adamantanol, are much less effective as inhibitors of the catalytic hydrogenation process.
TL;DR: In this paper, the P5X2+ ion was introduced as the first example of the previously unknown class of phosphorus-rich binary P-X cations, and the crystal structure of [P5Br2]-[Al{OC(CF3)3}]- was detd. and mol. structure calcns.
Abstract: Insertion of the intermediately formed carbene-analogous PX24 ion (X = Br, I) into one of the P-P bonds of the P4 tetrahedron led to the P5X2+ ion - the 1st example of the previously unknown class of phosphorus-rich binary P-X cations. The crystal structure of [P5Br2]+[Al{OC(CF3)3}]- was detd. and mol. structure calcns. were performed on both the bromide and iodide analogs. [on SciFinder (R)]
TL;DR: Bromination of alkenes using a combination of potassium bromide and cerium(iv) ammonium nitrate (CAN) in a two phase system consisting of water and dichloromethane affords the corresponding dibromides in excellent yield as mentioned in this paper.
TL;DR: Room-temperature ionic liquids are used as "green" recyclable alternative to chlorinated solvents for the stereoselective halogenation of alkenes and alkynes.
TL;DR: In this paper, a conjugated polymer system with propargyl side chains and N-propargylpyridinum substituent was formed, which was shown to be completely soluble in water, methanol, dimethylformamide, and dimethyl sulfoxide, and well processable into thin homogeneous film.
Abstract: Poly-(2-ethynylpyridinum bromide) (PEPBP) having propargyl side chains was prepared by the direct polymerization of 2-ethynylpyridine and propargyl bromide under mild reaction conditions without any initiator and catalysts. The polymerization proceeded well to give PEPBP with propargyl side chains in relatively high yields. Various spectral data for the polymer structure indicated that the conjugated polymer system having N-propargylpyridinum substituent was formed. This ionic polymer was completely soluble in water, methanol, dimethylformamide, dimethyl sulfoxide, and N,N-dimethylacetamide and well processable into thin homogeneous film. The photoluminescence intensity (λmax = 760 nm) of this polymer increased as the temperature was increased. At 1 KHz and room temperature, this polymer has k′ = 2.9 and σ = 7.3 × 10−10 (S/cm). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3151–3158, 2001
TL;DR: The clouding phenomenon with sodium dodecyl sulfate (SDS) in combination with tetra-n-butylammonium bromide (Bu4NBr) is reported and an unusual CP-decreasing effect of thio compounds is observed, which is discussed in terms of direct interaction of these compounds with anionic SDS micelles.
Abstract: Here we report the clouding phenomenon with sodium dodecyl sulfate (SDS) in combination with tetra-n-butylammonium bromide (Bu4NBr). Cloud point (CP) vs [Bu4NBr] curves are constructed for various fixed [SDS], and the minimum Bu4NBr concentrations required to produce CP are determined. A relationship between [SDS] and [Bu4NBr] is established that exists down to fairly low [SDS]. The presence of aromatic hydrocarbons (added up to their solubility limits) decreases the CP of a fixed SDS−Bu4NBr system. Furthermore, an increase in hydrophobicity of the aromatic hydrocarbon decreases the CP. An unusual CP-decreasing effect of thio compounds is observed, which is discussed in terms of direct interaction of these compounds with anionic SDS micelles.
TL;DR: In this paper, aqueous micelles, composed of mixtures of these surfactants, can be polymerized to yield single-phase, stable solutions, confirmed by disappearance of characteristic vinyl signals in the 1H NMR spectra, and line broadening.
Abstract: Mixtures of polymerizable surfactants have been employed to select control over interfacial curvature and phase structure, in aqueous micelles, lyotropic mesophases, and water-in-oil microemulsions. These surfactants were 11-(methacryloyloxy)undecyltrimethylammonium bromide (A), dodecyl(11-(methacryloyloxy)undecyl)dimethylammonium bromide (B), and cetyltrimethylammonium 4-vinylbenzoate (C). The single chain A and double chain B have reactive hydrophobic chain tips, whereas the single chain C possesses a polymerizable vinyl benzoate hydrophilic counterion. Aqueous micelles, composed of mixtures of these surfactants, can be polymerized to yield single-phase, stable solutions. Polymerization was confirmed by disappearance of characteristic vinyl signals in the 1H NMR spectra, and line broadening, as would be expected in polymerized micelles. Furthermore, small-angle neutron scattering (SANS) indicates that micelle structures were broadly retained after polymerization. SANS has shown that these polymerized st...
TL;DR: The combination of water-soluble radical initiator 2,2'-azobis[2-imidazolin-2-yl)propane, water- soluble chain carrier 1-ethylpiperidine hypophosphite, and surfactant cetyltrimethylammonium bromide was found to be the most suitable condition for effective radical cyclization in water for a variety of hydrophobic substrates.
TL;DR: In this article, the use of heteropolyacids in conjunction with phase transfer catalysts in the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as the oxidising agent has been investigated.
Abstract: The use of heteropolyacids in conjunction with phase transfer catalysts in the oxidation of benzyl alcohol to benzaldehyde with hydrogen peroxide as the oxidising agent has been investigated. The effect of various parameters on the conversion of benzyl alcohol was studied including the effect of the nature of the heteropolyanion as well as the effect of the partial substitution of protons in the heteropolyacid. Surfactant-type phase transfer catalysts were found to display high catalytic activity with cetyltrimethylammonium bromide (CTMAB) being the most effective phase transfer catalyst among those examined. A suitable mechanism for this reaction has been proposed and a kinetic model has been developed in order to explain the observed experimental results.
