Excess Bromine Research Articles

Photo-bromination and photo-induced graft polymerization as a two-step approach for surface modification of polyacrylonitrile ultrafiltration membranes

A two-step heterogeneous polymer surface modification was developed, involving photo-bromination as activation and subsequent UV-induced graft polymerization with acrylic monomers. With polyacrylonitrile (PAN) ultrafiltration (UF) membranes, extent and effects of photo-bromination compared with the thermal reaction were studied with gravimetry, diffuse reflectance UV and ATR-IR spectroscopy, and scanning electron microscopy (SEM) as well as the UF properties. The yields of thermal and photo-bromination reached constant values of about 60 and 150 μmol g , after 24 and 3 hr, respectively. The former Br content was assigned to Br 2 addition to double bonds, the latter to Br-radical CH substitution plus addition products. Excess bromine was bound as a charge-transfer complex to PAN nitrile groups, causing partially irreversible changes of the membrane matrix indicated by UF permeability reductions. The formation of polymer radicals after UV irradiation of photo-brominated PAN was verified with ESR spectroscopy. UV irradiation-induced graft polymerization of acrylic acid and methyl acrylate from the gas phase on to PAN membranes was accomplished. It was found that activation by thermal bromination is sufficient to initiate heterogeneous graft polymerization. Sorbed bromine promoted homopolymerization, increasing concentrations of hydroquinone improved the grafting efficiency. The graft-polymer modified surfaces were characterized by ATR-IR, SEM and contact angles. A pronounced selectivity towards the UV exposed membrane surface was achieved. For relatively low degrees of modification (up to 150 μg/cm 2), thin and smooth graft polymer layers were created which specifically altered the membrane surface hydrophilicity. UF membrane permeability and selectivity were a direct function of the degree of modification, suggesting adjustability of average separation layer pore size.

Darstellung und 11B-NMR-Spektrum von Heptabromo-closo-heptaborat, [B7Br7]2- sowie Kristallstruktur von [(C5H5N)2CH2][B7Br7] / Preparation and 11B NMR Spectrum of Heptabromo-closo-heptaborate, [B7Br7]2-, and the Crystal Structure of [(C5H5N)2CH2][B7Br7

By reaction of conjuncto-[B6H6-B6H6]2- in alkaline solution with excess bromine the heptabromo-closo-heptaborate, [B7Br7]2 is formed. The crystal structure of [(CsH3N)2CH2][B7Br7] has been determined by single crystal X-ray diffraction analysis (monoclinic, space group P21/a with a = 15.0843(14), b = 9.8882(14), c = 17.057(2) Å, β = 114.039°(7)). In accordance with the D5h point symmetry, the anion shows two singlets at -23.3 and -0.1 ppm with the intensity ratio 2:5 in its 11B NMR spectrum.

Intramolecularly Coordinated Low-Valent Organotellurium Complexes Derived from 1-(Dimethylamino)naphthalene

A series of low-valent intramolecularly coordinated organotellurium compounds incorporating the 8-(dimethylamino)-1-naphthyl group has been synthesized by the organolithium route. Insertion of elemental tellurium into the Li−C bond of RLi (2) affords the tellurolate RTeLi (3) (R = 8-(dimethylamino)-1-naphthyl). Oxidative workup of 3 gives dark red ditelluride 4 in moderate yield. Reaction of 2 with “PhTeBr” afforded telluride 5. Interestingly, the reaction of 2 with TeI2 afforded the stable tellurenyl iodide 6 instead of the expected telluride R2Te. Controlled bromination of ditelluride with bromine in chloroform gave stable tellurenyl bromide 7 whereas bromination with excess bromine leads to the isolation of tellurium(IV) tribromide 8. Ditelluride 4 was found to be inert to the reactions with diazomethane and reducing agents like NaBH4, NaH, and LiAlH4. The compounds were characterized by elemental analysis, NMR (1H, 13C, 125Te), and mass spectroscopic techniques. For three of these compounds R2Te2 (4),...

