BrCl Research Articles

Kinetic and mechanistic study of the reaction of atomic chlorine with methyl bromide over an extended temperature range

A laser flash photolysis–resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with methyl bromide as a function of temperature (161–697 K) and pressure (20–250 Torr) in nitrogen buffer gas. At T≥213 K, where information available in the literature suggests that hydrogen transfer is the dominant reaction pathway, observed rate coefficients are pressure independent and the following modified Arrhenius expression adequately describes all kinetic data obtained: k 1a=1.02×10 −15 T 1.42 exp(−605/ T) cm 3 molecule −1 s −1. At temperatures in the range 161–177 K, reversible addition of Cl( 2P J ) to CH 3Br is observed, thus allowing rate coefficients and equilibrium constants for CH 3BrCl formation and dissociation to be determined. Second- and third-law analyses of the equilibrium data lead to the following thermochemical parameters for the association reaction (1d): Δ H 298 o=−25.6±2.3 kJ mol −1, Δ H 0 o=−24.0±2.9 kJ mol −1, Δ S 298 K o=−72.3±11.8 J K −1 mol −1. In conjunction with the well-known heats of formation of Cl( 2P J ) and CH 3Br, the above Δ H values lead to the following heats of formation for CH 3BrCl at 298 and 0 K: Δ H f, 298 o=57.6±2.4 kJ mol −1 and Δ H f, 0 o=72.9±3.0 kJ mol −1. Ab initio calculations using density functional theory and G2 theory reproduce the experimental bond strength reasonably well. The DFT calculations predict a CH 3BrCl structure (used in the third-law analysis) where the C–Br–Cl bond angle is 90° and the methyl group adopts a staggered orientation with a pronounced tilt toward chlorine. Ab-initio calculations are also reported which examine the structures and energetics of adducts formed from addition of F atoms and OH radicals to CH 3Br. Structures of CH 3BrF and CH 3BrOH are similar to that of CH 3BrCl, with the F-adduct being the most strongly bound and the OH-adduct being the least strongly bound. Bonding in CH 3Br–X (X=F, Cl, OH) is discussed as are the implications of the new experimental and theoretical results for atmospheric chemistry.

Organophosphorus Compounds; 124. Phosphorus-Phosphorus Bond Cleavage in Phosphorus-Carbon Cage Compounds Containing a Diphosphirane Moiety

The reactions of diphosphatricyclooctenes 9 with bromine (10 a) or iodine chloride (10 b) proceed by selective cleavage of the phosphorus-phosphorus bond of the diphosphirane unit with formation of the diphosphabicyclooctenes 11. On reaction of 11 a with one equivalent of nonacarbonyldiiron (12) metal complexation of one phosphorus center (→ 13 a) is achieved. The constitution of the η 1-complex 13 a was confirmed by X-ray crystallography.

Computational Comparison of SN2 Substitution Reactions of CHX•- and CH2X- with CH3X (X = Cl, Br). Do Open-Shell and Closed-Shell Anions React Differently?

The S(N)2 displacement reaction of the radical anions (CHCl(*-) and CHBr(*-)) and the closed-shell anions (CH(2)Cl(-) and CH(2)Br(-)) with CH(3)Cl and CH(3)Br were studied with density functional theory. It was determined that the anions CH(2)Cl(-) and CH(2)Br(-) were more reactive than the radical anions CHCl(*-) and CHBr(*-), in agreement with experiment. The degree of charge transfer in the reactant complex is the best indicator of the reactivity trend. It was found that two reactions (CH(2)Cl(-) with CH(3)Cl and CH(3)Br) proceeded without an activation barrier at the B3LYP/6-31+G(d) level. The backside transition states (leading to inversion of configuration at the methyl group) were 20-30 kcal/mol lower in energy than the frontside transition states (leading to retention of configuration). Interestingly, it was found that the mechanism of backside and frontside attack by radical anions was different. In backside attack, the radical anion leads with the lone pair directed toward the methyl group to form an incipient two-center, two-electron bond. In frontside attack, the radical anion leads with the unpaired electron directed toward the methyl group to form an incipient two-center, one-electron bond.