TL;DR: Results indicate that HOBr generated by eosinophil peroxidase oxidizes uracil to 5-bromouracil, raising the possibility that halogenated nucleobases generated by Eosinphil per oxidase exert cytotoxic and mutagenic effects at eos inophil-rich sites of inflammation.
Abstract: Eosinophils use eosinophil peroxidase, hydrogen peroxide (H2O2), and bromide ion (Br-) to generate hypobromous acid (HOBr), a brominating intermediate. This potent oxidant may play a role in host defenses against invading parasites and eosinophil-mediated tissue damage. In this study, we explore the possibility that HOBr generated by eosinophil peroxidase might oxidize nucleic acids. When we exposed uracil, uridine, or deoxyuridine to reagent HOBr, each reaction mixture yielded a single major oxidation product that comigrated on reversed-phase HPLC with the corresponding authentic brominated pyrimidine. The eosinophil peroxidase-H2O2-Br- system also converted uracil into a single major oxidation product, and the yield was near-quantitative. Mass spectrometry, HPLC, UV−visible spectroscopy, and NMR spectroscopy identified the product as 5-bromouracil. Eosinophil peroxidase required H2O2 and Br- to produce 5-bromouracil, implicating HOBr as an intermediate in the reaction. Primary and secondary bromamines a...
TL;DR: The cosurfactant of the microemulsion was found to be the most important factor affecting the selectivity, and alteration between 6.6% of 1‐propanol, 1‐butanol, tetrahydrofuran, and 2‐ethoxyethanol caused several substantial changes in the migration order.
Abstract: The selectivity of microemulsion electrokinetic chromatography (MEEKC) was studied utilizing some uncharged model compounds like aromatic amides, steroids, and esters of nicotinic acid. The cosurfactant of the microemulsion was found to be the most important factor affecting the selectivity, and alteration between 6.6% of 1-propanol, 1-butanol, tetrahydrofuran, and 2-ethoxyethanol caused several substantial changes in the migration order. In addition, the nature of the surfactant was found to significantly affect the selectivity. In this case, changes in order of migration was observed by replacement of half the content of sodium dodecyl sulfate (SDS) with either sodium dioctyl sulfosuccinate (SDOSS), 3-(N,N-dimethylmyristylammonio) propanesulfonate (MAPS), polyoxyethylene sorbitan monolaurate (Tween 21), and polyoxyethylene 23 lauryl ether (Brij 35). MEEKC was also accomplished with 3.3% of the anionic surfactant sodium cholate and with the cationic surfactant N-cetyl-N,N,N-trimethylammonium bromide (CTMA). Both provided substantial differences in selectivity as compared to the SDS-based systems. With SDS as surfacant, the concentration was varied within 1.0-4.5%. Minor selectivity changes were observed as the concentration of the surfacant was reduced, but the major effect was a reduction in the total migration time. The organic solvent of the microemulsion droplets was found only to have minor impact on the selectivity.
TL;DR: Reaction of sulfonimines having proximal chelating groups with crotyl bromide and indium in aqueous media gave alpha-crotylation products stereoselectively with syn-selectivity.
Abstract: Reaction of sulfonimines having proximal chelating groups with crotyl bromide and indium in aqueous media gave alpha-crotylation products stereoselectively with syn-selectivity.
TL;DR: In this article, both acetonyltriphenylphosphonium bromide (ATPB) and poly-p-styryldiphenylacetonylphosphonic bromides (A) were used as catalysts in the protection of alcohols as THP, THF, and EE ethers.
TL;DR: In this paper, Triton X-100 (TX-100) molecules coaggregate with cetyl trimethylammonium bromide (CTAB) molecules in aqueous solutions.
Abstract: 1H NMR chemical shift, spin−lattice relaxation time, spin−spin relaxation time, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements show that Triton X-100 (TX-100) molecules coaggregate with cetyl trimethylammonium bromide (CTAB) molecules in aqueous solutions. The concentration of TX-100 in the mixed solutions of this study is 3 mM, with varying molar ratios of CTAB/TX-100 (C/T) ranging from 0.5 to 2.9. The results give information about the structure of the mixed micelles. The α-methylene group of CTAB is in the near vicinity of the phenoxy ring of TX-100. The trimethyl group attached to the polar head of CTAB locates between the first oxyethylene group next to the phenoxy ring of TX-100, and the end methyl group of CTAB is close to those of TX-100. The closely packed (coiled) hydrophilic polyoxyethylene chains in the exterior part of the mixed micelles gradually extend with an increase in C/T in the mixed solution. CTAB and TX-100 molecules are uniformly mixed in the micelles in ...
TL;DR: High-performance liquid chromatography-mass spectrometry (HPLC-MS) analyses have led to the identification of several by-products as a result of simultaneous oxidation and substitution reactions, both occurring on the aromatic ring of the herbicide.
TL;DR: In this paper, a traveling molten zone (TZ) method was used to extract thallium bromide (TlBr) crystals for radiation detector applications, which were characterized in terms of their structural properties, stoichiometry and surface properties.
TL;DR: In this paper, the dyeing behavior of 1,4-diaminoanthraquinone on polyester fiber in the presence of two cationic gemini surfactants, propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (DC3-12) and hexanediymethyltrimethylammoniambromide (DC6-12), as auxiliaries, was investigated, and the results showed that dye which is solubilized within the surfactant mice