Dibromomethane Research Articles

The relationship between volatile halocarbons and phytoplankton pigments during a Trichodesmium bloom in the coastal eastern Arabian Sea

Eukaryotic phytoplankton such as diatoms and prymnesiophytes produce biogenic halocarbons in the ocean that serve as important sources of chlorine and bromine to the atmosphere, but the role of cyanobacteria in halocarbon production is not well established. We studied distributions of chloroform (CHCl 3), carbon tetrachloride (CCl 4), methylene bromide (CH 2Br 2) and bromoform (CHBr 3) in relation to phytoplankton composition, determined from pigment analysis complemented by microscopic examination, for one month in coastal waters of the eastern Arabian that experienced a Trichodesmium bloom that typically occurs during the Spring Intermonsoon season. High concentrations of zeaxanthin (23 μg l −1), alpha beta betacarotene (6 μg l −1) and chlorophyll a (67 μg l −1) were found within the bloom whereas the marker pigment concentrations were low outside the bloom. CHCl 3 and CCl 4 occurred in relatively high concentrations in surface waters whereas CH 2Br 2 and CHBr 3 were restricted to the subsurface layer. Chlorinated halocarbons were positively inter-correlated and with CHBr 3. The observed spatial and temporal trends in brominated compounds appear to be related to the abundance of Trichodesmium although correlations between concentrations of brominated compounds with various marker pigments were poor and statistically non-significant. The results support the existence of multiple sources and sinks of halogenated compounds, which might obscure the relationship between halocarbons and phytoplankton composition.

Methylene bromide chemistry and photochemistry on rutile TiO 2(110)

The chemistry and photochemistry of methylene bromide (CD 2Br 2) on the rutile TiO 2(110) surface was probed using temperature programmed desorption (TPD). CD 2Br 2 desorbed in three desorption states at 145, 160 and 250 K tentatively assigned to desorption from the multilayer, from an η 1-CD 2Br 2 species and a bridging η 2-CD 2Br 2 species, respectively. The latter two TPD states presumably involve binding of CD 2Br 2 molecules to the surface through Br coordination at five-coordinate Ti 4+ surface sites. The 160 and 250 K TPD states saturated at coverages of 1.0 and 0.33 ML, respectively, where 1 ML is equivalent to the surface Ti 4+ site density (5.2 × 10 14 cm − 2 ). No thermal decomposition of CD 2Br 2 was observed on either the clean surface or with preadsorbed O 2. UV irradiation of CD 2Br 2 on TiO 2(110) resulted in predominately photodesorption, with trace amounts of photodecomposition evidenced in TPD. The rate of CD 2Br 2 photodesorption from TiO 2(110) occurred with a low cross section (~ 2 × 10 − 21 cm 2) similar to that expected from direct optical excitation of CD 2Br 2. This observation suggests that charge carriers generated in TiO 2(110) were no more effective in activating adsorbed CD 2Br 2 molecules than would be expected through direct molecular excitation. These findings suggest that photocatalytic destruction of halocarbons such as CD 2Br 2 on TiO 2 may preferentially occur though indirect processes (such as OH radical attack) as opposed to direct electron transfer processes involving charge carriers generated in TiO 2 by bandgap excitation.

Development of New N,N-Ligands for the Enantioselective Copper(II)-Catalyzed Henry Reaction

