Reaction Of Bromide Ion Research Articles

Study of the bromide ion reaction with methyl naphthalene‐2‐sulfonate in water–DMSO TTAB micellar solutions

AbstractThe reaction of bromide ions with methyl naphthalene‐2‐sulfonate (MeNS) has been investigated in water–dimethyl sulfoxide, DMSO, tetradecyltrimethylammonium bromide, TTAB, micellar solutions, with the weight percentage of DMSO up to 50%. In order to quantitatively rationalize the micellar kinetic effects observed, conductivity, surface tension, and steady‐state fluorescence measurements were used to get information about the micellar reaction media. Results showed that changes caused by the addition of different amounts of DMSO to TTAB aqueous micellar solutions are made evident from the kinetic micellar effects, these being a helpful tool to obtain information on the micellar reaction media in the presence of the added organic solvent. Copyright © 2006 John Wiley & Sons, Ltd.

Formation of Bromate Ion Through a Radical Pathway in a Continuous Flow Reactor

ABSTRACT The contribution of ozone and hydroxyl radical to the formation of bromate ion was investigated in a continuous flow reactor. Experiments were conducted under a wide range of ozone dose (0.7 ∼ 3.8 mgL), pH (6.5 ∼ 8.5), and t-butanol concentration (0 ∼ 0.5 mM). The formation of bromate ion was found to depend on radical reaction pathway, because the amount of bromate ion formed increased with pH and decreased with t-butanol, a radical scavenger, even when dissolved ozone concentrations were almost the same. In fact, the amount of bromate ion formed was reduced by 90% in the presence of t-butanol. Furthermore, the formation of bromate ion occurred even when dissolved ozone was not significantly detected in the presence of organic matter (TOC of 1 mgCL). The second-order reaction rate constant of hydroxyl radical with bromide ion, k HO,Br− of 1.7 × 109 (M−1s−1), was obtained on the assumption that the reactions of bromide ion and t-butanol with hydroxyl radical were competitive with each other in the presence of t-butanol and that the formation of bromate ion depended on the reaction of bromide ion with hydroxyl radical. Therefore, it is concluded that the reaction of bromide ion with hydroxyl radical dominated in the overall reaction from bromide ion to bromate ion in the continuous flow reactor.

Flash photolytic generation and study of p-quinone methide in aqueous solution. An estimate of rate and equilibrium constants for heterolysis of the carbon-bromine bond in p-hydroxybenzyl bromide.

Flash photolysis of p-hydroxybenzyl acetate in aqueous perchloric acid solution and formic acid, acetic acid, biphosphate ion, and tris(hydroxymethyl)methylammonium ion buffers produced p-quinone methide as a short-lived species that underwent hydration to p-hydroxybenzyl alcohol in hydronium ion catalyzed (k(H(+)) = 5.28 x 10(4) M(-1) s(-1)) and uncatalyzed (k(uc) = 3.33 s(-1)) processes. The inverse nature of the solvent isotope effect on the hydronium ion-catalyzed reaction, k(H(+))/k(D(+)) = 0.41, indicates that this process occurs by rapid and reversible protonation of the quinone methide on its carbonyl carbon atom, followed by rate-determining capture of the p-hydroxybenzyl carbocation so produced by water, while the magnitude of the rate constant on the uncatalyzed process indicates that this reaction occurs by simple nucleophilic addition of water to the methylene group of the quinone methide. p-Quinone methide also underwent hydronium ion-catalyzed and uncatalyzed nucleophilic addition reactions with chloride ion, bromide ion, thiocyanate ion, and thiourea. The solvent isotope effects on the hydronium ion-catalyzed processes again indicate that these reactions occurred by preequilibrium mechanisms involving a p-hydroxybenzyl carbocation intermediate, and assignment of a diffusion-controlled value to the rate constant for reaction of this cation with thiocyanate ion led to K(SH) = 110 M as the acidity constant of oxygen-protonated p-quinone methide. In a certain perchloric acid concentration range, the bromide ion reaction became biphasic, and least-squares analysis of the kinetic data using a double-exponential function provided k(Br(-)) = 3.8 x 10(8) M(-1) s(-1) as the rate constant for nucleophilic capture of the p-hydroxybenzyl carbocation by bromide ion, k(ionz) = 8.5 x 10(2) s(-1) for ionization of the carbon-bromine bond of p-hydroxybenzyl bromide, and K = 4.5 x 10(5) M(-1) as the equilibrium constant for the carbocation-bromide ion combination reaction, all in aqueous solution at 25 degrees C. Comparisons are made of the reactivity of p-quinone methide with p-quinone alpha,alpha-bis(trifluoromethyl)methide as well as p-quinone methide with o-quinone methide.