σ,π Interaction in Halogen-Substituted Biadamantylidene Radical Cations

The order of E°‘ and vIP for 4-eq-halogenated-biadamantylidene is F > Cl Br, and the 5-F-substituted compound is harder to ozidize than the 4-eq-F-substituted one. The former result is most consistent with a detectable resonance contribution through the σ-framework, and the latter with σ-hyperconjugative destablilization proceeding through two pathways being more than double the same effect through one pathway (the Whiffen effect). AM1 calculations predict these results. The facial selectivity for epoxidation and diazetidine formation from 4-eq-halogenated 3 (4(X)) is in the order Cl > F > Br, and the 5-fluoro compound (8) is less selective than 4(F) for both reactions. Steric as well as electronic factors might well contribute to these results, neither of which was expected from consideration of σ,π interaction. Cation radical catalyzed chain dioxetane formation from 4(F) and 3(Cl) is significantly more face selective than epoxidation or diazetidine formation, as expected on electronic grounds; σ,π interaction should be larger in the radical cation.

Calibration of [formula omitted] fractionation during subcritical phase separation of seawater: Possible halite at 9 to 10°N East Pacific Rise

Experiments were conducted to assess Br Cl fractionatiodn during phase separation of seawater at 400°C and 250 to 275 bars. These conditions are applicable to the 9–10°N EPR system where low Cl concentrations and low Br Cl rations in vent fluids have been attributed to phase separation of seawater at conditions below the critical point of seawater (408°C, 300 bars). The level of Br Cl fractionation observed in experiments is well below that needed to account for Br Cl systematics at EPR 9–10°N. Based on our experimental results, we propose an alternative model involving dissolution and precipitation of halite to account for the anomalous Br Cl data at 9–10°N. Halite can be predicted to form at pressure and temperature conditions prevailing during eruption of magma at mid-ocean ridges. Subsequent changes in physical conditions, however, would induce halite to dissolve, and thus, decrease Br Cl ratios of vent fluids.

Application of Gaussian-2 theory for the energetics of XO/XO+/XO- and XOH/XOH+ (X = F, Cl, Br, I)

The Gaussian-2 (G2) procedure, with spin-orbit coupling correction estimated by the Breit-Pauli approach, is applied to study the energetics of XO/XO+/XO- and XOH/XOH+(X = F Cl Br, I). Accurate thermochemical data for these environmentally important species, in particular for the anions and iodine containing species, have not been accurately determined experimentally. For example, for IO the reported experimental heat of formation varies from -109 kJ mol-1 to 177 kJ mol-1 Using the G2 results it is now possible to recommend a set of self-consistent thermochemical data of heats of formation, ionization energies, electron affinities, proton affinities and bond dissociation energies for XO and related species. In general, among the disparate experimental data, the more recently reported heats of formation for FO-, BrO+, BrO-, BrOH, BrOH+, IO, IO+, IO-, IOH, IOH+ are found to be in good agreement with the G2 results.

Application of Gaussian-2 theory for the energetics of XO/XO+ /XO- and XOH/XOH+ (X = F, Cl, Br, I)

The Gaussian-2 (G2) procedure, with spin-orbit coupling correction estimated by the Breit-Pauli approach, is applied to study the energetics of XO/XO+/XO- and XOH/XOH+(X = F Cl Br, I). Accurate thermochemical data for these environmentally important species, in particular for the anions and iodine containing species, have not been accurately determined experimentally. For example, for IO the reported experimental heat of formation varies from -109 kJ mol-1 to 177 kJ mol-1 Using the G2 results it is now possible to recommend a set of self-consistent thermochemical data of heats of formation, ionization energies, electron affinities, proton affinities and bond dissociation energies for XO and related species. In general, among the disparate experimental data, the more recently reported heats of formation for FO-, BrO+, BrO-, BrOH, BrOH+, IO, IO+, IO-, IOH, IOH+ are found to be in good agreement with the G2 results.