This account shows our efforts towards the development of new N, N-ligandsand their application in the asymmetric Henry reaction. Iminopyridineligands were prepared by the condensation of chiral monoterpeneketones and pyridinylalkylamines. The complexes of these ligandswith copper(II) ions catalyzed the enantio-selective additionof nitromethane to aldehydes with generally high yields and moderateenantioselectivities. The same reaction with other nitroalkanesgave racemic products. Stereoselective reduction of the imino groupallowed us to obtain new aminopyridine ligands. The new ligandswere shown to be more efficient, and they catalyzed the additionof nitromethane and also larger nitroalkanes to aldehydes to givethe corresponding products in generally very high yields and excellentenantiomeric excesses. We have used this aminopyridine catalyticsystem in the first catalytic enantioselective Henry reactions withbromo(nitro)methane and methyl 4-nitrobutanoate. The reaction involvingthe latter substrate gave multifunctional chiral building blocksthat were transformed into γ-lactams and δ-lactones.The application of the reaction to the synthesis of known amino(aryl)ethanolpharmaceuticals is also reported. Im-inopyridine ligands,however, were more efficient in the addition of nitromethane to α-ketoesters. 1 Introduction 1.1 Enantioselective Copper(II)-Catalyzed Henry Reaction 2 Enantioselective Henry Reaction with Aldehydes Catalyzed byCopper(II)-Iminopyridine Complexes 2.1 Design and Synthesis of Iminopyridine Ligands 2.2 Enantioselective Addition of Nitromethane to Aldehydes 2.3 Stereochemical Models 3 Enantioselective Henry Reaction with Aldehydes Catalyzed byCopper(II)-Aminopyridine Complexes 3.1 Design and Synthesis of Aminopyridine Ligands 3.2 Enantioselective Addition of Nitroalkanes to Aldehydes 3.3 Enantioselective Addition of Bromo(nitro)methane to -Aldehydes 3.4 Enantioselective Addition of Methyl 4-nitrobutanoate to Aldehydes 3.5 Synthesis of Chiral Amino(aryl)ethanol Derivatives 4 Enantioselective Henry Reaction with α-Keto Esters 5 Conclusion

“One-Pot” Multicomponent Approach to Indolizines and Pyrido[1,2-a]indoles

A new synthetic protocol for efficient and regiospecifc assembly of indolizines and pyrido[1,2-a]indoles by coupling of substituted methyl bromides and alkynes with corresponding pyrrole-2-carboxaldehyde and 1H-indole-2-carboxaldehyde has been developed. Additionally, a possible mechanism for the reaction is proposed.

High-resolution spectroscopy of the ν8 band of methylene bromide using a quantum cascade laser

A continuous wave cavity ringdown spectrometer with a Fabry-Perot quantum cascade laser has been used to collect a rotationally-resolved infrared spectrum of the ν 8 vibrational band of methylene bromide in a slit nozzle expansion. In our laboratory, previous observations of the vibrational band were limited by spectral coverage to only the P and Q-branches and by the 24 MHz step-size of the laser [1]. The issue of limited spectral coverage has been resolved using a Fresnel rhomb and a wire grid polarizer to protect the laser from the destabilizing effects of back-reflection from the ringdown cavity. The frequency step-size of the spectrometer has been reduced from 24 MHz to 2 MHz. With both of these instrument enhancements, we have been able to record the R-branch of the vibrational band, and can resolve many lines that were previously blended in spectra acquired using a pinhole expansion nozzle. Significant hyperfine splitting was observed for the low- J transitions in the P and R-branches. It was possible to neglect the effects of hyperfine splitting for transitions involving J″ > 2 in the spectral assignment, and simulations using the constants obtained by fitting to Watson’s S-reduced Hamiltonian for CH 2 79Br 81Br, and the A-reduced form for CH 2 79Br 2 and CH 2 81Br 2, provide a good match to experimental spectra. A total of 297 transitions have been assigned for all three isotopologues, with a standard deviation of 0.00024 cm −1(∼7 MHz).

Experimental induction of larval metamorphosis by a naturally-produced halogenated compound (dibromomethane) in the invasive mollusc Crepidula fornicata (L.)