Synthesis, characterisation and reactions of bis[2-(dimethylaminomethyl)-phenyl] diselenide: its structure and that of [2-(dimethylaminomethyl)phenyl]-selenium bromide

Bis[(2-dimethylaminomethyl)phenyl] diselenide (RSe)2 was obtained by the organolithium route. It underwent facile reaction with stoichiometric amounts of bromine and iodine to give the corresponding arylselenium halides RSeBr and novel RSeI in which the selenium is covalently bonded to iodine. With an excess of bromine it gave the corresponding tribromide RSeBr3 but a similar reaction with iodine gave only RSeI. With diazomethane it gave the selenoether (RSe)2CH2 and with HCl the known bis(hydrochloride)(RSe)2·2HCl. A catalytic conversion of alkenes into allylic acetates using (RSe)2 was carried out. The compounds were characterised by elemental analyses, mass, multinuclear NMR (1H, 13C, 77Se), IR, Fourier-transform-Raman spectrometry and conductance measurements. The compound RSeBr3 shows evidence for the existence of Se ⋯ N interaction in solution and was found to equilibrate between co-ordinated and non-co-ordinated forms. The structures of the diselenide (RSe)2 and its bromo derivative RSeBr were determined by X-ray crystallography. The compounds are isostructural and exhibit Se ⋯ N intramolecular co-ordination. The Se atom has T-shaped three-co-ordination in both structures and the five-membered chelate rings formed by the Se, C and N atoms are puckered and exist in an envelope conformation. The Se ⋯ N interaction in RSeBr [Se–N 2.143(6)A] is, however, considerably stronger than that in (RSe)2[Se(1)–N(1) 2.856(3), Se(2)–N(2) 2.863(4)A].

Study of the complexation chemistry and speciation of thallium for on-line preconcentration with immobilised quinolin-8-ol

The effects of various buffering reagents and pH conditions were investigated by flame atomic absorption spectrometry to optimise complexation of T13+ with quinolin-8-ol (8-Q), immobilised on controlled-pore glass beads in a 5-cm column. As Tl3+ is a softer acid than the other trivalent cations of the Group III elements, the effects of the buffers are different from those observed previously for Al3+, Ga3+ and In3+. A mixed buffer of 0.1 mol l−1 acetate and 0.1 mol l−1 ammonium chloride at pH 10 proved most successful, although 0.1 mol l−1 maleate was also satisfactory over a pH range of 4–10. As thallium normally exists as Tl+ in solution, an oxidation method was developed to convert the ions to Tl3+, which is more efficiently complexed by 8-Q. Addition of 1–10 μl of bromine per 100 ml of sample was sufficient to oxidise Tl+ without heating. Excess bromine was removed by addition of phenol. With a flow-rate of 6 ml min−1, the detection limit of Tl3+ is 3 ng ml−1, for a 3-miri preconcentration time. The enrichment factor under these conditions is 55 and the characteristic concentration is 2 ng ml−1. The major ions in sea water did not interfere with Tl3+ preconcentration and the tolerable limits of Fe3+, Cu2+ and Al3+ are high enough to permit analysis of river and sea waters. The method was applied successfully to the determination of thallium in potassium-enriched table salt. It was also shown that the concentrations of Tl+ and Tl3+ in a solution can be derived using the described procedure, allowing speciation of inorganic thallium.

Sites of successive bromination of the ambident nucleophiles 2-methoxy-, 2,4-dimethoxy- and 2,4,6-trimethoxy-benzylidenefluorenes and 2,2-dimesityl-1-tert-butylethenol

The reaction of the 2-methoxy-2a, 2, 4-dimethoxy-2c and 2, 4, 6-trimethoxy-benzylidenefluorene 2d with bromine in AcOH has been investigated. With compound 2a the initial product is the α, 9′-dibromide 3a which, with excess of bromine, gives the α, 5, 9′-tribromo derivative 3c. In NaOAc–AcOH compound 3a gives both debromination to 2a and dehydrobromination to 1a and 3b gives the α, 5-dibromo derivative 5a. Compounds 2c and 2d give successively the 5-bromo- and 3-bromo-4b and 4c and the α, 5-dibromo- and α, 3-dibromo-5b and 5c derivatives and further bromination of compound 2d gives, first, the α, 3, 5-tribromo-6 and then the α, 3, 5, 2′, 7′-pentabromo-7 derivatives. Higher sensitivity to substituents of the α-aryl ring compared with the double bond towards electrophilic bromine and accompanying increased steric shielding of the double bond account for this order. Bromination of 2, 2dimesityl-1 -tert-butylethenol 11 gives mainly ring-brominated 2, 2-dimesityl-1 -tert-butylethanones 12–14 and several other derivatives.