The stability of aqueous silver bromide and iodide complexes at 25–300°C: Experiments, theory and geologic applications

The solubilities of AgBr (s) in NaBr solutions and AgI (s) in NaI solutions were measured at elevated temperature. Referring to the following general reactions (where X = Cl, Br, or I): AgX (s) ⇋ Ag + + X − (1) AgX (s) ⇋ AgX (aq) (2) AgX (s) + X − ⇋ AgX 2 − (3) AgX (s) + 2X − ⇋ AgX 3 2− (4) the following equilibrium constants were obtained: log K 2,Br = −4.01 ± 0.20 (200°C) and −3.12 ± 0.20 (300°C); log K 3,Br = −1.81 ± 0.10 (200°C) and −1.01 ± 0.10 (300°C); log K 3,I = −2.46 ± 0.20 (150°C), −1.92 ± 0.20 (200°C) and −1.47 ± 0.10 (250°C); and log K 4,I = −1.9 ± 0.4 (150°C) and −2.2 ± 0.4 (200°C). These results were combined with previously published data and our own extrapolations to obtain smoothed equilibrium constants at 25–300°C for reactions (1)–(4) at 25–300°C. Values of log K 1 and log K 2 at any given temperature decrease in the order X = Cl > Br > I, whereas the opposite trend is shown for log K 4 at 18°C. Values of log K 3 are similar for X = Cl, Br, I at all temperature, with Δ r H° = +40.7 to + 45.9 kJ mol −1. The enthalpies of reactions 2 Br and 2 Cl are also similar ( Δ r H° = +56.0 and +54.1 kJ mol −1, respectively). Conversion of the above data to cumulative formation constants ( β i , i = 1, 2, 3) indicates that the bromide and iodide complexes of silver are much stronger than their chloride counterparts. However, chloride complexes will dominate silver transport in most cases, due to the low Br Cl and I Cl ligand ratios of natural waters. Exceptions include certain oil field brines with I Cl > 10 −3 , in which case iodide or mixed chloride-iodide complexes become the dominant silver species. Our calculations indicate that AgI (s) is many orders of magnitude less soluble than AgCl (s) in connate brines, and may be an important solubility-limiting phase in sedimentary basins. AgI (s) may also form in the weathering environment, especially in the supergene zones of silver-rich hydrothermal mineral deposits, although AgCl (s) is more stable at Eh conditions above the aqueous I − IO 3 − boundary. Except in very unusual circumstances, silver halide minerals with be too soluble to precipitate directly from high-temperature hydrothermal fluids.

Mississippi valley-type mineralization in the Silurian paleoaquifer, central appalachians

This study used lead and sulfur isotope tracers to determine the nature and geometry of MVT-related brine flow in the Silurian paleoaquifer of the central Appalachians. Although the stratigraphy and lithology of this sedimentary package is similar to that of the important Lower Cambrian MVT-hosting paleoaquifer of the southern Appalachians, it lacks important mineralization. Lead isotope compositions from MVT deposits in the Lockport Dolomite, in the upper part of the Silurian paleoaquifer, form a cluster at about 206Pb 204Pb = 18.3 , 207Pb 204Pb = 15.6 , and 208Pb 204Pb = 38.2 , which is similar in form but slightly different in composition from those seen in deposits in underlying clastic rocks. Sulfur isotope compositions for Lockport MVT sulfides range from −19 to −6‰, and have lower δ 34S values than MVT sulfides hosted by underlying clastic rocks. These relations, in combination with NaClBr compositions of fluid inclusion leachates, suggest that MVT deposits in the lower part of the paleoaquifer formed when rising metal-bearing brines intersected reduced sulfur of probable thermogenic origin, whereas deposits in the upper part of the paleoaquifer (Lockport Dolomite) formed where metal-bearing brines intersected reduced sulfur of biogenic origin that was dissolved from sulfate evaporites in the overlying Salina Group and transported downward into the Lockport.