In many marine benthic invertebrates, the larval stage is the main vector of dispersal. Selective metamorphosis of larvae into an appropriate habitat is then essential to the survival of the benthic adult, with profound implications for population dynamics. Within this context, the identification of causal external factors triggering larval metamorphosis is of primary interest. In the widely invasive marine species Crepidula fornicata (L.), adult conditioned seawater is an effective inducer but the inducer has not yet been chemically characterized. In the present study, we experimentally tested the inductive ability of dibromomethane (DBM), a halogenated compound naturally-produced by red algae of the family Corallinaceae that co-occur with C. fornicata in the field. Through a series of three experiments, we demonstrated that DBM effectively induces metamorphosis of C. fornicata larvae, with a strong dose–response effect. Positive responses were observed for the four tested concentrations (5, 50, 500 and 5000 ppm), 5000 ppm being the most effective at inducing rapid metamorphosis. At this concentration, larvae became responsive at least five days before they became responsive to excess KCl, a chemical commonly used to test for competence in C. fornicata. Whether DBM could be an effective natural inducer would require further studies to quantify DBM and other halogenated compounds in the vicinity of C. fornicata beds, where they could influence larval behaviour even in the absence of other settlement cues.

Partial radial distribution functions of methylene halide molecular liquids

The total scattering structure factors of liquid methylene chloride (CH 2Cl 2), methylene bromide (CH 2Br 2) and methylene iodide (CH 2I 2) have been determined at room temperature and atmospheric pressure by neutron and X-ray diffraction. Experimental data were interpreted by means of the Reverse Monte Carlo structural modelling technique, which provided large particle configurations that were consistent with the measured structure factors. From the models, partial radial distribution functions were calculated directly. Comparison with hard sphere like reference systems showed that a surprisingly large part of the pair correlations can be captured via the simple concept of steric effects (packing fraction and molecular shape).

Excess molar enthalpies of dibromomethane with acetonitrile, furan and acetophenone at 303.15K

Abstract Excess molar enthalpies HE at 303.15 K using a microcalorimeter have been determined for binary liquid mixtures of dibromomethane (DBM) with acetonitrile, furan and acetophenone over the entire composition range. The excess molar enthalpies values are endothermic for DBM + acetonitrile, and +furan but they are exothermic for the system DBM + acetophenone. The observed values are fitted with the Redlich–Kister equation by means of the least squares method. The excess partial molar enthalpies of the components H m , 1 E and H m , 2 E have also been evaluated with the help of HE values. The results indicate the existence of specific interactions between all these components.

Excess Molar Enthalpies of Dibromomethane with Benzene, Methanol, Dimethylsulfoxide, and Pyrrolidin-2-one at 303.15 K

Excess molar enthalpies at 303.15 K have been determined for dibromomethane (DBM) with benzene, methanol, dimethylsulfoxide, and pyrrolidin-2-one. The excess molar enthalpies for DBM + benzene and + methanol are endothermic whereas exothermic for the system DBM + dimethylsulfoxide and + pyrrolidin-2-one. These results indicate the existence of specific interactions of DBM with all these compounds.

Inhibitory function of nitric oxide on the onset of metamorphosis in competent larvae of Crepidula fornicata: A transcriptional perspective

In diverse invertebrate species characterized by a biphasic life cycle, metamorphosis represents a fundamental biological transition which determines the fate of benthic population dynamics through settlement and recruitment. Within this context, nitric oxide (NO) is thought to act as an endogenous inhibitor of metamorphosis. While attention has been focused on the mechanisms of this inhibitory pathway with pharmacological agents and immunohistochemistry tools, relatively few studies have investigated transcriptional process at the origin of NO synthesis. In this paper, we report the isolation of a 218-bp cDNA fragment of an ortholog of the neuronal nitric oxide synthase ( nNOS) gene in the invasive marine species Crepidula fornicata. By the use of quantitative real-time PCR, we examine the transcription of this gene throughout larval development and in response to two inducers [K+ excess (20 mM), dibromomethane (DBM) (1000 ppm)] that are known to potentiate metamorphosis in invertebrate species. The level of transcription increased constantly during the larval development, suggesting an increased repressive effect over metamorphosis as larvae aged. Interestingly, maximum values were reached 6 h post-treatment, before declining within 20 h for all the tested conditions. Overall, our results are in agreement with the involvement, at a molecular level, of the NO signalling pathway in metamorphosis. The decrease in nNOS gene transcription post-induction could support the inhibitory effect of NO upon the onset of metamorphosis in competent larvae, although further studies are needed to fully describe the pathways triggered by K+ ions and DBM induction. Furthermore, results indicate that metamorphosis could occur after termination of endogenous inhibition, bringing support to the hypothesis of spontaneous metamorphosis.

