Hydration structures of bromides on cationic micelles

The peripheral structures of bromides on dodecyltrimethylammonium bromide (DTAB) and hexadecyltrimethylammonium bromide (HTAB) micelles have been studied by X-ray absorption fine structure (XAFS) at the Br-K edge. The XAFS spectra indicate that water is a dominant scattering group for Br- even in these micellar solutions. However, the oscillation intensity decreases with increasing micellar concentration, suggesting that the bromides are dehydrated to some extent when they are bound to the micelles. A XAFS analysis routine gives unusually short Br-O (water) distances and is inapplicable to the present systems. This comes from the structure of the first coordination shell, in which two or more scattering paths are involved. The second scattering group is obviously the head group of the surfactants forming the micelles. The detailed analysis has allowed us to estimate the hydration number of the bromides bound on the DTAB and HTAB micelles (N = ca. 4.2). The assumption that all of the bromides form direct ion-associates with the head groups causes the contradiction to the results of the XAFS analyses. This strongly implies that some of the bromides partitioned into the micelle are completely hydrated as far as their first coordination shell is concerned. Assuming that the maximum hydration number of the bromides bound to the head groups of the micelle is three, 40% of the bromides partitioned into the micelle are completely hydrated.     

A new hexaaminomacrocycle for ditopic binding of bromide

A hexaaminomacrocycle L, containing four secondary and two tertiary amines has been synthesized and crystallized with hydrobromic acid. The structural analysis of the bromide complex suggests that the ligand in its tetraprotonated form, is involved in coordinating two bromides from both the sides via hydrogen bonding interactions with N?Br⁻ distance of 3.351 Å, forming a ditopic complex. The other two bromides are outside the cavity, and singly bonded to the macrocycle. The molecules are packed showing layer structures in which the internal bromides are locked between the layers of macrocycles. The bromide anions are coordinated alternatively by one and two hydrogen bonds with the protonated amines from the two adjacent macrocycles.     

Synthesis and transformations of triphenylpropargylphosphonium bromide

A method of the synthesis of triphenylpropargylphosphonium bromide is developed. Its isomerization and hydration in various solvents are studied, and reactions with secondary amines, triethylamine, and triphenylphosphine are carried out. It is established that secondary amines add to the intermediate allene isomer with subsequent migration of the formed double bond to the phosphorus atom. The reaction of triethylamine with triphenylpropargyl and triphenylethynyl bromides occurs similarly to alkaline hydrolysis involving attack of the amine on the phosphorus atom. Triphenylphosphine forms with triphenylpropargylphosphonium bromide a bis-salt with a terminal methylene group. Experimental evidence is obtained showing that for phosphoxazole derivatives to form from oximes derived from triphenyl(oxomethyl)phosphonium salts that latter should bear an aryl substituent at the keto group.     

Crystal structures of hydrates of simple inorganic salts. III. Water‐rich aluminium halide hydrates: AlCl3·15H2O,AlBr3·15H2O,AlI3·15H2O,AlI3·17H2O and AlBr3·9H2O

Water‐rich aluminium halide hydrate structures are not known in the literature. The highest known water content per Al atom is nine for the perchlorate and fluoride. The nonahydrate of aluminium bromide, stable pentadecahydrates of aluminium chloride, bromide and iodide, and a metastable heptadecahydrate of the iodide have now been crystallized from low‐temperature solutions. The structures of these hydrates were determined and are discussed in terms of the development of cation hydration spheres. The pentadecahydrate of the chloride and bromide are isostructural. In AlI₃·15H₂O, half of the Al³⁺ cations are surrounded by two complete hydration spheres, with six H₂O in the primary and 12 in the secondary. For the heptadecahydrate of aluminium iodide, this hydration was found for every Al³⁺.     

Rapid incorporation of radiobromine via the reaction of labeled sodium bromide with organoboranes

Organoboranes react with⁸²Br labeled sodium bromide in the presence of chloramine-T to yield the corresponding⁸²Br labeled alkyl and aryl bromides. The reaction is rapid, proceeds under mild conditions, and tolerates a variety of functional groups.     

Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K

Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium bromide, Pr₄NBr, and tetrapentylammonium bromide, Pen₄NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu₄NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me₄NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds increases systematically in going from Me₄NBr to Pen₄NBr.     

Gas phase chromatography of halides of elements 104 and 105

On-line isothermal gas phase chromatography was used to study halides of²⁶¹104 (T_1/2=65 s) and^262,263105 (T_1/2=34 s and 27 s) produced an atom-at-a time via the reactions²⁴⁸Cm(¹⁸O, 5n) and²⁴⁹Bk(¹⁸O, 5n, 4n), respectively. Using HBr and HCl gas as halogenating agents, we were able to produce volatile bromides and chlorides of the above mentioned elements and study their behavior compared to their lighter homologs in Groups 4 or 5 of the periodic table. Element 104 formed more volatile bromide than its homolog Hf. In contrast, element 105 bromides were found to be less volatile than the bromides of the group 5 elements Nb and Ta. Both 104 and Hf chlorides were observed to be more volatile than their respective bromides.     