Substituent effects on the spontaneous cleavage of α-methylbenzylgem- dichlorides in aqueous solution

The a-bromobenzyl cations have been produced in aqueous solution by chemical initiation (solvolysis) of benzyla-gem­ dibromides. The solvolysis reactions of benzyl-gem-dibromides in water proceed by a stepwise mechanism through a-bromobenzyl carbocation intermediates, which are captured by water to give the corresponding benzaldehydes as the sole detectable products. Rate constant ratios ks/k, (MI) for partitioning of the carbocation be­ tween reaction with bromide ion and reaction with water have been determined by analysis of bromide common ion inhibition of the solvolysis reaction . The rate constants k, (S'I) for the reaction of the cation with solvent water were determined from the ex­ perimental values of ks/k, and k,o lv. for the solvolysis of the ben­ zyl-gem-dibromides, using kSr = 5x 10 9 MI S· I for diffusion­ limited reaction of bromide ion with benzyl carbocations. Calcu­ lation and discussion of selectivities, ks/ks' of the a-bromobenzyl cations, activation parameters for solvolysis step and for addition of water to the cation are some of the salient features not reported earlier. Effect of substituents is also discussed in terms of Ham­ mett equation for both the steps. The substitution reactions of benzyl derivatives have been well-studied l ,2 and several investigations appeared in literature for the development of the the­ ory of nucleophilic substitution at saturated carbon l - 9 , In the study of solvolysis reactions of some benzyl­ chlorides, benzalchlorides and polychloromethyl ethers, it was concluded that these reactions proceed through stable carbocation intermediates, This was attributed to the contributions of additional structures in which positive charge is placed on a-chlorine lO , Also, there were few reports of salt and deuterium isotope effects on solvolytic reactions of benzalchlo­ rides in aquo-organic mixed solvents 11-13, This prompted us to investigate the solvolysis reactions of benzyl-gem-dibromides in aqueous solution with a view to find whether the developing bromobenzyl cation would be stabilized by the other bromo sub­ stituent. Experimental Inorganic salts and organic chemicals used for chemical syntheses were reagent grade and used as such, The water used for kinetic studies was distilled over acid dichromate and permanganate. The gem­ dibromides were synthesized as per a reported proce­ dure l4 , Solvolysis rate constants for the reaction of the benzyl-gem-dibromides were determined in water containing I % acetonitrile at 25°C and at a constant ionic strength of 1,0 M, maintained with NaCI04 . The stock solution of the substrate was prepared in aceto­ nitrile, The solvolysis reactions of benzyl-gem­ dibromides were initiated by making a 100-fold dilu­ tion of the stock solution of substrate in acetonitrile to the reaction mixture to give a final concentration of 1.0 x 10- 4 M by injecting 30 IJ.L to 3 mL of water

Studies on the oxidation of ?-amino acids by N-Bromo oxidants: Kinetics of the reaction of bromide ion with N-Bromoacetamide

The rate of oxidation of amino acids (AA) by N-Bromoacetamide (NBA) was studied in aqueous buffered medium at 35°C. The rate of disappearance of [NBA] is catalyzed by the Br− produced from the reduction of NBA. Analysis of the autocatalyzed reaction gives the kinetic data for the oxidation of bromide ion by NBA. The results suggest that the protonated NBA reacts with Br− to form Br2 which rapidly oxidizes amino acids. The rate constant for the reaction between protonated NBA and Br− at 35°C is estimated. © 1996 John Wiley & Sons, Inc.

