- Mimicking the vanadium bromoperoxidases reactions: Mild and selective bromination of arenes and alkenes in a two-phase system
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Vanadium bromoperoxidases catalyze the oxidation of bromide ion by hydrogen peroxide to a bromine-equivalent intermediate. This, in turn, brominates organic molecules. The hypothesis is made that the former reaction takes place in the hydrophilic portion of the enzyme whereas the latter proceeds in a hydrophobic one in which the brominating intermediate is rapidly transferred. We have reproduced such situation by employing a two-phase (H2O/CHCl3) system. In the aqueous acid phase H2O2 and catalytic amounts of NH4VO3 are present, together with KBr. The substrates, i.e. aromatic hydrocarbons and alkenes are dissolved in CHCl3. The bromination proceeds smoothly with stirring, at 25°C, providing high yields of the corresponding brominated products.
- Conte,Di Furia,Moro
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- Stereoselectivity and Reversibility of Electrophilic Bromine Addition to Stilbenes in Chloroform: Influence of the Bromide-Tribromide-Pentabromide Equilibrium in the Counteranion of the Ionic Intermediates
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Two equilibria were found in chloroform solutions of Bu4N(1+)Br(1-) and Br2, leading to tribromide and pentabromide salts.The electronic spectra and formation constants of both (K3 = 2.77 (0.13) * 104 M-1 and K5
- Bianchini, Roberto,Chiappe, Cinzia
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- Stereoselective halogenations of alkenes and alkynes in ionic liquids
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(matrix presented) Room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium chloride, are used as "green" recyclabl
- Chiappe, Cinzia,Capraro, Dario,Conte, Valeria,Pieraccini, Daniela
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- Mild and Efficient Vicinal Dibromination of Olefins Mediated by Aqueous Ammonium Fluoride
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A mild and efficient vicinal dibromination of olefins has been developed by using saturated aqueous ammonium fluoride solution as the promoter. Inexpensive and commercially available N -bromosuccinimide (NBS) was used as the brominating reagent. The corresponding vicinal dibromoalkanes could be obtained in good to excellent yields.
- Ng, Wing Hin,Shing, Tony K. M.,Yeung, Ying-Yeung
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supporting information
p. 419 - 424
(2018/02/23)
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- Brominated methanes as photoresponsive molecular storage of elemental Br2
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The photochemical generation of elemental Br2 from brominated methanes is reported. Br2 was generated by the vaporization of carbon oxides and HBr through oxidative photodecomposition of brominated methanes under a 20 W low-pressure mercury lamp, wherein the amount and situations of Br2 generation were photochemically controllable. Liquid CH 2Br2 can be used not only as an organic solvent but also for the photoresponsive molecular storage of Br2, which is of great technical benefit in a variety of organic syntheses and in materials science. By taking advantage of the in situ generation of Br2 from the organic solvent itself, many organobromine compounds were synthesized in high practical yields with or without the addition of a catalyst. Herein, Br2 that was generated by the photodecomposition of CH2Br2 retained its reactivity in solution to undergo essentially the same reactions as those that were carried out with solutions of Br2 dissolved in CH 2Br2 that were prepared without photoirradiation. Furthermore, HBr, which was generated during the course of the photodecomposition of CH2Br2, was also available for the substitution of the OH group for the Br group and for the preparation of the HBr salts of amines. Furthermore, the photochemical generation of Br2 from CH2Br2 was available for the area-selective photochemical bleaching of natural colored plants, such as red rose petals, wherein Br2 that was generated photochemically from CH 2Br2 was painted onto the petal to cause radical oxidations of the chromophoric anthocyanin molecules. The generation of Br 2 from brominated methanes occurred upon photoirradiation under O2. The solutions that contained elemental Br2 were useful for the synthesis of organobromine compounds and the macroscopic photochemical bleaching of colored plants. Copyright
- Kawakami, Kazumitsu,Tsuda, Akihiko
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p. 2240 - 2252
(2012/11/06)
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- Verification of stereospecific dyotropic racemisation of enantiopure d and l-1,2-dibromo-1,2-diphenylethane in non-polar media
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The first example of a dyotropic rearrangement of an enantiomerically pure, conformationally unconstrained, vicinal dibromide confirms theoretical predictions: d and l-1,2-dibromo-1,2-diphenylethane racemise stereospecifically in refluxing benzene without crossover to the meso-isomer. An orbital analysis of this six-electron pericyclic process is presented.
