Showing papers on "Bromide published in 1976"

Effects of halides and bicarbonate on chloride transport in human red blood cells.

Abstract: Chloride self-exchange was determined by measuring the rate of 36Cl efflux from human red blood cells at pH 7.2 (0 degrees C) in the presence of fluoride, bromide, iodide, and bicarbonate. The chloride concentration was varied between 10--400 mM and the concentration of other halides and bicarbonate between 10--300 mM. Chloride equilibrium flux showed saturation kinetics. The half-saturation constant increased and the maximum flux decreased in the presence of halides and bicarbonate: the inhibition kinetics were both competitive and noncompetitive. The competitive and the noncompetitive effects increased proportionately in the sequence: fluoride less than bromide less than iodide. The inhibitory action of bicarbonate was predominantly competitive. The noncompetitive effect of chloride (chloride self-inhibition) on chloride transport was less dominant at high inhibitor concentrations. Similarly, the noncompetitive action of the inhibitors was less dominant at high chloride concentrations. The results can be described by a carrier model with two anion binding sites: a transport site, and a second site which modifies the maximum transport rate. Binding to both types of sites increases proportionately in the sequence: fluoride less than chloride less than bromide less than iodide.

Reaction of dimethylphenacylsulfonium bromide with N-nitrosoacetarylamides and reactions of the products with nucleophiles.

Abstract: The azo coupling of dimethylphenacylsulfonium bromides (I) with N-nitrosoacetanilides in nonaqueous solvents, and with diazotized aniline in aqueous media gave 2-bromophenylglyoxal 2-arylhydrazones (V) and the tetrazine (VI), respectively. V reacted with nucleophiles displacing the bromide. Treatment of V with bases gave VI via benzoylphenylnitrilimine (X). 1,3-Dipolar cycloadditions of X onto ethyl acrylate and acrylonitrile afforded the expected cycloadducts. The mechanisms of the reactions are outlined.

Conversion of alkyl chlorides to bromides, selective reactions of mixed bromochloroalkanes, and halogen exchange.

Abstract: Primary alkyl chlorides are quantitatively converted to their corresponding bromides in the presence of ethyl bromide, N-methyl-2-pyrrolidinone, and a catalytic amount of metal bromide. A variety of chlorides can be converted. Selective functionalization at bromine of several primary bromochloroalkanes was studied in conjunction with the chloride-bromide conversion for multistep syntheses. Methods for halogen exchange between chloride, bromide, and iodide in the octyl halide series are presented.

Photodissociation of methyl chloride and methyl bromide in the atmosphere

Abstract: Methyl chloride (CH3Cl) and methyl bromide (CH3Br) have been suggested to be significant sources of the stratospheric halogens. The breakup of these compounds in the stratosphere by photodissociation or reaction with OH releases halogen atoms which catalytically destroy ozone. Experimental results are presented for ultraviolet photoabsorption cross sections of CH3Cl and CH3Br. Calculations are presented of loss rates for the methyl halides due to photodissociation and reaction with OH and of mixing ratios of these species in the stratosphere.

Reductive demercuration of hex-5-enyl-1-mercuric bromide by metal hydrides. Rearrangement, isotope effects, and mechanism

Abstract: The use of the rearrangement of hex-5-enyl radical intermediates as a mechanistic probe has been examined in the reductive demercurations of hex-5-enyl-l-mercuric bromide (1). Methylcyclopentane and 1-hexene are the major products from reductions of 1 by sodium borohydride, lithium aluminum hydride, and tri-n-butyltin hydride. The formation of methylcyclopentane and the absence of cyclohexane are consistent with a noncage, free-radical chain mechanism for these reductions. The sodium amalgam reduction of 1 produces only 1-hexene. Hex-5-en-l-ol and a peroxide are formed from sodium borohydride reductions of 1 in the presence of molecular oxygen. Isotope effects for transfer of hydrogen to the intermediate hex-5-enyl radicals have been determined from the 1-hexene/methylcyclopentane product ratio, since rearrangement of the 5-hexenyl radical competes with hydrogen abstraction. The magnitude of these isotope effects (1.8 +- 0.2) is the same for reductive demercurations of 1 by sodium borohydride, lithium aluminum hydride, and tri-n-butyltin hydride; these results provide evidence for a common hydrogen-transfer agent, such as hex-5-enyl-1-mercuric hydride, for all of these metal-hydride reductions. The validity of the competing rearrangement method of determining hydrogen isotope effects has been demonstrated by determining the isotope effect for the tri-n-butyltin hydride reduction of 6-bromo-1-hexene (2.8 +- 0.2) at 40/sup 0/C.