Reactions of ap- and sp-1-(9-Fluorenyl)-2-(1-methylethenyl)naphthalene Rotamers with Bromine Chloride or Iodine Chloride and Unusual Populations of the Corresponding 1-(9-Fluorenyl)-2-[(E)-2-halo-1-methylethenyl]naphthalene Rotamers

Abstract Reactions of bromine chloride and iodine chloride with the olefinic bond in 1-(9-fluorenyl)-2-(1-methylethenyl)naphthalene rotamers were carried out to examine the product distributions. In the case of the ap-isomer bromine chloride yielded some bromo-olefins in addition to the addition product, whereas the yield of (8R*,14cS*)-8-bromomethyl-8-methyl-8,14c-dihydrodibenzo[a.l]aceanthrylene from the sp-isomer diminished with respect to the case of the reaction between bromine and the sp-isomer. The results are attributed to the low nucleophilicity and high proton affinity of the chloride ion. Iodine chloride afforded more addition product for the ap-isomer than the case of bromine chloride, whereas the sp-isomer reacted with iodine chloride to give a better yield of a cyclized compound, (8R*,14cS*)-8-iodomethyl-8-methyl-8,14c-dihydrodibenzo[a,l]aceanthrylene, than that of the cyclized compound from bromine chloride. Such results are attributed to the better stabilizing effects of an iodo substituent on a β-carbocation than a bromo one. Populations of ap and sp rotamers of 1-(9-fluorenyl)-2-[(E)-2-halo-1-methylethenyl]naphthalenes at equilibrium were unusual in the sense that the ap-isomer of the sterically more crowded iodo compound was favored relative to the less crowded chloro compound. UV absorption spectra were not conclusive for charge transfer interactions but X-ray crystallography of these compounds revealed that the olefinic carbons in the ethenyl group were attracted to the fluorene ring significantly.

High bromine contents and low [formula omitted] ratios in hydrothermally altered Archaean komatiitic rocks, West Greenland

In Archaean supracrustal rocks in West Greenland komatiitic and tholeiitic rocks have undergone alteration by circulating hydrothermal solutions, whereby the rocks were partly transformed into calc-silicate assemblages. The alteration, which also formed extensive stratabound scheelite mineralizations, took place partly at the sea floor and partly below the sea floor prior to metamorphism and deformation of the volcano-sedimentary pile. The altered komatiitic and tholeiitic rocks contain up to 418 ppm bromine and Cl Br ratios down to 1.6 compared with 60–1300 ppb bromine and Cl Br ratios of 430 in mid-ocean ridge basalts. Cl and Br was not detected by electron microprobe in any of the minerals found. It is suggested that the volcano-sedimentary pile was altered by hot brines which had attained high halogen contents by reaction with mafic and ultramafic rocks. During brine-rock interaction the Cl Br ratio of the brines decreased and the metal contents increased. The metalliferous bromine-enriched brines ascended towards the sea floor. The bromine and some of the metals precipitated in the upper part of the volcano-sedimentary pile and in the volcanic rocks at the sea floor. High bromine contents and low Cl Br ratios may indicate presence of major orebodies.

Ethene stabilised by halogens on Cu(111)

Temperature-programmed desorption studies have been carried out for a range of initial coverages of ethene adsorbed on equimolar chlorine and bromine covered Cu(111) surfaces (0–0.33 ML total halogen coverage) at 100 K. For the clean surface, ethene had an activation energy for desorption of 29±2 kJ mol −1 at zero coverage, which decreased for increasing coverage, dropping to ∼27±2 kJ mol −1 for the highest coverage attainable at 103 K (using a fixed pre-exponential factor of 1 × 10 13 s −1). Chemisorbed chlorine and bromine stabilised the adsorbed ethene, the maximum effect occurring at 0.17 ML of Cl Br where the sticking probability increased to 1.4, and the saturation coverage to 2.5 times that of the clean surface at 103 K. At a combined Br Cl coverage of 0.25 ML, a particularly stable surface was formed for which the activation energy for ethene desorption was almost constant at 35±2 kJ mol −1. The ethene is thought to be coplanar with the halogens and bonded directly to the copper via its π orbital.