- Christopher Braddock,Roy, Debjani,Lenoir, Dieter,Moore, Edward,Rzepa, Henry S.,Wu, Judy I-Chia,Von Rague Schleyer, Paul
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supporting information
p. 8943 - 8945
(2012/11/13)
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- Organocatalytic diastereoselective dibromination of alkenes
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A highly diastereoselective pyrrolidine-promoted dibromination of alkenes by combination of NBS and succinimide is presented. The pyrrolidine-mediated dibromination of alkenes is higly anti-selective and gives the corresponding products in moderate to high yields and up to >25:1 dr.
- Zhu, Mingzhao,Lin, Shuangzheng,Zhao, Gui-Ling,Sun, Junliang,Córdova, Armando
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experimental part
p. 2708 - 2712
(2010/07/04)
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- Selective aerobic oxidative dibromination of alkenes with aqueous HBr and sodium nitrite as a catalyst
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Various alkenes (internal, terminal, aryl and alkyl substituted) and 1,2-diphenylethyne were efficiently and selectively dibrominated using 2 equivalents of 48% aqueous hydrobromic acid, with air as an oxidant and sodium nitrite as a catalyst. Despite the presence of water, only trans dibromination occurred producing anti-1,2-dibromoalkanes and (E)-1,2-dibromo-1,2- diphenylethene. A comparison of resource demand, waste production and environmental, health and safety issues of the NaNO2 catalyzed aerobic bromination with molecular bromine and other oxidative bromination methods revealed that the proposed method is not only selective and effective but has a better environmental profile.
- Podgorsek, Ajda,Eissen, Marco,Fleckenstein, Jens,Stavber, Stojan,Zupan, Marko,Iskra, Jernej
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experimental part
p. 120 - 126
(2010/04/22)
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- The important role of solvent vapor in an organic solid state reaction
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Some organic reactions in the solid state proceeded very efficiently and selectively in the presence of a small amount of solvent vapor. The Royal Society of Chemistry 2005.
- Nakamatsu, Seiken,Toyota, Shinji,Jones, William,Toda, Fumio
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p. 3808 - 3810
(2007/10/03)
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- Solvolytic stereoselective debromination of vic-dibromides with HMPA
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A simple and efficient procedure for the debromination of vic-dibromides has been reported with hexamethylphosphoric triamide at 155-160°C under a nitrogen atmosphere without the aid of any reagent.
- Khurana,Bansal,Chauhan
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p. 1089 - 1091
(2007/10/03)
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- Radical bromination of 1,1- and 1,2-diphenylethylenes in 1,2-dichloroethane
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The radical bromination of 1,1- and 1,2-diphenylethylenes in 1,2-dichloroethane was investigated on the basis of kinetic and product distribution data. Whereas the ionic process followed a third-order rate law (second order in Br2), the radical
- Bellucci, Giuseppe,Chiappe, Cinzia
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p. 685 - 692
(2007/10/03)
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- Preassociation, free-ion, and ion-pair pathways in the electrophilic bromination of substituted cis- and trans-stilbenes in protic solvents
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Rates and products of electrophilic bromination of ring-substituted cis- and trans-stilbenes have been investigated in acetic acid, trifluoroethanol, ethanol, methanol, and water-methanol mixtures. The mY(Br) relationships (linear for nucleophilic solvent
- Ruasse, Marie-Fran?oise,Lo Moro, Giacomo,Galland, Bernard,Bianchini, Roberto,Chiappe, Cinzia,Bellucci, Giuseppe
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p. 12492 - 12502
(2007/10/03)
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- AFM ON CHEMICALLY REACTING CRYSTALS
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A review is given on recent developments of atomic force microscopic (AFM) studies on chemically reacting organic crystals.Three further basic phase transformation mechanisms have been added to the previous five.Both photodimerizations and gas/solid reactions are studied in detail by scanning the surfaces of initial and chemically reacted crystals of anthracenes, thiohydantoines, α- and β-cinnamic acid, and stilbene at different faces, where technically possible.The AFM-features are correlated to known crystal structure data with the aid of semiempirical calculations in part.Thus, detailed molecular mechanisms for the far-reaching well-directed transport phenomena may be derived in most cases and the appearance of the submicroscopic features rationalized.Unimolecular terrace steps of anthracene behave as independent crystal face already.The addition of bromine and chlorine leads to new solid phases directly even though there might be formed mixtures of stereoisomers.If a submicroscopic liquid phase is formed as in the reaction of α-cinnamic acid with chlorine, the surface will be remodelled by the tip and this provides for interesting nanostructures.In many cases there are secondary phase transformations apparently from one form of mixed crystals into another form of mixed crystals either upon continuation of irradiation or just on standing of gas/solid reacted crystals for several hours. - Keywords: atomic force microscopy, solid state photochemistry, gas/solid reaction, basic mechanism, phase transformation, molecular mechanism, unimolecular step, crystal face, crystal structure, nanostructures