Single-ion enthalpies of transfer as a scale of nucleophilic reactivity towards ethyl iodide in acetonitrile

Logarithmic rates for nucleophilic substitution towards ethyl iodide in acetonitrile correlate well with the specific interaction enthalpies for the relevant nucleophile, ΔHt,SIAN → MeOH(Nu–). According to the correlation, the bromide ion reaction falls into the imidide ion reaction series, while the chloride ion reaction falls into the carboxylate ion reaction series. The partial desolvation accompanying activation is crucial in determining the reactivity behaviour of the nucleophile anions. Semi-empirical quantum mechanical calculations (MNDO/PM3 and MNDO/PM3/COSMO) give reasonable estimates for the enthalpies of activation as well as for reaction enthalpies in acetonitrile. The relative location of the transition state, estimated on the basis of empirical analysis, is in accord with the variation of electronic charges for the exposed atoms, which has been evaluated through semi-empirical quantum mechanical procedures.

Anomalous salt effects on a micellar‐mediated reaction of bromide ion

AbstractReaction of bromide ion with α‐picryl‐p‐bromoacetophenone (1) is speeded by aqueous cationic micelles of cetyltrimethylammonium bromide (CTABr; C16H33NMe3Br) and dodecyltrimethylammonium bromide (DoTABr; C12H25NMe3Br) and rate constants reach limiting values when 1 is fully bound to micelles of CTABr. Limiting values are not reached in DoTABr, but the data can be fitted to a simple model for the distribution of reactants between water and micelles. Estimated second‐order rate constants at the micellar surface are similar to values in water, but this model cannot explain the observed rate enhancements on addition of NaBr to CTABr. Inert anions such as nitrate, mesylate, n‐butanesulfonate, phenylmethanesulfonate and camphor‐10‐sulfonate inhibit reaction in CTABr by competing with Br− at the micellar surface. Other n‐alkanesulfonate ions (RSO, R = n‐C5H11, n‐C6H13, n‐C7H15, n‐C8H17) and arenesulfonate ions (benzene‐, toluene‐, naphthalene‐1‐ and naphthalene‐2‐sulfonate) behave anomalously. These ions expel Br− from the micelle, as shown electrochemically, but there are maxima in plots of rate constant against mole fraction of Br−. These rate extrema are apparently due to perturbation of the micellar surface structure that overcomes the inhibition due to competition with Br−. These results show that the simple pseudo‐phase, ion‐exchange model can be applied only in dilute electrolyte and in the absence of hydrophobic anions.

Theoretical analysis of activation parameters in mixed solvents involving various chemical equilibria. Reaction of ethyl iodide with bromide ion in N-methylacetamide-acetonitrile and N-methylacetamide–N,N-dimethylacetamide mixtures

A theoretical equation has been developed for an activity coefficient of a solute dissolved in a mixed solvent based on the assumption of ideal associated mixtures, where three types of chemical equilibria proceed simultaneously, namely two types of equilibria between a solute and a further chemical species in a binary mixed solvent, and an association equilibria between the two component solvents. The derived equation was transformed into further theoretical equations for the rate constants and activation parameters for the ethyl iodide plus bromide ion reaction. The rate constants and activation parameters for the reaction determined in N-methylacetamide–acetonitrile and in N-methylacetamide–N,N-dimethylacetamide mixtures have been analysed by applying these equations.

Systematic design of chemical oscillators. Part 35. Kinetics and mechanism of the reaction between chlorine(III) and bromide ion

