Bromide Ion (bromide + ion)

Distribution by Scientific Domains


Selected Abstracts


SN2 Displacement by Bromide Ions in Dichloromethane , The Role of Reverse Micelles

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006
Lucia Brinchi
Abstract Reverse micellar systems are of interest as reaction media because they are powerful models for biological compartmentalization, enzymatic catalysis and separation of biomolecules. Solutions of ionic surfactants in apolar solvents may contain reverse micelles, but they may also contain ion pairs, or small clusters, with waters of hydration. We studied the bimolecular reaction in CH2Cl2 solutions of cationic tetraalkylammonium bromide salts (onium salts), such as cetyltrimethylammonium bromide (CTABr), cetyltripropylammonium bromide (CTPABr) and tetra- n -butylammonium bromide (TBABr). Methylnaphthalene-2-sulfonate (,-MeONs), its 6-sulfonate derivative (,-MeONsS,) as the 2,6-lutidinium salt and methyl-5- N,N,N,trimethylammonium naphthalene-1-sulfonate (,-MeONsNT+) as the trifluoromethanesulfonate salt react with Br, in CH2Cl2. First-order rate constants, kobs, increase linearly and similarly for the three substrates with increasing concentrations of the onium salts. Reactions are faster with TBABr than they are with CTPABr and CTABr, and the reactivity of the three substrates is in the order: ,-MeONsNT+ >> ,-MeONsS, > ,-MeONs. The reactions are inhibited by the addition of H2O, but CTABr tolerates H2O in large excess. At [H2O]/[CTABr] = w0 , 6, "water-pool" reverse micelles form, and kobs for all three substrates is then independent of w0. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


The Interaction of Bromide Ions with Graphitic Materials,

ADVANCED MATERIALS, Issue 1 2009
Apurva Mehta
The detailed interactions between hydrated bromine ions and a number of graphene-like surfaces are elucidated for the first time. A common edge site that exhibits preferential binding of bromide is observed for all materials. The local structure around the hydrated bromide in this interaction region is that of the ion binding to a zigzag, convex site on the graphene sheet edge, consistent with predictions of a recent theoretical model. [source]


The relationship between disinfection by-product formation and structural characteristics of humic substances in chloramination

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2003
Wells W. Wu
Abstract The influence of structural characteristics of humic substances on disinfection by-product (DBP) formation was investigated for seven humic substances isolated from aquatic and terrestrial sources. The structural characterizations included 13C nuclear magnetic resonance (13C NMR) spectroscopy and ultraviolet (UV) spectroscopy. The aqueous humic substances were chloraminated at pH 7.0 and 8.5, with and without the presence of the bromide ion, and analyzed for total organic halogen (TOX), trihalomethanes (THMs), and haloacetic acids (HAAs). Aromatic contents determined by 13C NMR and differential UV absorbance at 254 nm statistically correlated with TOX formation for the humic substances investigated at p < 0.08. In contrast, a lack of correlation was observed for THM and HAA formation and these parameters. This paper also compiles relevant literature and discusses the contrasting reaction response of DBP precursor material to chlorination and chloramination. [source]


Diastereopure Cationic NCN-Pincer Palladium Complexes with Square Planar ,4 - N,C,N,O Coordination

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2006
Silvia Gosiewska
Abstract Neutral NCN-pincer palladium bromide complex 2 containing the monoanionic, enantiopure pincer ligand 2,6-bis{[(S)-2-hydroxymethyl-1-pyrrolidinyl]methyl}phenyl bromide (1) with bis- ortho -(S)-prolinol substituents was synthesized and isolated as a mixture of three stereoisomers [(SN,SN,SC,SC), (RN,SN,SC,SC), and (RN,RN,SC,SC)] in a 1:1:1 ratio. Upon abstraction of the bromide ion from the unresolved mixture of 2, single diastereoisomers of the cationic complexes [3]BF4 and [3]PF6, respectively, were formed with a unique,4 - N,C,N,O coordination mode of ligand 1. X-ray crystal structure determination established the intramolecular,4 - N,C,N,O coordination of 1 to palladium where the typical mer -,3 - N,C,N pincer coordination is accompanied by coordination of one of the hydroxy groups of the (S)-prolinol moieties. The water molecule that was cocrystallized in the crystal structure of [3]PF6 does not coordinate to palladium, but instead is involved in a hydrogen bonding network. The catalytic potential of both cationic complexes, [3]BF4 and [3]PF6, was tested in an aldol reaction of aldehydes with methyl isocyanoacetate to yield the oxazoline products as racemic mixtures.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


A Simple and Convenient Method for Epoxidation of Olefins without Metal Catalysts