- Kaupp, Gerd
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p. 153 - 170
(2007/10/02)
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- Dehalogenation of Vicinal Dibromides by Electrogenerated Polysulfide Ions in Dimethylacetamide
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Dehalogenation reactions of vic-dibromides by electrogenerated S62- (S3 anion radical), S42- or S32- polysulfide ions have been investigated in dimethylacetamide by use of spectroelectrochemistry on a series of dibromides: methyl erythro-2,3-dibromo-3-phenylpropanoate (1), diethyl meso-2,3-dibromosuccinate (2), meso-1,2-dibromo-1,2-diphenylethane (3), DL-1,2-dibromo-1,2-diphenylethane (4), 1,2-dibromobutane (5), 1,2-dibromophenylethane (6), DL-2,3-dibromobutane (7), erythro-3,4-dibromoheptane (8), threo-3,4-dibromoheptane (9), meso-5,6-dibromodecane (10), trans-1,2-dibromocyclohexane (11).Substitution and elimination are competing mechanism with 5-7 while the quantitative formation of alkenes is observed with the other substituted dibromides.In dilute solutions, indirect electrochemical reductions of vic-dibromides have been performed in the presence of small amounts of sulfur as catalyst at potentials leading to S(-1/3) ions with 1-3, or at more cathodic potentials (formation of S42-/S32- ions) for 8-11.On a preparative scale, stereospecific anti debrominations afford only E alkenes from chemical reaction with 3 or mediated electrolysis of 1,2 or 10.Kinetic studies of the reactions between S(-1/3) ions and compounds 4, 8-10 imply that the dianions S62- are the eliminating agents rather than S3 anion radical ions for the concerted anti dehalogenations.
- Bosser, Gerard,Paris, Jacky
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p. 2057 - 2063
(2007/10/02)
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- Bromination of Alkenes in Acetonitrile. A Rate and Product Study
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The reaction of simple alkenes and aryl alkenes with molecular bromine in damp MeCN occurred with solvent incorporation to give 2-bromo-1-(N-acetylamino)alkanes, 2-methyloxazolines, 2-acetoxyalkylamine hydrobromides, and 2-(N-acetylamino) alcohols.These products arose by the transformation of initially formed 2-bromo-1-(N-acetylamino)alkanes obtained by MeCN attack on bromonium or bromocarbonium ions to give nitrilium tribromide salts.These reacted with water to give 2-bromo-1-(N-acetylamino)alkanes.The kinetic profile of the reaction showed a very fast initial reaction of the alkene and Br2 to yield the nitrilium tribromide, followed by a much slower reaction of Br3(1-) with the alkene.The incorporation of MeCN was Markovnikov and stereospecifically anti.The degree to which incorporation of solvent occurred depended upon the alkene structure and the initial reagent concentrations.A rationalization for the observed chemoselectivity and its dependence on the reaction conditions is offered.
- Bellucci, Giuseppe,Bianchini, Roberto,Chiappe, Cinzia
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p. 3067 - 3073
(2007/10/02)
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- Different Reversibility of Bromonium vs β-Bromocarbonium Ions Formed during the Electrophilic Bromination of Substituted Stilbenes. Evidence for Rate Determination during the Product-Forming Step
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In order to check the relative reversibility of brominium and β-bromocarbonium ion formation, the product distributions of the reactions of Br2 with cis- and trans-stilbene (1b and 2b) and with their p-methyl (1a and 2a), p-(trifluoromethyl) (1c and 2c). and p,p′-bis(trifluoromethyl) derivatives (1d and 2d) in 1,2-dichloroethane have been determined in the 10-1-10-4 M concentration range. The rate constants (k3) for the bromination of these stilbenes at 25 °C spanned 7 orders of magnitude. The observed dibromide ratios showed that an open β-bromocarbonium ion was the intermediate of the bromination of 1a and 2a, whereas bridged or partially bridged ions were involved with all other olefins. In these cases, the extent of bridging increased, and equilibration to the more stable trans bromonium ion occurred at the lowest reagent concentrations to give the erythro (or meso) dibromide 3 as the main product. The increase in 3 was always accompanied by an increase in cis-trans olefin isomerization during the bromination of the cis olefin. This is attributed to a return of the trans bromonium ion to the corresponding olefin. This process was maximum with 1d, and minimum with 1a. It is concluded that, whereas the formation of the β-bromocarbonium ion intermediate is completely rate-determining in the case of 2a, both the formation of the trans bromonium ion and the following dibromide formation are partially rate-determining in the case of 2d.
