Calculation of the thermodynamic characteristics of ions in vapor over sodium fluoride

The geometric parameters, normal vibration frequencies, and thermochemical characteristics of the ions present in vapor over sodium fluoride, Na₂F⁺, Na₃F ₂ ⁺ , NaF ₂ ^? , and Na₂F ₃ ^? , were calculated ab initio by the Hartree-Fock method and taking into account electron correlation. The main equilibrium configuration of all ions was found to be the linear configuration of D _∞h symmetry. Pentaatomic ions could also exist as two isomers, planar cyclic of C _2v symmetry and bipyramidal of D _3h symmetry. Their energies were higher than that of the D _∞h isomers, and their contents in vapor were negligibly low. The energies and enthalpies of dissociation of the ions with the elimination of the NaF molecule were calculated. The enthalpies of formation of the ions were obtained.     

Structural and thermodynamic characteristics of amide solvents

The structural and thermodynamic characteristics of amide solvents are calculated with different types of molecular self-assembly through hydrogen bonding. Under a model-based approach, the specific and nonspecific components of the total energy of intermolecular interactions are identified for primary, secondary, and tertiary amides of carboxylic acids. It is found that similarly to water, primary amides have a network of hydrogen bonds and belong to the class of liquids characterized by an increase in nonspecific interactions with temperature. In secondary amides with the chain self-assembly, the contribution of these interactions is practically independent of temperature, and in tertiary amides it decreases with an increase in temperature. The molar values of the specific and nonspecific components are used to analyze the intermolecular interactions and the structural properties of amides with different degrees of N-substitution.     

The thermodynamic properties and solvation of ammonium bromide,iodide, and nitrate in methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of ammonium bromide, iodide, and nitrate in methylpyrrolidone (MP) were studied calorimetrically and densimetrically at 298.15 K. The standard partial molar heat capacities and volumes (\(\overline {C_{p_2 }^O } \) and \(\overline {V_2^O } \)) of the electrolytes in MP were calculated. The standard heat capacities \(\overline {C_{p_i }^O } \) and volumes \(\overline {V_i^O } \) of the nitrate and ammonium ions in MP were determined. The mean coordination numbers of the NH ₄ ⁺ and NO ₃ ^? ions in a solution in MP at 298.15 K were calculated.     

Analysis of thermodynamic characteristics of imidazolium-based ionic liquid on coal

To investigate the effects of ionic liquids (ILs) on the oxidative combustion characteristics of coal, the oxidation characteristics of ILs on coal, such as characteristic temperature, thermal mass loss rate, and oxidation kinetics characteristic parameters, were determined. The results the [BMIm][I]-treated coal samples increased cracking temperature (T₁), maximum oxidization mass gain (T₂), ignition temperature (T₃), burnout temperature (T₄), minimum thermal rate (T_a), maximum thermal energy (T_b), and maximum thermal rate (T_c) by 33.2, 29.3, 20.7, 42.8, 11.4, 23.0, and 27.9 °C, respectively. The increase mass ratio of coal samples treated with ILs increased and decreased at the water evaporation and thermal decomposition stages, respectively. The apparent activation energy (E_a) of coal samples treated with ILs increased, and the mechanism function also changed accordingly. These showed that the ILs improved the thermal stability of the coal samples in the stages of absorbing oxygen and increased mass, and the loss of combustion. The ILs caused damage to the molecular structure of the coal and ultimately effected changes in the combustion performance. In addition, the [BMIm][BF₄] hardly weakens the inhibitory effectiveness of the coal sample over time; coal spontaneous combustion could be effectively inhibited.

     

Structural thermodynamic characteristics and intermolecular interactions in aqueous solutions of hexamethylphosphorotriamide

Structural thermodynamic parameters of aqueous solutions of hexamethylphosphorotriamide are calculated. They are discussed together with previously obtained data on aqueous solutions of disubstituted amides of carboxylic acids. The specific and non-specific components of the total energy of intermolecular interactions are determined. The boundaries of concentration regions with different structural organizations of solutions are found, and the preferential solvation parameters of solution components are estimated.     

Structural and thermodynamic aspects of ionic solvation in concentrated aqueous poly(ethylene glycol)