Effect of tetra-n-alkylammonium bromides on the volumetric properties of glycine,l-alanine and glycylglycine at T=298.15 K

The effect of tetra-n-alkylammonium bromides, R₄NBr (R=CH₃, C₂H₅, C₄H₉) on the densities, ρ, of glycine, l-alanine and glycylglycine are reported at T=298.15 K. The apparent molar volumes of amino acids in aqueous tetra-n-alkylammonium salts, φ_VAJW, and of tetra-n-alkylammonium bromides in aqueous amino acids and peptide, φ_VJAW, are calculated from the measured densities. Both φ_VAJW and φ_VJAW have been analysed accurately using a simple equation. Positive transfer volumes are observed for glycine, l-alanine and glycylglycine in the presence of R₄NBr. Tetra-n-butylammonium bromide shows almost double increase in the transfer volumes of amino acids or peptide than tetramethyl- or tetraethylammonium bromides. Negative transfer volumes for the tetra-n-alkylammonium bromide salts are noted in aqueous amino acids or peptide due to large tetra-n-alkylammonium cation undergoing hydrophobic hydration.     

Molecular Rydberg transitions. Intermediate coupling in simple bromides

An intermediate coupling analysis of the low-energy π → σ Rydberg transitions of hydrogen bromide, cyanogen bromide, acetylene bromide and alkyl bromides is presented. Exchange and spin-orbit coupling parameters are calculated and their variations discussed. The Br 5s orbital is delocalized in the larger alkyl bromides and Br 4p is heavily involved in π bonding in acetylene and cyanogen bromides.     

Stability and microtox response of butenyltin compounds

Tributenyltin bromides containing double bonds at carbon atoms C-1, C-2 or C-3 were synthesized from symmetrical tetrabutenyltins. Although all three tetrabutenyltin compounds were stable, only the tributenyltin bromides with double bonds at C-1 and C-3 were sufficiently stable for further studies. In aqueous sodium bromide (NaBr) solution containing 1% acetone, tri-1-butenyltin bromide was more stable in sunlight than tri-3-butenyltin bromide, yet neither compound was as stable as tributyltin bromide. Stability in seawater, in the absence of ultraviolet (UV) light, was less for both tri-1-butenyltin bromide and tri-3-butenyltin bromide than for tributyltin bromide. The relative toxicities of the tributenyltin bromides were determined using a bioluminescent bacteria assay. The concentrations of tributenyltin bromides necessary to produce a toxic response were three to six times greater than for tributyltin bromide.     

Reaction of α,α-, α,α′-dihalothiones with 8-mercaptoquinolinium halides as a route to tetrahydro-1,4-thiazinoquinolinium halides

The reaction of 8-mercaptoquinolinium bromide with 1,3-dibromopropane-2-thione or 3,3-dibromobutane-2-thione in methanol gave the 2-bromomethyl-2-mercaptotetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium and 3-bromo-2-mercapto-2,3-dimethyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium bromides which readily exchanged the Br⁻ anion for ClO ₄ ⁻ upon treatment with sodium perchlorate in methanol. Oxidation of the 3-bromo-2-mercapto-2,3-dimethyltetrahydro-1,4-thiazino[2,3,3,4-i,j]-quinolinium bromide by selenium dioxide gave 2,2-dithiobis(3-bromo-2,3-dimethyltetrahydro-1,4-thiazino[2,3,3,4-i,j]quinolinium) bromide. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1720–1723, November, 2006.     

Mechanistic role of benzylic bromides in the catalytic autoxidation of methylarenes

Different pathways for benzylic bromide transformations were examined under conditions of cobalt-bromide catalysis in acetic acid. It has been shown that benzylic bromides participate in the catalytic cycle through their catalyzed and noncatalyzed oxidation, through their reaction with Co(III), and through cobalt(II)-catalyzed solvolysis. The rates of the direct reduction of Co(III) by several benzylic bromides were measured under an argon atmosphere; the reaction occurs by a mechanism involving two forms of Co(III). The same reaction under an oxygen atmosphere initiates the cobalt-bromide-catalyzed oxidation of benzyl bromide, thus leading to the regeneration of inorganic bromide and the fast reduction of Co(III). Solvolysis of benzylic bromides plays only a minor role in the regeneration of inorganic bromide in glacial acetic acid.     

