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Bromine Atom (bromine + atom)
Selected AbstractsInternal Delivery of Soft Chlorine and Bromine Atoms: Stereoselective Synthesis of (E)-,-Halogenovinyl(aryl)-,3 -iodanes Through Domino ,3 -Iodanation,1,4-Halogen Shift,Fluorination of Alkynes.CHEMINFORM, Issue 51 2007Masahito Ochiai Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2006Yan Shi Abstract A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4-(2-bromo-2-methylpropionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br-TEMPO), was synthesized by the reaction of 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2-bromo-2-methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br-TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ,-end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468,2475, 2006 [source] Derivatisation for liquid chromatography/electrospray mass spectrometry: synthesis of pyridinium compounds and their amine and carboxylic acid derivativesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2003Samantha J. Barry A simple method has been developed for the pre-column derivatisation of low molecular weight primary and secondary amines and carboxylic acids using quaternary nitrogen compounds to enhance their detection by liquid chromatography/electrospray ionisation mass spectrometry (LC/ESI-MS). The synthesis of seven novel quaternary nitrogen reagents is described. The derivatives are designed to be relatively small molecules to avoid some of the steric hindrance problems that may be associated with larger derivatisation reagents. The compounds have amine and carboxylic acid functional groups with which to derivatise carboxylic acids and amines, respectively. Two of the compounds contain a bromine atom in order to assess the advantages of a bromine isotope pattern in the mass spectra. This acts as a simple marker for derivatisation and enables data processing by cluster analysis. Activation of the carboxylic acid group was achieved by the use of either 1-chloro-4-methylpyridinium iodide (CMPI) or the more reactive 1-fluoro-4-methylpyridinium p -toluenesulphonate (FMP).1 Using both of these active reagents, the degree of nucleophilic substitution was investigated for the derivatisation of a variety of small molecules. Whilst giving some increase in the ESI-MS response for the derivatised compounds, the FMP itself acted as a derivatising reagent in a competing reaction. In the light of this finding, FMP was reacted with the test compounds separately and gave positive results as a derivatising reagent. Detection of the ,pre-charged' derivatives of amines and carboxylic acids by LC/ESI-MS was investigated with respect to their ESI response and chromatography. Copyright © 2003 John Wiley & Sons, Ltd. [source] Preparation of Core-shell Microspheres by ATRP Synthesized MacromonomerCHINESE JOURNAL OF CHEMISTRY, Issue 10 2008Hong CHU Abstract Poly(tert -butyl methacrylate) macrointermediates (PtBMA-Br) with an end of bromine atom were synthesized by atom transfer radical polymerization using ethylbromopropionate as an initiator in bulk in the presence of N,N,N,,N,,,N,, -pentamethyl diethylenetriamine (PMDETA) as a single ligand. A new macromonomer (MAA- PtBMA) was successfully prepared via end-group nucleophilic substitution with methacrylic acid to attain a high efficiency of C=C incorporation. The molecular weights of MAA-PtBMA macromonomers were controllable from 5400 to 11000 g/mol, and the molecular weight distribution was narrow (,1.20). Then, the PtBMA graft polystyrene (PtBMA-g-PSt) microspheres were prepared by dispersion copolymerization of MAA-PtBMA macromonomers with styrene using 2,2,-azobisisobutyronitrile as a free radical initiator in ethanol. The resulting PtBMA-g-PSt microspheres were regulated in diameter on a micron scale. [source] Diastereoisomeric assignment in a pacifenol derivative using vibrational circular dichroism,CHIRALITY, Issue 1E 2009Marcelo A. Muñoz Abstract The configuration of a chiral center in semisynthetic (,)-(2R,5R,5aR,8,,9aS)- 2,8-dibromo-2,5,9,9a-tetrahydro-5-hydroxy-5,8,10,10-tetramethyl-6H -2,5a-methano-1-benzoxepin-7(8H)-one (3 or 4), prepared in two steps from (,)-(2R,5R,5aR,7S,8S,9aS)-2, 7-dibromo-8-chloro-2,5,7,8,9,9a-hexahydro-5,8,10,10-tetramethyl-6H -2,5a-methano-1-benzoxepin-5-ol, known as pacifenol 1, has been determined using vibrational circular dichroism (VCD) measurements. The vibrational spectra (IR and VCD) of diastereoisomers 3 and 4 were calculated using density functional theory (DFT) at the B3LYP/DGDZVP level of theory for the two conformers that in each case account for the total energetic distribution found in the first 10 kcal/mol range. The DFT conformational optimization of the 8R diastereoisomer 3 indicates the cyclohexanone exists almost exclusively in a boat conformation with a ,-equatorial bromine atom and an ,-axial methyl group at the chiral center alpha to the carbonyl group, while for the 8S diastereoisomer 4 a 5:1 conformational distribution in favor of a chair conformation with an ,-axial bromine atom and a ,-equatorial methyl group is calculated, suggesting due to well-known chair versus boat relative stabilities that the plausible diastereoisomer would be the 8S molecule. A comparison of the IR spectrum of the reaction product with the calculated spectra of 3 and 4 provided no means for the diastereoisomeric assignment, while from comparison of the VCD spectra it became immediately evident that the rearranged molecule possesses the 8R absolute configuration as shown in 3, in concordance with a single crystal X-ray diffraction study that could be refined to an R -factor of 2.9%. Chirality 21:E208,E214, 2009. © 2009 Wiley-Liss, Inc. [source] Reactions of BBrn+ (n = 0,2) at fluorinated and hydrocarbon self-assembled monolayer surfaces: observations of chemical selectivity in ion,surface scatteringJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 