Solvation of ions in concentrated aqueous poly(ethylene glycol) (PEG) has been studied from thermodynamic and structural viewpoints using ion-transfer voltammetry at the interface between aqueous and nitrobenzene phases and X-ray absorption fine structure (XAFS). Systematic changes in the ion-transfer potential from water to aqueous PEG have been confirmed for several ions relative to the corresponding potential of tetraethylammonium ion (Et4N+), which is almost independent of PEG concentration. The results obtained for alkali cations strongly suggest the involvement of their complexation with PEG even in relatively diluted PEG solutions. It has been implied that the solvation circumstances of Br- and ClO4- are drastically altered when the PEG concentration becomes higher than particular critical values (e.g., 30-50% PEG200), where free water molecules are diminished because of the hydration of PEG. XAFS measurements have also been performed for K+ and Br- to get direct evidence for these findings. Although the spectra at the K K-edge clearly indicate the presence of a PEG complex of K+ in relatively diluted PEG solutions ( approximately 33% PEG200), an obvious increase in its ion-transfer potential has been detected at lower PEG concentrations, indicating that complexes formed at the interface rather than in bulk solution are transferred into an organic phase. Br- is fully hydrated in 0-50% PEG solutions, whereas some water molecules are replaced by PEG when the PEG concentration increases. Increasing the PEG concentration causes decreases in the coordination number from 6 in water to 2-3 in neat PEG. Thus, the present approach not only has elucidated the structural and thermodynamic aspects of ionic solvation in aqueous PEG but also has provided the information of the hydration of PEG.     

Composition of lithium and sodium metaborate vapors

Journal of Structural Chemistry -     

Structural and thermodynamic characteristics of dilute solutions of alcohols in aprotic solvents

The enthalpies of H-bonds in ethanol and isopropanol complexes with aprotic solvents, extractants of aromatic hydrocarbons, were determined. The thermodynamic functions of viscous flow activation and the mean degrees of association in dilute solutions of the alcohols in N-methylpyrrolidone, dimethylsulfoxide, and tetramethylenesulfone were obtained. The roles played by the energy and steric effects in the solution of alcohols in the solvents were estimated.     

Thermodynamic characteristics of ionic association in dimethylformamide solutions of barium iodide and zinc and lantane chlorides

Enthalpies of electrolyte transfer and differences between enthalpies of anions transfer from water to mixed solvent were defined on the basis of results from our own measurements of dissolution enthalpies of potassium acetate in mixed solvents acetonitrile-water and dimethylformamide-water of different composition, and of the literature data on dissolution enthalpies of other electrolytes in the same mixed solvents. These values are discussed with the aim of establishing the principles of solvatation for different anions in the studied mixed solvents.     

Specific adsorption of bromide and iodide ions from N-methyl formamide solutions with constant ionic strength on liquid ga electrode

The differential capacitance curves were measured with an ac bridge in the Ga/[N-MF + 0.1 m M KBr + 0.1 (1 − m) M KClO₄] and Ga/[N-MF + 0.1 m M KI + 0.1 (1 − m) M KClO₄] systems at the following fractions m of surface-active anions: 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1. As compared with other solvents, N-methyl formamide (N-MF) enables one to realize the largest positive charges of Ga electrode, at which it remains ideally polarizable (up to 20 μ/cm²). The data on the specific adsorption of Br⁻ and I⁻ anions in the system can be quantitatively described by the Frumkin’s isotherm; to the first approximation, free energy of halide ion (Hal⁻) adsorption DG_{adsHal ^{- 1}} \Delta G_{adsHal^{ - 1} } is a linear function of electrode charge. It is found that, in contrast to the Hg/N-MF interface, DG_{adsHal ^{- 1}} \Delta G_{adsHal^{ - 1} } at the Ga/N-MF interface varies in the reverse order: Br^t— ∼ I⁻ < Cl⁻. From the measured results, we can conclude that the energy of metal-Hal⁻ interaction increases in series: $\Delta G_{M - Cl^ - } > \Delta G_{M - Br^ - } > \Delta G_{M - I^ - } $\Delta G_{M - Cl^ - } > \Delta G_{M - Br^ - } > \Delta G_{M - I^ - } and the difference (DG_{Ga - Hal1^-} - DG_{Ga - Hal2^-} )(\Delta G_{Ga - Hal_1^ - } - \Delta G_{Ga - Hal_2^ - } ) is larger than the difference between the solvation energies of Hal^- (DG_{S - Hal1^-} - DG_{S - Hal2^-} )Hal^ - (\Delta G_{S - Hal_1^ - } - \Delta G_{S - Hal_2^ - } ).     

Structural and thermodynamic features of complexes formed by DNA and synthetic polynucleotides with dodecylamine and dodecyltrimethylammonium bromide

Complex formation of native and denatured DNA, single-stranded polyribonucleotides poly(A) and poly(U), as well as double-stranded poly(A).poly(U) with dodecylamine (DDA) and dodecyltrimethylammonium bromide (DTAB) has been studied by UV-, CD-, IR-spectroscopy and fluorescence analysis of hydrophobic probe pyrene. DDA and DTAB were shown to bind cooperatively with DNA and polyribonucleotides, resulting in the formation of complexes containing hydrophobic micelle-like clusters. Critical aggregation concentration (CAC) of DDA and DTAB shifts sharply to lower values (30-50 times) in the presence of DNA and polynucleotides as compared to critical micelle concentration (CMC) of free DDA and DTAB in solution. The analysis of binding isotherms within the frame of the model of cooperative binding of low-molecular ligands to linear polymers allowed us to determine the thermodynamic parameters of complex formation and estimate the contribution of electrostatic interaction of positively charged heads of amphiphiles with negatively charged phosphate groups of DNA and polyribonucleotides, and hydrophobic interaction of aliphatic chains to complex stability. Electrostatic interaction was shown to make the main contribution to the stability of DNA complexes with DDA, while preferential contribution of hydrophobic interactions is characteristic of DTAB complexes with DNA. The opposite effect of DDA and DTAB on the thermal stability of DNA double helix was demonstrated from UV-melting of DNA-while DTAB stabilizes the DNA helix, DDA, to the contrary, destabilizes it. The destabilizing effect of DDA seems to originate from the displacement of intramolecular hydrogen bonds in complementary Watson-Crick A.T and G.C base pairs with intermolecular H-bonds between unsubstituted DDA amino groups and proton-accepting sites of nucleic bases.     