Poly(4-vinylpyridine) catalyzed selective methanolysis of methyl and methylene bromides

The effect of poly(4-vinylpyridine) (PVP) on the methanolysis of methyl bromide and methylene bromide was studied at temperatures between 75 °C and 125 °C. PVP acts as an efficient HBr scavenger promoting the formation of dimethyl ether (DME) and dimethoxymethane (DMM) from the corresponding bromomethanes and methanol in moderate yields with high selectivity. No reaction was observed in the absence of PVP under the conditions adopted. The activity of the catalyst remained unchanged even after five cycles showing the efficacy and application of the polymer as an environmentally green reagent as well as catalyst in this methanolysis reaction.

A novel dichloromethane-degrading Lysinibacillus sphaericus strain wh22 and its degradative plasmid

Dichloromethane (DCM)-degrading bacterium strain wh22 (GenBank accession number FJ418643) was isolated and identified as Lysinibacillus sphaericus based on standard morphological and physiological properties, cellular fatty acid composition, mole percent guanine-cytosine content, and nucleotide sequence analysis of enzymatically amplified 16S ribosomal deoxyribonucleic acid. The strain also grew on many other halocarbons found in the waste gases of industrial effluents, such as 1,2-dichloroethane, chlorobromomethane, methylene bromide, 1,1,1-trichloroethane, trichloroethylene, and hexachlorobenzene. The strain harbored a novel degradative plasmid, pRC11 (48.8 kb). The genes coding for the metabolism of DCM were found to be plasmid-borne, and a physical map of the plasmid has been established. The purified plasmid was transformed to dcm- Escherichia coli DH5 at a rate of 1.65 x 10(5). The transformed cells were able to grow on DCM at a concentration of 5-16 mM and can be further used as an excellent source for genetic manipulations leading to the construction of genetically modified microbial strains or genetically engineered microorganisms.

A Versatile Synthesis of Annulated Carbazole Analogs Involving a Domino Reaction of Bromomethylindoles with Arenes/Heteroarenes

AbstractA ZnBr2‐mediated arylation of aryl/heteroaryl methyl bromides with arenes at 80 °C led to the formation of arylated products, which underwent subsequent 1,5‐sigmatropic rearrangement followed by electrocyclization and aromatization with loss of a diethylmalonate unit to afford the corresponding annulated products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

One case of occupational acute bromomethane poisoning

One case of occupational acute bromomethane poisoning

Kinetic and mechanistic examinations of reductive transformation pathways of brominated methanes with nano-scale Fe and Ni/Fe particles

In this study, carbon tetrabromide (CTB), bromoform (BF) and dibromomethane (DBM) were the target compounds investigated for their reduction kinetics and pathways with nano-scale Fe and Ni/Fe particles synthesized in laboratory. The BET surface areas of these nano-scale particles were around two orders of magnitude higher than that of the commercial micro-scale Fe particles. Batch reduction experiments were carried out with a metal loading of 2.5 g l −1 for the nano-scale particles, and 125 g l −1 for the commercial micro-scale Fe. The nano-scale Ni/Fe was the most reactive for reductive dehalogenation of the brominated methanes. The rates of bromide ion liberated during the reduction of the brominated methanes were usually higher than the disappearance rates of the parent compounds, indicating occurrence of concerted debromination mechanism. Analysis of the reduction kinetics showed that CTB and BF were mainly reduced through hydrogenolysis reaction, while over 76% of DBM was reduced through concerted reductive debromination to methane. Addition of Ni to Fe increased the specific reduction rates of the target compounds and reactive intermediates, but only marginally changed the distribution of their end products. Through comprehensive kinetic and mechanistic examinations of the reduction dehalogenation of various brominated methanes, a scheme summarizing their overall reduction pathways with the nano-scale Fe and Ni/Fe is proposed.

