Molecular Bromine Research Articles

Synthesis and Halocyclization of 5-Allyl-2-benzyl(allyl)sulfanyl-6-methylpyrimidin-4(3H)-ones

Alkylation of 5-allyl-6-methyl-2-thiouracil with benzyl chloride and allyl bromide afforded 2-benzyl(allyl)sulfanyl-5-allyl-6-methylpyrimidin-4(3H)-ones. 5-Allyl-2-(benzylsmfanyl)-6-methylpyrirmdin-4(3H)-one reacted with molecular bromine and iodine to give substituted furo[2,3-d]pyrimidines. Depending on the conditions, the reaction of 5-allyl-2-(allylsulfanyl)-6-methylpyrimidin-4(3H)-one with iodine led to the formation of 6-allyl-3-(iodomethyl)-5-methyl-7-oxo-2,3,7,8-tetrahydro[1,3]thiazolo[3,2-a]pyrimidinium iodide or 3,7-bis(iodomethyl)-5-methyl-2,3,6,7-tetrahydrofuro[2,3-d][1,3]thiazolo[3,2-a]pyrimidinium iodide.

Solvent-free synthesis of molecular bromine and its application for in situ bromination of aromatic compounds

Solvent-free synthesis of molecular bromine and its application for in situ bromination of aromatic compounds

Synthesis of 30-Bromo- and 30-Azido-20-oxo-29-nor-3β,28-diacylbetulin Derivatives

Ozonolysis of 3β,28-diacyloxylup-20,29-enes gave 20-oxo-29-nor-3β,28-diacyloxylup-20,29-enes, which were brominated with molecular bromine in AcOH to obtain a mixture of 30-bromo- and 30-dibromo derivatives. Ozonolysis of 30-bromo-3β,28-diacylbetulin produced 29-nor-30-bromoketones, whose reaction with sodium azide afforded 29-nor-30-azidoketones of the lupane series.

Modeling the Sources and Chemistry of Polar Tropospheric Halogens (Cl, Br, and I) Using the CAM‐Chem Global Chemistry‐Climate Model

AbstractCurrent chemistry climate models do not include polar emissions and chemistry of halogens. This work presents the first implementation of an interactive polar module into the very short‐lived (VSL) halogen version of the Community Atmosphere Model with Chemistry (CAM‐Chem) model. The polar module includes photochemical release of molecular bromine, chlorine, and interhalogens from the sea‐ice surface, and brine diffusion of iodine biologically produced underneath and within porous sea‐ice. It also includes heterogeneous recycling of inorganic halogen reservoirs deposited over fresh sea‐ice surfaces and snow‐covered regions. The polar emission of chlorine, bromine, and iodine reach approximately 32, 250, and 39 Gg/year for Antarctica and 33, 271, and 4 Gg/year for the Arctic, respectively, with a marked seasonal cycle mainly driven by sunlight and sea‐ice coverage. Model results are validated against polar boundary layer measurements of ClO, BrO, and IO, and satellite BrO and IO columns. This validation includes satellite observations of IO over inner Antarctica for which an iodine “leapfrog” mechanism is proposed to transport active iodine from coastal source regions to the interior of the continent. The modeled chlorine and bromine polar sources represent up to 45% and 80% of the global biogenic VSLCl and VSLBr emissions, respectively, while the Antarctic sea‐ice iodine flux is ~10 times larger than that from the Southern Ocean. We present the first estimate of the contribution of polar halogen emissions to the global tropospheric halogen budget. CAM‐Chem includes now a complete representation of halogen sources and chemistry from pole‐to‐pole and from the Earth's surface up to the stratopause.

Direct detection of atmospheric atomic bromine leading to mercury and ozone depletion.

Bromine atoms play a central role in atmospheric reactive halogen chemistry, depleting ozone and elemental mercury, thereby enhancing deposition of toxic mercury, particularly in the Arctic near-surface troposphere. However, direct bromine atom measurements have been missing to date, due to the lack of analytical capability with sufficient sensitivity for ambient measurements. Here we present direct atmospheric bromine atom measurements, conducted in the springtime Arctic. Measured bromine atom levels reached 14 parts per trillion (ppt, pmol mol-1; 4.2 × 108 atoms per cm-3) and were up to 3-10 times higher than estimates using previous indirect measurements not considering the critical role of molecular bromine. Observed ozone and elemental mercury depletion rates are quantitatively explained by the measured bromine atoms, providing field validation of highly uncertain mercury chemistry. Following complete ozone depletion, elevated bromine concentrations are sustained by photochemical snowpack emissions of molecular bromine and nitrogen oxides, resulting in continued atmospheric mercury depletion. This study provides a breakthrough in quantitatively constraining bromine chemistry in the polar atmosphere, where this chemistry connects the rapidly changing surface to pollutant fate.