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2003
Markus Klawonn
Abstract An easy method for epoxidation of olefins using bleach (sodium hypochlorite) and either a stoichiometric or catalytic amount of bromide ion has been developed. Without any transition metal catalyst a variety of non-activated olefins give epoxides in high yields and good selectivity at ambient conditions. [source]


Kinetics of reactions between chlorine or bromine and the herbicides diuron and isoproturon

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 2 2007
Juan L Acero
Abstract The chemical oxidation of two herbicide derivatives of the phenylurea group,diuron and isoproturon,has been carried out by means of chlorine, in the absence and in the presence of bromide ion. Apparent second-order rate constants for the reactions between chlorine and the herbicides were determined to be below 0.45 L mol,1 s,1. Hypobromous acid reacts faster with the investigated herbicides, especially with isoproturon (kapp = 24.8 L mol,1 s,1 at pH 7). While pH exerts a negative effect on the bromination rate, the maximum chlorination rate was found to be at circumneutral pH. In a second stage, the oxidation of each compound was conducted in different natural waters, in order to simulate the processes which take place in water purification plants. Again, chlorine was used as an oxidant, and bromide ion was added in some experiments with the aim of producing the more reactive HOBr oxidant. The herbicide oxidation rate was inversely proportional to the organic matter content of the natural water. However, the formation of trihalomethanes (THMs) was directly proportional to the organic matter content and constitutes a limitation for the application of chlorine during drinking water treatment. Finally, the evolution of herbicide concentration was modeled and predicted by applying a kinetics approach based on the rate constants for the reactions between the herbicides and the active oxidants. Copyright © 2007 Society of Chemical Industry [source]


SN2 reaction of a sulfonate ester in the presence of alkyltriphenylphosphonium bromides and mixed cationic-cationic systems

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2006
Michael M. Mohareb
Abstract The effects of alkyltriphenylphosphonium bromides (CnTPB, n,=,10, 12, 14, 16) on the rates of SN2 reactions of methyl 4-nitrobenzenesulfonate and bromide ion have been studied. Observed first-order rate constants are significantly higher than those found for other cationic surfactants for the same reaction. The results have been analyzed by the pseudophase model of micellar kinetics and show true micellar catalysis in the sense that second-order micellar rate constants are higher than the second-order rate constants in water. An attempt has also been made to investigate mixed cationic,cationic surfactant systems with respect to observed rates and pseudophase regression parameters. In addition, modeling of some cationic head groups has illustrated possible differences in head group charges and counterion interactions that may prove kinetically relevant. Copyright © 2006 John Wiley & Sons, Ltd. [source]


Solvolysis of chiral cyclohexylidenemethyl triflate.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8 2002
Evidence against a primary vinyl cation intermediate
Abstract Solvolysis of (R)-4-methylcyclohexylidenemethyl triflate (6) was examined at 140,°C in various aqueous methanol and some other alcoholic solvents. The main product was (R)-4-methylcycloheptanone that maintains the stereochemical purity of 6, with accompanying 4-methylcyclohexanecarbaldehyde. In the presence of bromide ion, the bromide substitution product was also obtained, mostly with inversion of configuration. It is concluded that the solvolysis does not involve the formation of the primary vinyl cation but proceeds via ,-bond participation to form the rearranged cycloheptenyl cation as an intermediate. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Deep Blue Mixed-Valent PtIIIPtIIIPtII Complex [Pt3Br2(,-pz)6] (pz=Pyrazolate) Showing Valence-Detrapping Behavior in Solution

CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2006
Keisuke Umakoshi Prof. Dr.
Abstract The oxidation of the pyrazolate bridged cyclic PtII trimer, [Pt3(,-pz)6] (1), in the presence of bromide ion gave a deep blue mixed-valent PtII,III,III complex, [Pt3Br2(,-pz)6] (2). The structural analysis of 2 disclosed that the complex has localized PtPt bond. Our theoretical calculations revealed that the HOMO and LUMO of Pt3II,III,III species mainly consists of (d,,d,) and (d,,d,)* orbitals, respectively, and the origin of deep blue color of the bromo complex, 2, arises from the (d,,d,),(d,,d,)* transition. Unique fluxional behavior was observed due to valence-detrapping of 2 in solution. The activation parameters of the valence-detrapping of 2 obtained by Eyring analyses were ,H,=37(2) kJ,mol,1 and ,S,=,67(7) J,mol,1,K,1. [source]


Surfactant-Assisted Preparation of Novel Layered Silver Bromide-Based Inorganic/Organic Nanosheets by Pulsed Laser Ablation in Aqueous Media,