Hydrogen and oxygen isotope evidence for origin of MVT-forming brines, southern Appalachians

Hydrogen and oxygen isotope compositions of fluid inclusion hosted brines from Mississippi Valley type (MVT) deposits in the southern Appalachians were analyzed to test whether the dominant water in the brines was seawater as suggested by previously reported NaClBr relations. Measurements were made for deposits in the two main paleoaquifers in the area, the Lower Cambrian Shady and Lower Ordovician Knox, and included the large East Tennessee ore field and the Austinville district. δ 18O and δD values for sphalerite-hosted brines in the two main paleoaquifers cluster in separate fields. Those in the Lower Cambrian paleoaquifer form an elongate array that extends from δ 18O = 2% and δD = −41% to δ 18O = 5% and δD = −87%0. Those in the Lower Ordovician paleoaquifer form a cluster at about δ 18O = 7% and δD = −35%. Stable isotope compositions of fluid inclusion-hosted brines in fluorite from the Lower Ordovician paleoaquifer form an array that extends from the Lower Ordovician-hosted sphalerite cluster toward the composition of modern formation waters in the Lower Ordovician paleoaquifer, which plot along the meteoric water line. Stable isotope compositions of fluids in barite form an array that extends toward very low SD values typical of organic matter or gas. These data permit, but do not require, the interpretation that the mineralizing brines contain seawater with hydrogen and oxygen isotope compositions that were modified by reaction with country rocks, particularly with organic matter and/or hydrocarbon gas. When the Appalachian data are plotted together with those from other MVT districts in the mid-continent, the combined data form a broad array that extends downward from hydrogen and oxygen isotope compositions typical of seawater, toward low δD values such as would form by fluid interaction with organic matter or gas. Consideration of published isotopic compositions of brines from other MVT deposits suggests that interaction with organic matter and/or gas may be an important process in the evolution of ore-forming brines.

Structure and selective visible photodissociation of the O 3:Br 2 and O 3:BrCl complexes: An infrared matrix isolation and ab initio study

Complexes of ozone with chlorine, bromine and bromine chloride were reinvestigated in argon matrix by Fourier Transform Infrared spectroscopy. All three ozone submolecule fundamentals were observed and ν 1 was enhanced in intensity relative to ν 3. The asymmetric mixed isotopic ozone complexes exhibit a split ν 3 band which indicates unequivalent terminal oxygens. Photolysis of the O 3/BrCl system which was studied with the 870, 633 and 532 nm laser lines gives only ClBrO as a primary product indicating that the most stable complex between BrCl and O 3 occurs through bonding of ozone with Br. Results show that at 633 nm, ClBrO transforms it into BrClO whereas at 870 nm, it is isomerized to BrOCl. Ab initio calculations undertaken on the structures of O 3:Cl 2 and O 3:BrCl support experimental observations.

ChemInform Abstract: Si‐C Bond Cleavage in 1‐Organylsilatranes by Bromine or Iodine Chloride.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Resolution of matrix effects on analysis of total and methyl mercury in aqueous samples from the Florida Everglades

Aqueous samples from the Florida Everglades present several problems for the analysis of total mercury (HgT) and methyl mercury (MeHg). Constituents such as dissolved organic carbon (DOC) and sulfide at selected sites present particular challenges due to interferences with standard analytical techniques. This is manifested by 1) the inability to discern when bromine monochloride (BrCl) addition is sufficient for sample oxidation for HgT analysis; and 2) incomplete spike recoveries using the distillation/ethylation technique for MeHg analysis. Here, we suggest ultra-violet (UV) oxidation prior to addition of BrCl to ensure total oxidation of DOC prior to HgT analysis and copper sulfate (CuSO4) addition to aid in distillation in the presence of sulfide for MeHg analysis. Despite high chloride (Cl-) levels, we observed no effects on MeHg distillation/ethylation analyses.