Bonding studies of compounds of Group 3–5 elements. Part XVIII. He(I) photoelectron spectra of bivalent homoleptic alkyls and amides, especially of Group 4 elements, and of tin(II) chloride and bromide

Abstract: He(I) photoelectron (pe) spectraof (i) themonomeric, presumed-bent, compounds MR2, M(NR′2)2, and M(NR′R″)2[M = Ge, Sn, or Pb; R = CH(SiMe3)2, R′= SiMe3, and R″= CMe3], (ii) the linear HgR2 and M′(NR′2)2(M = Zn or Hg), and (iii) the bent momomeric SnCl2 and SnBr2 have been recorded, as well as the reference compounds RH, R′2NH, and R′R″NH For the Group 4 metal(II) alkyls the first vertical ionisation potential (ip) is close to that of the free metal; the metal lone-pair orbital is progressively higher in M(NR′R″), and M(NR′2)2, in which compounds it is the second band, being preceded by the antibonding b2 molecular orbital (mo) formed by the nitrogen lone-pair atomic orbitals (aos) Confirmation of this assignment is also provided by comparison of data for the bent and linear metal(II) amides; in the latter, nitrogen lone-pair interactions are negligible Assignments, on the basis of trends and, for MX2, of CNDO calculations, are prooosed and trends noted There is evidence of substantial N→Si pπ–dπ interaction in the amides

Ein gemischt methyl/phenyl-substituiertes Carbodiphosphoran. Darstellung, Reaktionen und verwandte Verbindungen / A Mixed Methyl-/Phenyl-substituted Carbodiphosphorane. Synthesis, Reactions, and Related Compounds

Abstract: From the reaction of bis-diphenylphosphino-methane and methyl bromide a diquaternized onium salt is obtained, which is converted into the carbodiphosphorane MePh₂P=C=PPh₂Me by sodium amide in THF. This bis-ylide was characterized by its reactions and its NMR spectra. With methyl chloride, the above diphosphine yielded the phosphino-phosphonium salt, which forms a phosphino-ylide upon dehydrohalogenation.

Komplexone XLVII. The Stability of Palladium(II) Complexes with Aminopolycarboxylate Anions

Abstract: The formation of Pd(II) complexes with aminopolycarboxylate anions has been investigated using pH and UV.-spectrophotometric measurements at ionic strength 1 M and 20°. In some cases bromide or thiocyanate ions have been used as auxiliary ligands. Pd2+ forms the strongest complexes of the hitherto investigated divalent metal ions. The stability constants are discussed in relation to the particular stereochemistry of Pd(II) complexes.

Field desorption mass spectrometry of phospholipids. II--Fragmentation of dipalmitoylphosphatidyl choline from comparison of d0, d4 and d9 species.

Abstract: Field desorption mass spectra have been obtained for dipalmitoylphosphatidyl choline-d0, -d4 and -d9. The two latter compounds were synthesized from dimethylene-d4 choline bromide and trimethyl-d9 choline bromide, respectively. Comparison was made of spectra of these three compounds obtained at different field anode temperatures in order to establish the composition of the major cleavage, rearrangement, and association ions. At low anode heating currents (less than or equal to 20 mA) the most intense peak is [M + 1]+ which accounts for c. one-third of the total ionization. At higher temperatures various fragmentation processes, some of which are without analogy in electron impact mass spectrometry, become more important. The presence of an intermolecular methyl transfer process had been confirmed.

Molecular motion, phase transitions, and disorder in the pyridinium halides

Abstract: The solid pyridinium chloride, bromide, and iodide salts were studied using 1H nuclear magnetic resonance and differential scanning calorimetry. Phase transitions were observed at 345 K for the chloride, 269 K for the bromide, and 247 K for the iodide. Well below each transition, the pyridinium ions are held rigidly in the crystal lattice, whereas above each transition the ions reorientate rapidly about an axis at right angles to the ring planes. From the temperature dependence of the spin–lattice relaxation times the high temperature phase reorientational activation energies were determined to be 1.55, 2.30, and 4.20 kcal/mol for the chloride, bromide, and iodide, respectively.