- Bellucci, Giuseppe,Bianchini, Roberto,Chiappe, Cinzia,Brown, Robert Stanley,Slebocka-Tilk, Henryka
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p. 8012 - 8016
(2007/10/02)
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- Concentration Dependence of the Steric Course of the Bromine Addition to Arylalkenes. The Case of Stilbenes
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The ratios of meso- to d,l-1,2-dibromo-1,2-diphenylethane obtained in the bromination of cis- and trans-stilbene in 1,2-dichloroethane have been determined by HPLC as a function of the reagent concentrations.With stoichiometric reagents both reactions wer
- Belluci, Giuseppe,Bianchini, Roberto,Chiappe, Cinzia,Marioni, Franco
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p. 4094 - 4098
(2007/10/02)
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- Evidence for a Reversible Electrophilic Step in Olefin Bromination. The Case of Stilbenes
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Bromonium-bromide ion couple intermediates have been generated by reacting erythro- and threo-2-bromo-1,2-diphenylethanol with gaseous HBr in 1,2-dichloroethane and in chloroform.It has been shown that in both solvents these intermediates mainly collapse to meso-1,2-dibromo-1,2-diphenylethane but also release Br2 to give trans-stilbene.The ratios of trans-stilbene to the meso dibromide obtained in all these reactions ranged between 9:91 and 22:78.The product distributions of the additions of HBr and Br2, both in the absence and in the presence of HBr, have also been determined. cis-Stilbene rapidly added HBr in both solvents, but in 1,2-dichloroethane isomerization to trans-stilbene also occurred to a large extent. trans-Stilbene mainly underwent oligo- or polymerization.The reactions of both olefins with Br2 were found to be not stereospecific.In the presence of HBr, the bromination of trans-stilbene became anti stereospecific, but in the case of cis-stilbene it maintained only a very modest stereoselectivity, and in chloroform HBr addition was predominant.The kinetics of bromination of both trans- and cis-stilbene in 1,2-dichloroethane were shown to follow very cleanly a third-order rate law (second order in Br2).However, the product analysis during the bromination of cis-stilbene showed that significant amounts of the trans olefin were always present at incomplete conversion.It has been shown that the latter olefin is formed by Br2-catalyzed isomerization of the starting cis olefin.All these results can be rationalized by assuming that the formation of bromonium-bromide or bromonium-tribromide ion pair intermediates in the discussed reactions is actually reversible.
- Bellucci, Giuseppe,Chiappe, Cinzia,Marioni, Franco
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p. 515 - 522
(2007/10/02)
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- Organic Gas-Solid Reactions with Stilbenes, Chalcones, and Enamides
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Crystalline stilbene (1) adds gaseous chlorine and bromine without intermediate melting.The stereoselectivity is similar to that observed in solutions.Triphenylethene (3) also yields the products 4 in gas-solid reactions with chlorine and bromine, but these products tend to loose HX from the crystal; their conversion products are described.Neither crystalline 1 nor 3, but (E)-1,2-diphenyl-1-propene (7) adds gaseous hydrogen bromide regiospecifically.The same is true for the crystalline chalcone 10, which adds hydrogen bromide and -chloride selectively to give 11 nonisotypically.Gaseous ammonia reconverts crystalline 11 into 10.The enamide 12 in its crystalline state adds the gases hydrogen bromide, -chloride, methanethiol and hydrogen, to give the products 13, but also 15 (addition and condensation) and 16 (double addition). 13f which is formed via hydrogenation of crystals is not isotypical with its precursor 12.The liquid 17 crstallizes on freezing and then easily adds the gases hydrogen bromide (> - 50 deg C) and hydrogen chloride (> - 80 deg C) in highly controlled reactions to give the reactive compounds 18.These are converted not only into oligomers but also into the derivatives 19, 20, 21, and 22.The advantages of the unusual reaction procedures are discussed.
- Kaupp, Gerd,Matthies, Doris
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p. 1897 - 1904
(2007/10/02)
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