Ultrasound Assisted Solvent/Metal Free Synthesis of 3‐Sulfenylindoles Employing TBATB‐Grafted MCM‐48 as a suitable Heterogeneous Catalyst.

AbstractA one pot synthesis of 3‐sulfenylindoles in a solvent and metal free condition is reported here. The ultrasonic protocol markedly accelerates the reaction between substituted indoles and disulfides providing desired products in good to excellent yield. The ultrasonication produces local heating effect which is comparatively more advantageous than conventional heating. The method is catalyzed by TBATB impregnated MCM‐48 which is as a selective and efficient heterogeneous catalyst, also a source of molecular bromine which in presence of DMSO leads to C−S coupling. The salient feature of this protocol is easy recovery and reusability of the catalyst up to minimum five consecutive cycles. The easy and clean operation, short reaction time and high yield of desired outcomes make this method a practically applicable one.

Single-Step Dual Functionalization: One-Pot Bromination-Cross-Dehydrogenative Esterification of Hydroxy Benzaldehydes with CCl3Br – A Comparison with Selectfluor

Bromination of phenolic compounds without directly using molecular bromine possesses much importance. In this article an IrIII/CCl3Br-assisted single-step double functionalization of hydroxy benzaldehydes is reported. It involves simultaneous esterification of the aldehyde group and bromination of the aryl ring of phenolic aldehydes in one-pot. The reaction proceeds under mild conditions in the presence of 445 nm blue LED light to obtain highly functionalized bromo hydroxy benzoates in moderate to good yields. In comparison, Selectfluor as an oxidant gives only non-bromo phenolic esters.

Electrophilic Bromination in Flow: A Safe and Sustainable Alternative to the Use of Molecular Bromine in Batch.

Bromination reactions are crucial in today’s chemical industry since the versatility of the formed organobromides makes them suitable building blocks for numerous syntheses. However, the use of the toxic and highly reactive molecular bromine (Br2) makes these brominations very challenging and hazardous. We describe here a safe and straightforward protocol for bromination in continuous flow. The hazardous Br2 or KOBr is generated in situ by reacting an oxidant (NaOCl) with HBr or KBr, respectively, which is directly coupled to the bromination reaction and a quench of residual bromine. This protocol was demonstrated by polybrominating both alkenes and aromatic substrates in a wide variety of solvents, with yields ranging from 78% to 99%. The protocol can easily be adapted for the bromination of other substrates in an academic and industrial environment.

ClNO2 Production from N2O5 Uptake on Saline Playa Dusts: New Insights into Potential Inland Sources of ClNO2.

Nitryl chloride (ClNO2), formed when dinitrogen pentoxide (N2O5) reacts with chloride-containing aerosol, photolyzes to produce chlorine radicals that facilitate the formation of tropospheric ozone. ClNO2 has been measured in continental areas; however, the sources of particulate chloride required to form ClNO2 in inland regions remain unclear. Dust emitted from saline playas (e.g., dried lakebeds) contains salts that can potentially form ClNO2 in inland regions. Here, we present the first laboratory measurements demonstrating the production of ClNO2 from playa dusts. N2O5 reactive uptake coefficients (γN2O5) ranged from ∼10-3 to 10-1 and ClNO2 yields (φClNO2) were >50% for all playas tested except one. In general, as the soluble ion fraction of playa dusts increases, γN2O5 decreases and φClNO2 increases. We attribute this finding to a transition from aerosol surfaces dominated by silicates that react efficiently with N2O5 and produce little ClNO2 to aerosols that behave like deliquesced chloride-containing salts that generate high yields of ClNO2. Molecular bromine (Br2) and nitryl bromide (BrNO2) were also detected, highlighting that playas facilitate the heterogeneous production of brominated compounds. Our results suggest that parameterizations and models should be updated to include playas as an inland source of aerosol chloride capable of efficiently generating ClNO2.