Nanoscale heterogeneity in alkyl-methylimidazolium bromide ionic liquids

High-energy x-ray diffraction measurements and atomistic molecular dynamics (AMD) numerical simulations have been carried out on 1-alkyl-3-methylimidazolium bromide ionic liquids, C(n)mimBr, with n = 2, 4, and 6. Excellent agreement between experiment and simulation is obtained, including the region of the low-Q peak that has proved problematic in previous work in the literature. In the partial structure analysis of the AMD results, a distinct peak develops at the leading edge of the ring-ring pair distribution function and shifts to lower r with increasing alkyl chain length, indicating that the preferential parallel and antiparallel alignment of neighboring cation rings plays a larger role with increasing chain length. The ring-ring, anion-anion, and ring-anion partial structure factors are dominated by strong charge-ordering peaks around 1.1 A?(-1), corresponding to a distance between neighboring polar entities of D(2) = 5.7 A?. In contrast, the tail-tail S(Q) is dominated by the low-Q peak that rises and moves to lower Q with increasing chain length; the length scale of this structural heterogeneity D(1) increases from about 10 A? in C(2)mimBr to 14.3 A? in C(4)mimBr and 18.8 A? in C(6)mimBr. Both the length scale of the structural heterogeneity and its anomalous temperature dependence in the C(n)mimBr liquids studied here show considerable similarity to results in the literature for C(n)mimPF(6) liquids, indicating a remarkable insensitivity to the form and size of the anion. Our results are consistent with the concept of nanoscale heterogeneity with small, crystal-like moieties.     

Determination of nitrite and mixtures of bromide and iodide with o-iodosobenzoate

Nitrite diazotizes sulphanilamide, which then does not undergo 3,5-dibromination. Nitrite can therefore be determined by reaction with excess of sulphanilamide, the surplus of which is then titrated with o-iodosobenzoate or chloramine-T in the presence of potassium bromide, with Methyl Red as indicator. Mixtures of iodide and bromide can be analysed by oxidation of the iodide with excess of o-iodosobenzoate at pH 4-6, followed by extraction of the iodine (which is then titrated with thiosulphate) and then oxidation of the bromide in dilute sulphuric acid medium in the presence of sulphanilamide as bromine scavenger, the residual oxidant being evaluated iodometrically.     

Formation of ionic associates by Phenol Red and their interaction with ionic surfactants in aqueous solutions

Formation of associates between single-or double-charged anions of sulfophthalein dye Phenol Red and single-charged cations of cyanines in aqueous solutions was considered. The association constants were estimated from the spectral data. Geometric and energy characteristics of the associates were calculated. The suitability of the associates formed by Phenol Red for quantitative determination of cationic surfactants in aqueous solutions was examined.     

Palladium-catalyzed carbohalogenation: bromide to iodide exchange and domino processes

Aryl bromides have been used to prepare a variety of nitrogen- and oxygen-containing heterocycles featuring new carbon-carbon and carbon-iodine bonds. This palladium-catalyzed carbohalogenation requires potassium iodide for the reaction to proceed in high yields. Additionally, the first examples of domino carbohalogenation reactions have been demonstrated using both aryl iodide and aryl bromide starting materials. Complex products with multiple rings and stereogenic centers are generated in excellent yields with moderate to excellent diastereoselectivities.     

The enthalpimetric determination of mixtures of chloride,bromide and iodide

The individual components of mixtures of chloride (0–1 mmol), bromide and iodide (0–0.1 mmol) may be determined by the use of direct injection enthalpimetry. The heats of reaction of the ions with various reagents have been shown to be additive and the use of non-selective reagents is thus made possible. The amounts of the halides present are calculated by simultaneous equations. The limits of the methods are discussed.     

Selective determination of bromide and iodide in serum and urine by gas chromatography

A gas chromatographie method with electron capture detection is described for the simultaneous determination of bromide and iodide in biological matrices such as serum and urine. Samples are purified by passing them through a disposable C-18 reversed phase silica cartridge; bromide and iodide are derivatized in acid medium to 2-bromoethanol and 2-iodoethanol by ethylene oxide and the derivatives are extraced into ethyl acetate. Detection limits are in the low ng/ml-range.