7 2001Nathan Wade Abstract Ion,surface reactions involving BBrn+ (n = 0,2) with a fluorinated self-assembled monolayer (F-SAM) surface were investigated using a multi-sector scattering mass spectrometer. Collisions of the B+ ion yield BF2+ at threshold energy with the simpler product ion BF+· appearing at higher collision energies and remaining of lower abundance than BF2+ at all energies examined. In addition, the reactively sputtered ion CF+ accompanies the formation of BF2+ at low collision energies. These results stand in contrast with previous data on the ion,surface reactions of atomic ions with the F-SAM surface in that the threshold and most abundant reaction products in those cases involved the abstraction of a single fluorine atom. Gas-phase enthalpy data are consistent with BF2+ being the thermodynamically favored product. The fact that the abundance of BF2+ is relatively low and relatively insensitive to changes in collision energy suggests that this reaction proceeds through an entropically demanding intermediate at the vacuum,surface interface, one which involves interaction of the B+ ion simultaneously with two fluorine atoms. By contrast with the reaction of B+, the odd-electron species BBr+· reacts with the F-SAM surface to yield an abundant single-fluorine abstraction product, BBrF+. Corresponding gas-phase ion,molecule experiments involving B+ and BBr+· with C6F14 also yield the products BF+· and BF2+, but only in extremely low abundances and with no preference for double fluorine abstraction. Ion,surface reactions were also investigated for BBrn+ (n = 0,2) with a hydrocarbon self-assembled monolayer (H-SAM) surface. Reaction of the B+ ion and dissociative reactions of BBr+· result in the formation of BH2+, while the thermodynamically less favorable product BH+· is not observed. Collisions of BBr2+ with the H-SAM surface yield the dissociative ion,surface reaction products, BBrH+ and BBrCH3+. Substitution of bromine atoms on the projectile by hydrogen or alkyl radicals suggests that Br atoms may be transferred to the surface in a Br-for-H or Br-for-CH3 transfer reaction in an analogous fashion to known transhalogenation reactions at the F-SAM surface. The results for the H-SAM surface stand in contrast to those for the F-SAM surface in that enhanced neutralization of the primary ions gives secondary ion signals one to two orders of magnitude smaller than those obtained when using the F-SAM surface, consistent with the relative ionization energies of the two materials. Copyright © 2001 John Wiley & Sons, Ltd. [source] Radical copolymerization of vinylidene fluoride with 1-bromo-2,2-difluoroethyleneJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2010G. K. Kostov Abstract The radical copolymerization of vinylidene fluoride (VDF) and 1-bromo-2,2-difluoroethylene (BDFE) in 1,1,1,3,3-pentafluorobutane solution at different monomer molar ratios (ranging from 96/4 to 25/75 mol %) and initiated by tert -butylperoxypivalate (TBPPI, mainly) is presented. Poly(VDF- co -BDFE) copolymers of various aspects (from white powders to yellow viscous liquids) were produced depending on the copolymer compositions. The microstructures of the obtained copolymers were characterized by 19F and 1H NMR spectroscopy and by elementary analysis and these techniques enabled one to assess the contents of both comonomers in the produced copolymers. VDF was shown to be more incorporated in the copolymer than BDFE. From the extended Kelen and Tudos method, the kinetics of the radical copolymerization led to the determination of the reactivity ratios, ri, of both comonomers (rVDF = 1.20 ± 0.50 and rBDFE = 0.40 ± 0.15 at 75 °C) showing that VDF is more reactive than BDFE. Alfrey-Price's Q and e values of BDFE monomer were calculated to be 0.009 (from QVDF = 0.008) or 0.019 (from QVDF = 0.015) and +1.22 (vs. eVDF = 0.40) or +1.37 (vs. eVDF = 0.50), respectively, indicating that BDFE is an electron-accepting monomer. Statistic cooligomers were produced with molar masses ranging from 1,800 to 5,500 g/mol (assessed by GPC with polystyrene standards). A further evidence of the successful copolymerization was shown by the selective reduction of bromine atoms in poly(VDF- co -BDFE) cooligomers that led to analog PVDF. The thermal properties of the poly(VDF- co -BDFE) cooligomers were also determined and those containing a high VDF amount exhibited a high thermal stability. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3964,3976, 2010. [source] Thermal degradation of a brominated bisphenol a derivativePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 11-12 2003M. P. Luda Abstract The thermal degradation of 2,6,2,,6,,tetrabromo-4,4,-isopropylidene-di phenol (tetrabromobisphenol A) (TBBPA) has been investigated and a mechanism for its thermal degradation is suggested. TBBPA is a comonomer widely used in epoxy and in unsaturated polyester resins to impart fire retardance. These resins find a common use in electric and electronic equipment. The presence of bromine atoms is the key factor in fire retardant activity, while on the other hand it represents an ecological problem when pyrolytic recycling is programmed at the end of the useful life of such items. However, pyrolysis is the more advantageous recycling system for thermosetting resins and thus efforts should be made to control the pyrolysis in order to avoid or minimize the development of toxics. Homolytic scission of the aromatic bromine and condensation of aromatic bromine with phenolic hydroxyl are the main processes occurring in the range 270,340°C. A large amount of charred residue is left as a consequence of condensation reactions. HBr and brominated phenols and bisphenols are the main volatile products formed. Brominated dibenzodioxins structures are included in the charred residue and not evolved in the volatile phases. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||