PH-dependent production of molecular chlorine, bromine, and iodine from frozen saline surfaces

Abstract. The mechanisms of molecular halogen production from frozen saline surfaces remain incompletely understood, limiting our ability to predict atmospheric oxidation and composition in polar regions. In this laboratory study, condensed-phase hydroxyl radicals (OH) were photochemically generated in frozen saltwater solutions that mimicked the ionic composition of ocean water. These hydroxyl radicals were found to oxidize Cl−, Br−, and I−, leading to the release of Cl2, Br2, I2, and IBr. At moderately acidic pH (buffered between 4.5 and 4.8), irradiation of ice containing OH precursors (either of hydrogen peroxide or nitrite ion) produced elevated amounts of I2. Subsequent addition of O3 produced additional I2, as well as small amounts of Br2. At lower pH (1.7–2.2) and in the presence of an OH precursor, rapid dark conversion of I− to I2 occurred from reactions with hydrogen peroxide or nitrite, followed by substantial photochemical production of Br2 upon irradiation. Exposure to O3 under these low pH conditions also increased production of Br2 and I2; this likely results from direct O3 reactions with halides, as well as the production of gas-phase HOBr and HOI that subsequently diffuse to frozen solution to react with Br− and I−. Photochemical production of Cl2 was only observed when the irradiated sample was composed of high-purity NaCl and hydrogen peroxide (acting as the OH precursor) at pH = 1.8. Though condensed-phase OH was shown to produce Cl2 in this study, kinetics calculations suggest that heterogeneous recycling chemistry may be equally or more important for Cl2 production in the Arctic atmosphere. The condensed-phase OH-mediated halogen production mechanisms demonstrated here are consistent with those proposed from recent Arctic field observations of molecular halogen production from snowpacks. These reactions, even if slow, may be important for providing seed halogens to the Arctic atmosphere. Our results suggest the observed molecular halogen products are dependent on the relative concentrations of halides at the ice surface, as we only observe what diffuses to the air–surface interface.

Functiaonalization of 2-(1-Cyclohexen-1-yl)aniline Derivatives

The reaction of 2-(1-cyclohexen-1-yl)aniline and -6-methylaniline with phthalic anhydride has afforded 2-(2-cyclohex-1-en-1-ylphenyl)- and 2-(2-cyclohex-1-en-1-ylphenyl)-6-methylphenyl)-1H-isoindole-1,3(2H)-diones. The reaction of the obtained isoindole-1,3-diones with bromine in dichloromethane in the presence of sodium bicarbonate has led to the formation of the product of pseudo-allylic halogenation. Replacement of the halogen atom by methoxy group has been performed by keeping 2-[2-(6-bromocyclohex-1-en-1-ylphenyl)-6-methylphenyl)]-1H-isoindole-1,3(2H)-dione in a methanolic solution in the presence of NaHCO3. The reaction of 2-(2-cyclohex-1-en-1-yl-6-methylphenyl)-1H-isoindole-1,3(2H)-dione with molecular bromine in the presence of methanol has given a co-halogenation product, whereas the dibromination product has been obtained in the presence of octyl alcohol.

Preparation of a novel bromine complex and its application in organic synthesis

Although molecular bromine (Br2) is a useful brominating reagent, it is not easy to handle. Herein, we describe the preparation of a novel air-stable bromine complex prepared from 1,3-dimethyl-2-imidazolidinone (DMI) and Br2, which was identified to be (DMI)2HBr3 by spectral and X-ray techniques. This complex was then used to brominate olefins, carbonyl compounds, and aromatics, as well as in the Hofmann rearrangement. Yields of reaction products using this complex were almost the same or superior to those using other bromine alternatives.

Long-term ambient air-stable cubic CsPbBr3 perovskite quantum dots using molecular bromine.

We report unprecedented phase stability of cubic CsPbBr3 quantum dots in ambient air obtained by using Br2 as halide precursor. Mechanistic investigation reveals the decisive role of temperature-controlled in situ generated, oleylammonium halide species from molecular halogen and amine for the long term stability and emission tunability of CsPbX3 (X = Br, I) nanocrystals.

Sulphide as a leaving group: highly stereoselective bromination of alkyl phenyl sulphides.

A conceptionally novel nucleophilic substitution approach to synthetically important alkyl bromides is presented. Using molecular bromine (Br2), readily available secondary benzyl and tertiary alkyl phenyl sulphides are converted into the corresponding bromides under exceptionally mild, acid- and base-free reaction conditions. This simple transformation allows the isolation of elimination sensitive benzylic β-bromo carbonyl and nitrile compounds in mostly high yields and purities. Remarkably, protic functionalities such as acids and alcohols are tolerated. Enantioenriched benzylic β-sulphido esters, readily prepared by asymmetric sulpha-Michael addition, produce the corresponding inverted bromides with high stereoselectivities, approaching complete enantiospecificity at -40 °C. Significantly, the reported benzylic β-bromo esters can be stored without racemisation for prolonged periods at -20 °C. Their synthetic potential was demonstrated by the one-pot preparation of γ-azido alcohol (S)-5 in 90% ee. NMR studies revealed an initial formation of a sulphide bromine adduct, which in turn is in equilibrium with a postulated dibromosulphurane intermediate that undergoes C-Br bond formation.