Phase Transfer Catalysis of Synthesizing Dialkoxymethane at Low Alkaline Concentration

The phase transfer catalyzed reaction of 2,4,6-tribromophenol and dibromomethane to synthesize α-bromomethyl 2,4,6-tribromophenyl ether and di-(2,4,6-tribromophenoxide) methane by quaternary ammonium salt was carried out in an alkaline solution of low KOH content/dibromomethane two-phase medium. Dibromomethane acts both as the organicphase reactant and the organic solvent; thus, no extra organic solvent is required. A large conversion of 2,4,6-tribromophenol is obtained at a region of low KOH content. During the reaction, two products, i.e., the mono-substituted product (α-bromomethyl 2,4,6-tribromophenyl ether) and the bi-substituted product (di-(2,4,6-tribromophenoxide)methane) were detected. In the reaction, the active catalyst (tetrabutylammonium 2,4,6-tribromophenoxide, ArOQ), which was produced from the reaction of 2,4,6-tribromophenol, potassium hydroxide and tetrabutylammonium bromide (TBAB or QBr), is purified as the crystalline product from the reaction solution. Based on the experimental data, a kinetic model is developed to describe the behaviors of the two organic-phase reactions. The two intrinsic rate constants of the two organic-phase reactions are determined. Effects of the reaction conditions, such as: agitation speed, amount of water, amount of TBAB catalyst, amount of dibromomethane, catalysts, temperature and inorganic salt KBr, on the conversion and the reaction rate are investigated in detail.

Synthesis of an asymmetric fullerene dimer via sequential cycloadditions

A single isomer of a monofunctionalised C 70 fullerene is isolated and characterised using variable temperature NMR spectroscopy. Pendant methylene bromide groups allow for further cycloaddition reactions and a C 60–C 70 asymmetric fullerene dimer is thus prepared.

Alkylation of tertiary arsines with methylene bromide and subsequent anion exchange

Tertiary arsines react with methylene bromide to give (bromomethyl)trialkyl(aryl)arsonium bromides. Treatment of the latter with magnesium perchlorate in aqueous ethanol solutions leads to anion exchange forming the corresponding tertiary arsonium perchlorates in nearly quantitative yields.

Synthesis and optical properties of azobenzene-containing poly(1-alkyne)s with different spacer lengths and ring substituents

Poly(1-alkyne)s containing azobenzene pendants with different spacer lengths and ring substitutents –{HC C[(CH 2) m COO–C 6H 4–N N–C 6H 4–NO 2]} n – P 1( m) m=3, 8 and –{HC C[(CH 2) m COO–C 6H 3- o-Br–N N–C 6H 4–NO 2]} n – P 2( m) m=3, 8} are designed and synthesized. The polymers are prepared in satisfactory yields with high molecular weights ( M w up to 3.3×10 4 Da) by [Rh(nbd)Cl] 2–Et 3N in THF or dioxane. Their structures and properties are characterized and evaluated by IR, UV, NMR, TGA, nonlinear optical and optical limiting analyses. All the polymers are completely soluble in common organic solvents and lose 5% of their weights at temperatures of ∼270 °C. The spacer length and the pendant substitutent affect the nonlinear optical and optical limiting properties of the polymers, with 1(3) showing superior properties than its counterparts 1(8) and 2(3) with long methylene spacers and bromide substitutents on the azobenzene pendants, respectively.

A Novel Method for the Synthesis of Dichloroalkenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.