Improved synthesis of α‐L‐Fuc(1→4)‐β‐D‐GlcNAc and α‐L‐Fuc(1→6)‐β‐D‐GlcNAc building blocks: A convergent strategy employing 4‐O→6‐O acetyl migration; NOE data of the protected α‐1,4‐linked disaccharide

AbstractThe synthesis of the two ethylthio disaccharide building blocks 10 and 17 was achieved by coupling of fucosyl bromide 9 with the acceptor alcohols 6 and 7 under in situ anomerization conditions. The selectively protected 2‐deoxy‐2‐phthal‐imidoglucose derivative 7 was derived from 6 by utilizing an optimized acetyl migration reaction. The ethylthio function in disaccharides 10 and 17 was activated with bromine, and excess bromine was removed with cyclohexene. The sensitive 1,6‐linkage in the disaccharide 10 proved to be stable under these activating conditions. The disaccharide bromides 11 and 18 were treated with methanol to afford after deblocking the methyl glycosides 16 and 23. Homonuclear 1H‐NOE data were obtained for the protected 1,4‐linked disaccharide 17 suggesting that its preferred solution conformation is rather similar to the solution conformation of the deblocked disaccharide 23 in aqueous solution as known from literature data.

Some observations on the titrimetric determination of some arylphthalides

A new titrimetric method for the determination of 3- p-anisyl-, 3-(3′-bromo-4′-hydroxyphenyl)-, and 3-(4′-hydroxyphenyl)phthalides and phenolphthalein has been developed. The method is based on their reaction with an excess of bromine to form hypobromites. After the removal of the excess bromine with formic acid, the hypobromites are treated with iodide to liberate an equivalent amount of iodine, which can be determined titrimetrically with thiosulfate using starch as an indicator. The recovery range is 96.5–100.4% and the coefficient of variation is 0.4–1.5% depending on the concentration levels of the studied compounds.

Arctic boundary layer ozone variations associated with nitrate, bromine, and meteorology: A case study

Gas and aerosol measurements at Barrow, Alaska during the spring of 1986 confirm the inverse relationship between particulate excess bromine (xBr) and O3. In addition to this inverse XBr‐O3 relationship, several other factors were found to be important in understanding the springtime variability of O3 at Barrow. They are (1) O3 concentration variability associated with NOx chemistry at high pollutant levels or transport of primary pollutant O3 from lower latitudes, (2) displacement of air masses of high O3 content with air masses low in O3 but high in sea salt, suggesting potential roles of sea salt in O3 fluctuations, and (3) when pollutant levels were low, advection of air that can cause gradual change in O3 with more rapid inversely related fluctuations of O3 and xBr superimposed. Under the conditions of factor 3 the trend and anticorrelation each accounted for about one quarter of the variance in O3, suggesting a role for other compounds or low level reactive nitrogen species and gas‐particle interaction in the photolytic O3 destruction process.

Determination of altenuene and isoaltenuene by liquid chromatography—electrochemical detection with on-line generated bromine

The electroinactiveAlternaria mycotoxins, altenuene and isoaltenuene, are separated by reversed-phase liquid chromatography and derivatized (post-column) with electrochemically generated bromine. Bromine is produced, on-line, by a coulometric cell and the excess of bromine, after reaction with the analyte in the column effluent, is electrochemically detected. The proposed method compares well in term of sensitivity with existing techniques for the determination of altenuene and isoaltenuene in artificially contaminated samples and, in addition, is superior in terms of selectivity. At a signal-to-noise ratio of 3 the detection limit is 8 ng on column. The relationships between generating current, signal and noise are given.