ADVANCED FUNCTIONAL MATERIALS, Issue 17 2007
C. He
Abstract A novel layered AgBr-based inorganic/organic nanocomposite was prepared by pulsed laser ablation (PLA) of Ag in aqueous media in the presence of cetyltrimethylammonium bromide (CTAB), and the formation mechanism of two-dimensional nanosheet was discussed. TEM observations indicate that the obtained AgBr-based inorganic/organic nanocomposite possesses a well-defined two-dimensional shape and that the size of the nanosheet can be changed with the surfactant concentration in the solution. X-ray diffraction (XRD) pattern was composed of a series of peaks that could be indexed to (00l) reflections of a layered structure, and the basal spacing of 20.0,Å indicated that the surfactant was included between the AgBr interlayers in an interdigitated bilayer arrangement. In contrast, a layered inorganic/organic nanocomposite cannot be formed at a CTAB concentration lower than the critical micelle concentration (CMC). Based on our detailed investigation, we proposed the nanocomposite formation process, that is, that negatively charged inorganic AgBr was produced by a strong reaction between the ablated Ag species and the bromide ions, which are concurrently assembling with cationic surfactant molecules controlled by the charge-matching mechanism. [source]


Pitting corrosion on 316L pipes in terephthalic acid (TA) dryer

MATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 11 2009
Y. Gong
Abstract Grade 316L is a type of austenitic stainless steel with ultra-low carbon content and it exhibits superior corrosion resistance. However, pitting is always observed in 316L steel when it is exposed to media containing halide ions. In the present study, we found that in the presence of acetate acid (HAc) containing chloride or bromide ions, pitting occurred on the surface of the rotary steam pipes with the matrix material of 316L steel in terephthalic acid (TA) dryer. In order to identify the causes of the failure, metallographic structures and chemical compositions of the matrix material were inspected by an optical microscope (OM) and a photoelectric direct reading spectrometer. Beside these, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) as well as ion chromatography (IC) were used to analyze the micromorphologies of the corrosion pits and the chemical compositions of the corrosion deposits within them. Analysis of the results revealed the sources of halide ions and the factors accelerating the corrosion rate. Beside these, detailed mechanisms of pitting were discussed and six out of all the seven theoretical morphologies of pitting features were obtained in practice. [source]


Partial Oxidation of 4- tert -Butyltoluene Catalyzed by Homogeneous Cobalt and Cerium Acetate Catalysts in the Br,/H2O2/Acetic Acid System: Insights into Selectivity and Mechanism

CHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2007

Abstract The partial oxidation of 4- tert -butyltoluene to 4- tert -butylbenzaldehyde by hydrogen peroxide in glacial acetic acid, catalyzed by bromide ions in combination with cobalt(II) acetate or cerium(III) acetate, has been studied in detail. Based on the observed differences in reaction rates and product distributions for the different catalysts, a reaction mechanism involving two independent pathways is proposed. After the initial formation of a benzylic radical species, either oxidation of this intermediate by the metal catalyst or reaction with bromine generated in situ occurs, depending on which catalyst is used. The first pathway leads to the exclusive formation of 4- tert -butylbenzaldehyde, whereas reaction of the radical intermediate with bromine leads to formation of the observed side products 4- tert -butylbenzyl bromide and its hydrolysis and solvolysis products 4- tert -butylbenzyl alcohol and 4- tert -butylbenzyl acetate, respectively. The cobalt(II) catalysts Co(OAc)2 and Co(acac)2 are able to quickly oxidize the radical intermediate, thereby largely preventing the bromination reaction (i.e., side-product formation) from occurring, and yield the aldehyde product with 75,80,% selectivity. In contrast, the cerium catalyst studied here exhibits an aldehyde selectivity of around 50,% due to the competing bromination reaction. Addition of extra hydrogen peroxide leads to an increased product yield of 72,% (cerium(III) acetate) or 58,% (cobalt(II) acetate). Product inhibition and the presence of increasing amounts of water in the reaction mixture do not play a role in the observed low incremental yields. [source]


Bleaching of indigo-dyed denim fabric by electrochemical formation of hypohalogenites in situ

COLORATION TECHNOLOGY, Issue 2 2005
Thomas Bechtold
The use of hypochlorite, formed in situ by anodic oxidation of sodium chloride solution, for bleaching indigo-dyed denim has been studied at room temperature and at 50 °C. A direct relationship between the charge flow applied and the bleaching effect was observed. This enables consistent oxidative bleaching to be achieved by controlling the electrochemical process. The use of mixed anolytes containing small concentrations of bromide ions enhanced the bleaching effect considerably, even after lowering the temperature to room temperature. The molar concentration of bromide ions required was much lower than that of chloride in the anolyte. [source]