The stoichiometry and kinetics of the reaction between chlorine(III) and bromide ion were studied spectrophotometrically at 25.0 +/- 0.5 /sup 0/C and ionic strength 1.2 M (NaClO/sub 4/). The main products are Br/sub 3//sup -/ and Cl/sup -/ when bromide ion is in excess, ClO/sub 2/ and Br/sub 2/ when chlorine(III) is in excess. With sufficient acid and excess bromide ion, the stoichiometry of the reaction is HClO/sub 2/ + 6Br/sup -/ + 3H/sup +/ ..-->.. 2Br/sub 3//sup -/ + Cl/sup -/ + 2H/sub 2/O. The rate law for this reaction is (1/2)d(Br/sub 3//sup -/)/dt= k(H/sup +/)(Br/sup -/)(Cl(III)) where k = 9.51 +/- 0.14) x 10/sup -2/ M/sup -2/ s/sup -1/. When the reaction is carried out with (Cl(III)) > (Br/sup -/), the stoichiometry is difficult to define. In the range (Cl(III)) approx. = (1.50 - 2.00) x 10/sup -3/ M, (Br/sup -/) approx. = 5.00 x 10/sup -4/ M, and (perchloric acid) approx. = 0.20 M, a clock reaction occurs, the lag time of which decreases with addition of small amounts (<10/sup -4/ M) of molecular bromine. The complex rate law for the chlorine(III)-bromide ion reaction with excess Cl(III) can be explained by a 16-step mechanism including oxidation ofmore » bromide ion to bromine by chlorine(III), reduction of bromine to bromide ion, and decomposition of chlorous acid. A reduced set of 10 reactions and associated rate and equilibrium constants successfully modeled the clock reaction by computer simulation.« less

Characterization of anion solvation in N-methylacetamide. Transfer enthalpies of anions and the reaction rates of ethyl iodide with bromide ion in N-methylacetamide–acetonitrile and N-methylacetamide–N,N-dimethylacetamide mixtures

Single-ion transfer enthalpies have been determined in N-methylacetamide–acetonitrile and N-methylacetamide–N,N-dimethylacetamide mixtures for bromide, perchlorate, and tetra-n-butylborate ions on the basis of the tetra-n-butylammonium/tetra-n-butylborate assumption. From both empirical and theoretical treatments of these quantities it is concluded that N-methylacetamide interacts with these spherical and pseudo-spherical anions through the N—H dipole directed towards the anion, i.e. it behaves as a protic solvent. Transfer enthalpies for the transition-state anion have also been determined for the ethyl iodide plus bromide ion reaction in the two solvent mixtures. The presence and the magnitude of the specific interaction between the rod-like transition-state anion and the amide linkage, due to dipole–dipole association, have been evaluated on various grounds. The relative alignment of N-methylacetamide towards the anion seems to change as the reaction proceeds from reactants to a transition state.

Effects of preferential solvation and of solvent–solvent interaction on the rates of nucleophilic substitution involving anions in binary mixed solvents. Theoretical approach

Theoretical procedures for investigating rate constants and activation parameters measured in binary mixed solvents have been presented on the basis of the concept of ideal associated mixtures. In methanol + acetonitrile mixtures the behaviour of the rate constant and of activation parameters for the ethyl iodide plus bromide ion reaction were interpreted as resulting from the specific interaction of bromide ion with methanol. In methanol +N N-dimethylacetamide mixtures association complex formation between methanol and N N-dimethylacetamide makes a significant contribution to the activation parameters, and this factor must be taken into account in interpreting the observed rate behaviour.

Kinetic investigation of the bromate–ascorbic acid–malonic acid system

AbstractAccording to our experiments the bromide ion concentration exhibits in the bromate–ascorbic acid–malonic acid–perchloric acid system three extrema as a function of time. To describe this peculiar phenomenon, the kinetics of four component reactions have been studied separately. The following rate equations were obtained:Bromate–ascorbic acid reaction: Bromate–bromide ion reaction: Bromide–ascorbic acid reaction: Bromine–malonic acid reaction: k4 = 6 × 10−3 s−1, k‐4 ≥ 1.7 × 103 s−1, k5 ≥ 1 × 107M−1 · s−1Taking into account the stoichiometry of the component reactions and using these rate equations, the concentration versus time curves of the composite system were calculated. Although the agreement is not as good as in the case of the component reactions, it is remarkable that this kinetic structure exhibits the three extrema found.

An adduct of hydrogen bromide and ferrous phthalocyanine

Ferrous phthalocyanine (FePc) and concentrated hydrobomic acid react giving a 1:1 FePc-HBr adduct. In aprotic solvents adduct formation is reversable and is a reaction of bromide ion with protonated phthalocyanine.