Bromate Reaction on a Rotating Disc Electrode: A New Method of Obtaining Approximate Analytical Solutions for Stationary Regime

A new method (AA approximation) is proposed for obtaining approximate analytical solutions of a system of equations describing the transport of the basic reagents for the electroreduction process of the BrO $$_{3}^{ - }$$ anion on a rotating disc electrode in an acid medium in the presence of very small additions of molecular bromine. This process is of significant interest both from the fundamental point of view (as an example of a new electrochemical EC'' mechanism with autocatalytic properties) and from the applied point of view in the context of prospects to create, on its basis, innovation power sources—bromate redox flow batteries. Since the previously proposed method for solving the system of kinetic transport equations for this system turned out to be inapplicable for very large diffusion layer thicknesses and very strong currents, here a new method of obtaining approximate analytical expressions for concentration profiles and maximum current is proposed. It has been shown that its predictions are in good agreement with the results of the numerical solution of the same problem in a wide range of system parameters, including the region of very large diffusion layer thicknesses, which confirms the validity of the used analytical approximations.

Evolution of Anolyte Composition in the Oxidative Electrolysis of Sodium Bromide in a Sulfuric Acid Medium

The oxidation of a 10 mM aqueous solution of sodium bromide in a sulfuric acid medium on the surface of a platinum electrode in a cell with separated spaces was studied. The process is important in view of the use of the bromine–bromide redox couple in redox flow batteries. The study was performed by cyclic voltammetry, potentiostatic chronoamperometry with optical absorption spectrum recording, and measurements of the potential of the redox reference electrode. A numerical procedure for processing the experimental spectra of the solution was developed to separate them into the spectrum of molecular bromine and the residual signal. The latter was attributed to the absorption of the tribromide anion based on the literature data. The experimental dependences of the Br2 and Br3- concentrations for the oxidative electrolysis of the NaBr solution in the sulfuric acid medium agreed well with the theoretical predictions. The current efficiency of bromine formation was evaluated.

Graphene Oxide Promoted Oxidative Bromination of Anilines and Phenols in Water.

The mildly acidic and oxidative nature of graphene oxide, with its large surface area available for catalytic activity, has been explored in aromatic nuclear bromination chemistry for the first time. The versatile catalytic activity of graphene oxide (GO) has been used to selectively and rapidly brominate anilines and phenols in water. The best results were obtained at ambient temperatures using molecular bromine in a protocol promoted by oxidative bromination catalyzed by GO; these transformations proceeded with 100% atom economy with respect to bromine and high selectivities for the tribromoanilines and -phenols. Reduced graphene oxide (r-GO) was observed to form after the second recycle (third use) of GO. This technique is also effective with N-bromosuccinimide (NBS) as the brominating reagent. In the case of NBS, reactions were instantaneous and the GO displayed excellent recyclability without any loss of activity over several cycles.

Mechanism of CF3Br Photolysis at the Wavelength of 253.7 nm

The kinetics of the photolysis of CF3Br (Halon 1301) at various durations of irradiation of CF3Br−oxygen mixtures at a wavelength of 253.7 nm is studied. The spectra and absorbances of the reactants are obtained within the range of 200−900 nm using an M-40 spectrophotometer. Kinetic data are determined from a change in the absorption spectra at a wavelength of 416 nm, which corresponds to the maximum absorption of molecular bromine. A kinetic mechanism of CF3Br photolysis is proposed, and the quantum yield and the absorption cross section of CF3Br at this wavelength are determined.

Kinetics Study of Heterogeneous Bromine Release from the Reaction between Gaseous Ozone and Aqueous Bromide Solution.

The heterogeneous release of molecular bromine, Br2, from the reaction between gaseous ozone and aqueous bromide ion in seawater ice and sea salt aerosols is considered to be an initial source of reactive bromine species in the troposphere. Recent studies have demonstrated that the uptake of ozone by aqueous bromide solution is promoted by reactions at the gas-liquid interface. The present work investigated the heterogeneous reaction between gaseous ozone and aqueous bromide solution at atmospheric pressure and room temperature using a wetted wall flow reactor combined with a chemical ionization mass spectrometer. The emission rate of Br2 was measured as a function of gaseous ozone concentration, aqueous bromide concentration, and pH. In addition, we conducted a simple kinetics model simulation that included only bulk aqueous-phase reactions and compared the theoretical values with the experimentally determined values. The Br2 emission rates measured experimentally differ from the simulated rates at relatively high bromide concentration, as well as in the pH region of 6-9. These differences might be explained by different Br- concentration and/or deprotonation efficiency near the interface region and those in the bulk solution.

NaBr mediated regioselective synthesis of 3-Selanylindoles

GRAPHICAL ABSTRACT