Darstellung, 19F- und 195Pt-NMR-Spektren, Schwingungsspektren und Normalkoordinatenanalyse von Fluoro-Chloro-Bromo-Platinaten(IV) / Preparation, 19F and 195Pt NMR Spectra, Vibrational Spectra and Normal Coordinate Analysis of Fluoro-Chloro-Bromo-Platinates(IV)

By stereoselective ligand exchange reactions of [PtF5Cl]2− and cis-[PtF4Cl2]2− with Br− mixtures containing seven different fluoro-chloro-bromo- and two fluoro-bromo-platinates(IV) are formed, from which trans-Cs2[PtF4ClBr] 4t 11 and mer-Cs2[PtF3Clc 2Br] 3m2c 1 have been isolated by ion exchange chromatography on DEAE cellulose. All threefold mixed complexes could be detected by in situ 19F and 195 Pt NMR measurements. Due to the stronger trans influence of Cl in comparison with F on asymmetric F′-Pt-Cl′ axes the F atoms are deshielded and their signals δ(19F) are shifted on the average by 106 ppm to lower field as compared with δ(19F) of symmetric F-Pt-F axes. For the same reason the mean coupling constant 1J(FPt) of 1857 Hz is 44 % higher than 1J( FPt) of 1288 Hz. The substitution of a cis positioned Cl against Br causes shifts of -7,6 ppm for δ(19F) and of -8,4 ppm for δ(19F ). The cis influence on the coupling constants 1J(F P t) and 1J( FPt), on the average 4 Hz, is more than two orders of magnitude smaller than the trans influence. The coupling constants between inequivalent F atoms 2J(FF) amounts to 44 Hz. The mean highfield shift of the l95Pt signals on exchange of one F for Cl is 1177, of one Cl for Br 210 ppm. Due to the increasing trans influence F < Cl < Br on the stretching vibrations of asymmetrically coordinated axes characteristic frequency shifts of up to 15 % are observed. The normal coordinate analyses performed on 4t11 and 3m2c 1 reveal that the force constant fd(PtF) is by 15 % higher than fd(PtF), and that fd(PtCl′) is by 31 % higher than fd(PtCl). Very intense Raman bands at 277 and 267 cm −1 are explained by strong vibrational coupling of the π-deformation with a symmetric valence mode of the Cl -Pt-Br′axis.

The performance of B3-LYP density functional theory in describing S N2 reactions at saturated carbon

The performance of the B3-LYP variant of density functional theory when used in conjunction with the 6-31G(d) and 6-311 + G(3df, 2p) basis sets in describing the prototypical gas-phase S N2 reactions of Cl − + CH 3Cl and CH 3Br has been examined in detail. Reasonable values of the complexation energies ( ΔH comp) for the ion-molecule complexes formed in these reactions are obtained. However, the overall ( ΔH ovr #) and central ( ΔH cent #) barriers for these reactions calculated using the B3-LYP functional are significantly underestimated when compared with G2(+) or experimental results. This implies that the B3-LYP energies for the Cl(H 3C)Cl − (D 3h) and Cl(H 3C)Br − (C 3v) transition structures are relatively too low. The B3-LYP errors appear to be systematic, with similar errors being found for corresponding quantities for the two reactions examined.

Si-C-Bond cleavage in 1-organylsilatranes by bromine or iodine chloride

The Si-C bond in I-organylsilatranes is cleaved by bromine or iodine chloride to yield 1-bromo- or 1-chlorosilatrane respectively. In the presence of Et2O or THF and under the action of dioxane dibromide, I-halosilatrane

ChemInform Abstract: Effect of Pyridine on the Regio‐ and Stereochemistry in the Addition of Bromine Chloride to α,β‐Unsaturated Aldehydes and Ketones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.