Multielemental composition of the Arctic aerosol

A series of 12 daily aerosol samples was collected during March 1985 at Alert, Canada. Trace elemental composition and ion analysis was performed on the samples employing the techniques of instrumental neutron activation analysis and ion chromatography. Current knowledge, enrichment factor calculations, and regression analysis suggest four main constituent sources for the Arctic aerosol in this period: crustal, oceanic, anthropogenic, and photochemical reactions of marine Br compounds. Elements derived mainly from crustal sources are Al, Ca, Ce, Co, Fe, K, La, Mn, Sc, Sm, Th, and Ti. Oceanic‐derived elements include Cl, I, and Na, while anthropogenic sources include As, In, NO3‐, NH4+, Sb, Se, SO4= and V. The source of zinc remains ambiguous. Elemental ratios give supporting evidence that anthropogenic sources have their origin in Eurasia. Calculations of excess bromine in the late winter confirm results of previous experiments done in the Arctic.

Specific demonstration of ribonucleic acid by chemical bromination and immunohistochemistry.

In this report we describe a specific staining procedure for detection of ribonucleic acid (RNA), based on bromination of uracil and subsequent immunohistochemical visualization of 5-bromouracil in RNA. This method is applicable for both cryostat and glycol methacrylate (GMA)-embedded sections. Cryostat sections must be fixed in formaldehyde, whereas tissue pieces to be embedded in GMA are fixed in cold acetone. Before bromination, sections must be treated with trypsin. Bromination was performed in a solution of bromine in potassium bromide. After bromination, excess bromine was removed with sodium bisulfite. The monoclonal antibody MoBu-1 specifically bound to brominated RNA. Ribonuclease digestion, in contrast to deoxyribonuclease digestion, abolished staining. This method makes possible precise localization of RNA, especially well demonstrated in plastic-embedded sections.

ChemInform Abstract: Formation of Pentabromide Ions from Bromine and Bromide in Moderate‐Polarity Aprotic Solvents and Their Possible Involvement in the Product‐Determining Step of Olefin Bromination.

AbstractThe results of a UV‐VIS spectrophotometric investigation show that a pentabromide species is formed, besides the tribromide, when Bu4N+Br‐ and excess bromine are dissolved in 1,2‐dichloroethane.

Synthesis and stability of Br 2, ICI and IBr intercalated pitch-based graphite fibers

This work presents a further study of the intercalation of halogens in pitch-based fiber and the stability of the resultant intercalation compounds. P-100 fibers were intercalated with purified IBr at 50 °C to produce high electrical conductivity graphite intercalation compounds (GICs). After intercalation and subsequent equilibration in ambient atmosphere, the fibers average a five-fold conductivity,enhancement over the pristine fiber, and after nine weeks in air, the conductivity, σ, degrades by only 1%. The intercalation of ICl in P-100 was performed in vacuum-sealed vessels at 50 °C, 20° and 0 °C. Both the lowest equilibrium resistivity and its smallest ambient gain were observed for fibers reacted at 20 °C. P-100 brominated at 68 °C in vacuum-sealed vessels showed no loss in electrical and stability properties over those reacted at 20 °C in the presence of air. Energy dispersive spectroscopy (EDS) results confirm the existance of excess bromine and chlorine in the iodine interhalide GICs, which is predicted by the oxidation mechanism proposed for this class of intercalation reactions.

Colorimetric and Bromometric Determination of Pirbuterol Hydrochloride

Abstract Two proposed methods are reported for the quantitation of pirbuterol hydrochloride, namely, (i) colorimetric and (ii) titrimetric methods. The colorimetric method is based on coupling betweem diazotized sulphanilamide and pirbuterol hydrochloride. Under the optimum conditions studied, the coupling product exhibits a maximum at 440 nm. Linear relation between absorbance, A, and concentration of pirbuterol hydrochloride is in the range 5–40 μgml−1. The mean percentage obtained for capsules (ExirelR −15 mg) was 100.8 ± 0.7 whereas mean percentage recovery obtained for the authentic drug was 100.5 ± 0.8. The titrimetric procedure involves bromination of authentic pirbuterol in acid medium and residual titration of excess bromine. The stoichiometry of the reaction was investigated and infra-red analysis, of the bromoderivative was carried out. When applied to capsules the bromometric method gave mean percentage of 100.18 ± 2.25.