Thermodynamic properties of aqueous solutions of tetraalkylammonium salts: Dependence of the hydrophobic hydration effect on the cation size

The heats of solution of tetrahexylammonium and tetraheptylammonium bromides in water were measured at 318.15 and 328.15 K. The standard enthalpies and specific heats of solution and the temperature changes in the free energy and entropy of solution were calculated. A comparison of the thermodynamic properties of solutions for the homologous series of tetraalkylammonium salts demonstrated that the enthalpic, entropic, and specific heat characteristics of solution are positive and increase almost linearly up to tetrapentylammonium bromide. On passing to larger homologues, these parameters decrease, suggesting that the hydrophobic hydration effect is substantially weaker in solutions of tetraalkylammonium salts with larger cations. Original Russian Text ? A.V. Kustov, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 2, pp. 368–373.     

Laser-excited molecular flourescence spectrometry for the determination of traces of nonmetals : Part 1. determination of traces of fluoride,chloride and bromide based on diatomic molecules in a graphite furnace

For the determination of flouride, chloride and bromide, a suitable metal ion is added in a modified graphite tube atomizer. After drying and ashing, the substances are vaporized and diatomic molecules between the metal and nonmetal are formed. These molecules are excited by a pulsed dye laser and the resulting fluorescence is measured. At constant metal concentration, the fluorescence is proportional to the halide concentration. The diatomic molecules used are MgF, InCl and AlBr. The detection limits are 11 pg of fluoride, 15 pg of chloride and 70 pg of bromide in the 10-μl injections, corresponding to 6 x 10^?8 mol l^?1 fluoride, 4 x 10^?8 mol l^?1 chloride and 9 x 10^?8 mol l^?1 bromides.     

On the reactivity of N-benzylpyrimidinium salts with nitrogen nucleophiles

Treatment of the l-benzyl salts of pyrimidine, 4,6-dimethylpyrimidine, and 4-t-butylpyrimidine with liquid ammonia leads to debenzylation. The ¹H-nmr spectroscopic evidence is presented that the initial step in the debenzylation of l-benzyl-4,6-dimethylpyrimidinium bromide is the addition of the ammonia at C-2, while with l-benzyl-4-t-butylpyrimidinium bromide the addition takes place at C-6. It is proved by ¹⁵N labelling that the debenzylation occurs according to the ANRORC mechanism. The above-mentioned l-benzylpyrimidinium bromides give with hydrazine, pyrazole, 3,5-dimethylpyrazole and 3-t-butylpyrazole, respectively.     

Substrate-Mediator Duality of 1,4-Dicyanobenzene in Electrochemical C(sp2)−C(sp3) Bond Formation with Alkyl Bromides

Electrochemical approaches to form C(sp²)−C(sp³) bonds have focused on coupling C(sp³) electrophiles that form stabilized carbon-centered radicals upon reduction or oxidation. Whereas alkyl bromides are desirable C(sp³) coupling partners owing to their availability and cost-effectiveness, their tendency to undergo radical-radical homocoupling makes them challenging substrates for electroreductive cross-coupling. Herein, we disclose a metal-free regioselective cross-coupling of 1,4-dicyanobenzene, a useful precursor to aromatic nitriles, and alkyl bromides. Alkyl bromide reduction is mediated directly by 1,4-dicyanobenzene radical anions, leading to negligible homocoupling and high cross-selectivity to form 1,4-alkyl cyanobenzenes. The cross-coupling scheme is compatible with oxidatively sensitive and acidic functional groups such as amines and alcohols, which have proven difficult to incorporate in alternative electrochemical approaches using carboxylic acids as C(sp³) precursors.     

Phenacyl bromide: A versatile organic intermediate for the synthesis of heterocyclic compounds

Phenacyl bromides are used as a building blocks in synthetic organic chemistry, which serves as a key model for the development of various biologically important heterocyclic compounds and other industrially important scaffolds. This review covers recent synthetic advances in the preparation of heterocyclic compounds utilizing various phenacyl bromides. A wide range of five- and six-membered heterocyclic compounds as well as fused heterocyclic compounds were synthesized efficiently from the phenacyl bromide precursors through one-pot multicomponent reactions.     

Conversion of Alcohols to Bromides by Trimethylsilane and lithium Bromide in Acetone

Conversion of alcohols to alkyl bromides is one of the most frequently used functional group transformation reactions. Phosphorus tribromide is one of the most popular classical reagents. Triphenylphosphine has been used in combination with bromine,carbon tetrabromide,N-halo imides and other bromide compounds as a mild reagents for the preparation of alkyl bromides. More reacently, halotrimethylsilanes were found to be useful for halogenation of alcohols. Geo- rge A.Olah successfully convert…     

A facile one-pot synthesis of α-fluoro-α,β-unsaturated esters from alkoxycarbonylmethyltriphenylphosphonium bromides

A convenient one-pot synthesis of α-fluoro-α,β-unsaturated esters from ethoxy- and tert-butoxycarbonylmethyltriphenylphosphonium bromide was developed. The fluorinated phosphoranes, generated in situ from alkoxycarbonylmethyltriphenylphosphonium bromides and 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (Selectfluor^®), undergo a Wittig reaction with aldehydes to yield α-fluoro-α,β-unsaturated esters with (Z)-selectivity.