On the electrochemical machining of some titanium alloys in bromide electrolytes

Abstract: The current efficiency was determined for the dissolution of a number of titanium alloys (IMI 115, 230, 318 and 550) in a variety of electrolytes based on potassium bromide It was found that these materials in general dissolved at efficiencies somewhat greater than 100% based on the 4-valent dissolution reaction: Ti→Ti4+, although at lower current densities the efficiency was a little lower Using sodium chloride as an additive to the potassium bromide, slight improvements in the stray-current attack properties of the electrolyte and in the surface finish were obtained All the alloys dissolved in the transpassive region of the polarization curve but produced etched surfaces, and evidence is presented to show that the dissolution kinetics is modified by acid generation at the anode and, in the case of the two-phase alloys, also by the occurence of differential dissolution

Organometallic chemistry of the transition metals. XXXI. Stereoisomerism in cyclopentadienylrhenium(III) derivatives

Abstract: Reaction of CsH5Re(CO)3 with bromine in trifluoroacetic acid gives CsH5Re(C0)2Br2 which can be separated into pure diagonal and lateral isomers by column chromatography. The lateral isomer CsHsRe(CO)zBr2 is readily converted to the corresponding diagonal isomer upon mild heating. Reactions of diag-CsHsRe(C0)zBra with the phosphites (RO)3P (R = CH3, C2H5, and CsHs) in boiling benzene give diag-CsHsRe(CO)[P(OR)3]Brz which isomerizes to latCsHsRe(C0) [P(OR)3]Br2 in boiling toluene. The reaction of diag-CsHsRe(C0)2Brz with trimethyl phosphite in boiling toluene also results in methyl bromide elimination to give two isomers of the phosphonate CsHsRe(C0) [P(OCH3)3] [P(O)(OCH3)z]Br. Reaction of diag-CsHsRe(C0)zBrz with tert-butyl isocyanide in boiling benzene gives an isomer of CsHsRe(C0) [ (CH3)3CNC] Br2 which is stable to isomerization in boiling toluene. Simple steric effects are sufficient to explain the stereochemistry of these reactions of cyclopentadienylrhenium(II1) derivatives.

The transport of chloride in Ehrlich ascites tumor cells.

Abstract: The steady state transport and distribution of chloride between the intracellular and extracellular phases was investigated when the extracellular chloride concentration was varied by isosmotic replacement with nitrate, bromide and acetate The results of these experiments show that chloride transport, measured by uptake of 36Cl, is sensitive to the replacement anion In the presence of nitrate, chloride transport is a linear function of the extracellular chloride concentration The relationship between chloride transport and extracellular chloride in the presence of bromide is concave upward which suggests that this anion inhibits chloride movement However, when acetate replaces chloride, the relationship between chloride transport and extracellular chloride is concave downward The chloride distribution ratio of cells incubated in 145–155 mM chloride medium is 0386 and is not effected by the replacement of chloride with nitrate, bromide or acetate These findings are consistent with the assertion that chloride transport is composed of two parallel pathways, a diffusional plus a saturating, mediated component Of the total chloride flux (91 mmoles Cl-/kg dry weight per minute) measured in chloride medium (145–155 mM Cl -), the mediated component represents 40% and the diffusional component 60%

Reactions of .pi.-allylnickel bromide complexes with quinones. Synthesis of isoprenoid quinones

Abstract: Die Reaktion von Allyl-Ni-Komplexen (I) mit Chinon (II) gibt neben den Allylhydrochinonen (III) stets unsubstituiertes Hydrochinon (IV) und das Allyl-dimere (V).

Reactions of D-Glucofuranurono-6,3-Lactone

Abstract: Publisher Summary This chapter discusses the reactions of D-glucofuranurono-6,3-lactone as they have been the subject of extensive investigations. Fundamentally, D-glucofuranurono-6,3-lactone contains the 2,6-dioxabicyclo [3.3.0]octane structure. The chapterdescribes its properties. D-glucofuranurono-6,3-lactone halides exhibit certain properties, such as (1) thermodynamic and solvolytic stability decreases in the series: fluoride, chloride, bromide, (2) 2,5-Di-O-acetyl-D-glucofuranosylurono-6,3-lacton halides are less stable than their 2,5-di-O-benzoyl or their 2-O-acetyl-5-O-benzoyl counterparts, (3) β-D-Glucofuranosylurono-6,3-lactone chlorides are subject to alcoholysis, with formation of alkyl β-D-glucofuranosidurono-6,3-lactones; under the same conditions the α-D-anomers are nonreactive, (4) like methyl 2,3,4-tri-O-acetyl-β-D-glucopyranosyluronate chloride,2,5-di-O-acyl- β-D-glucofuranosylurono-6,3-lactone chloride are quite resistant to anomerization. Furthermore, the reaction of per-O-acylated D-glucosyl bromides and chlorides with alcohols by heterogeneous, or homogeneous, base catalysis is commonly used for the preparation of D-glucosides. By an SN2 type of mechanism under Koenigs-Knorr conditions, α-D-glucopyranosyl halides form β-D-glucopyranosides, which are also obtained from the “unstable” β -D-glucopyranosyl chlorides through neighboring group participation.