An Indirect Coulometric Determination of some Aromatic Amines with Generated Bromine

Abstract The possibilities of determining benzidine, 3, 3′ -dimethyl-benzidine, 1-naphtylamine and 2,4-diaminotoluene with coulo-metrically generated bromine were studied. Conditions have been found for an indirect determination of 3,3′-dimethylben-zidine and 2,4-diaminotoluene based on the reaction with excess bromine. With 3,3 -dimethylbenzidine, the unreacted bromine is reduced with excess arsenic (III) that is back-titrated with coulometrically generated bromine. With 2,4-diamino-toluene, the excess bromine is titrated with copper (I) that is coulometrically generated in the same base electrolyte after changing the polarity of the generating electrode. Analytical use of the reactions of benzidine and 1-naphtylamine with bromine is prevented by non-stoichiometric courses of the reactions.

ChemInform Abstract: A One‐Step Preparation of 4‐Bromomethyl‐2,3,5,6‐tetrabromophenol.

AbstractHeating p‐cresol (I) with excess bromine in the presence of aluminum trichloride yields 4‐bromomethyl‐2,3,5,6‐tetrabromophenol (II) which is a starting material for the preparation of several flame retardants.

Bromine oxidation of a nickel(II) bis(oxime-imine) complex. Evidence for a single-step outer-sphere two-electron transfer?

The kinetics and mechanism of the two-electron oxidation of the sexidentate bis(oxime-imine) complex of nickel(II), (Ni/sup II/L) (I), by bromine have been investigated in bromide ion media over the pH range 3.1-7.6 at 25/sup 0/C and 1.0 M ionic strength. In the presence of an excess of bromine or nickel(II), oxidation is monophasic, and the initial product is (Ni/sup IV/L)/sup 2 +/, a formal nickel(IV) species that undergoes subsequent reactions to give an unknown oxidation product with excess bromine at pH > 6 or to give (Ni/sup III/L)/sup +/ by comproportionation with excess nickel(II) at pH > 5. The sole kinetically important oxidant is Br/sub 2/, and second-order rate constants for reaction of (Ni/sup II/L) and its protonated form (Ni/sup II/LH)/sup +/ are 2.1 x 10/sup 7/ and 7.1 x 10/sup 5/ M/sup -1/ s/sup -1/, respectively. These rate constants are in line with a rate-determining single-electron-transfer reaction, and the proposed mechanism involves formation of a transient ion pair (Ni/sup III/L/sup +/,Br/sub 2//sup -/ in which the rate of subsequent electron transfer is comparable with the rate of ion-pair dissociation. In addition, the pulse-radiolysis technique has been used to investigate the reactions of nickel(II) with Br/sub 2//sup -/ to givemore » (Ni/sup III/L)/sup +/, and rate constants for (Ni/sup II/L) and (Ni/sup II/LH)/sup +/ are 8.5 x 10/sup 8/ and 2.7 x 10/sup 8/ M/sup -1/ S/sup -1/, respectively, at 21/sup 0/C. 34 references, 3 figures, 3 tables.« less

ChemInform Abstract: Bromination of Tris(1,1,1‐trifluoro‐2,4‐pentanediono)rhodium(III).

AbstractBromination of the title compound is performed at room temp. (complete within 6 d) using excess bromine in CHCl3.

Bromimetric titrimetry involving the determination of bromide ions and their oxidation products

This paper describes some improvements in bromimetric titrimetry which are based on the determination of bromide and its oxidation products formed in the reaction instead of residual bromine. These modifications are particularly applicable to compounds capable of undergoing substitution or oxidation reactions. Substances which only undergo addition reactions do not affect the determination. The determination of bromide is based on oxidation with chloramine T to bromine in the presence of acetanilide, which acts as a bromine scavenger; the residual chloramine T is then determined. The bromine oxidation products of certain organic and inorganic compounds formed on reaction with excess bromine can be determined iodimetrically after the destruction of unreacted bromine with acetanilide. The methods have been tested for the determination of (i) bromide in pharmaceuticals, (ii) a variety of organic compounds through bromide formation (e.g., hydrazine, thiourea, allylthiourea, cystine, homocystine, methionine, phenol and aniline), (iii) certain substances through their oxidation product with bromine (e.g., cyanide, thiocyanate, thallium, 4-aminophenol, hydroquinone, 4-anisidine and thiosemicarbazide) and (iv) mixtures of thiocyanate and cyanide (in polluted water), hydroquinone, thiocyanate and metol (in photographic developers) and phenacetin and paracetamol (in drugs).