The effect of pressure on the dissociation of boric acid and sodium borate ion pairs at 25°C

A high pressure UV-visible spectrophotometer was used to determine the dissociation constant of boric acid using an indicator technique. The measurements were made at 25°C and at ionic strengths of 0.1 and 1.0m over a pressure range of 1 to 2000 atm. Extrapolation to I=0 gave a thermodynamic dissociation constant of 5.16×10^–10 at 1 atm. The pressure dependence yielded a partial molal volume change of –28.9 and –31.8 cm³-mol^–1 and a compressibility change of –3.1 and –4.8×10^–3 cm³-mol^–1-atm^–1 for the dissociation at I=0.1 and 1.0m, respectively. The association constant for the formation of the sodium borate ion pair was determined by comparing the acid constants in tetramethylammonium chloride to those in sodium chloride solutions. Extrapolation to I=0 yielded a K_A for [NaB(OH)₄] of 0.64 at 1 atm. The pressure dependence of K_A gave and for the formation of the ion pair.     

Group additivity for the standard partial molal heat capacities and volumes of polar compounds in methanol at 25°C

A flow heat capcity calorimeter and a flow vibrating tube densimeter have been used to measure the apparent molal heat capacities and volumes of benzene and 25 polar compounds in methanol at 25°C. These quantities have been extrapolated to infinite dilution to obtain the standard partial molal heat capacities and volumes. The and data have been used in conjunction with an additivity scheme previously determined for alkanes. Group contributions were evaluatd for –OH, –NH₂, –COOH, –C₆H₅, C=O, –COO–, –CONH–, –O–, –S–, and –S₂–. The concentration dependences of _cp and _v of nonelectrolytes in methanol are qualitatively similar but much smaller than in water.     

Hydrolysis constants and ion-interaction parameters for Cd(II) in zero to high concentrations of NaOH−KOH,and the solubility product of crystalline Cd(OH)2

The solubility of Cd(OH)₂(c) was studied in 0.01M NaClO₄ solutions, from both the over- and the undersaturation directions, with OH^– ion concentration ranging from 10^–6 to 1.0 mol-L^–1, and the equilibration period ranging from 2 to 28 days. Equilibrium Cd concentrations were reached in less than 2 days. The Cd(OH)₂(c) solubility showed an amphoteric behavior. In the entire range of OH^–/H⁺ investigated, the only dominant aqueous Cd(II) species required to explain the solubility of Cd(OH)₂(c) are Cd²⁺, Cd(OH) ₂ ⁰ , and Cd(OH) ₄ ^2– . The logarithms of the thermodynamic equilibrium constants of the Cd(OH)₂(c) solubility reactions involving these species, that is, the reactions

Dissociation Constants of Protonated Cysteine Species in NaCl Media

The sulfur-containing biomolecule, cysteine has a role in physiological and natural environment because of its strong interactions with metals. To understand these interactions of metals with cysteine, one needs reliable dissociation constants for the protonated cysteine species [ CH(CH₂SH)COOH; H₃B⁺]. The values of dissociated constants, p , for protonated cysteine species (H₃B⁺ H⁺ + H₂B, K ₁; H₂B H⁺ + HB^–,K ₂; HB^– H⁺ + B^2–,K ₃) were determined from potentiometric measurements in NaCl solutions as a function of ionic strength, 0.5–6.0 mol-(kgH₂O)^–1 and between 5, and 45°C. The equations

Magnetite solubility and phase stability in alkaline media at elevated temperatures

A platinum-lined flowing autocláve facility was used to investigate the solubility behavior of magnetite (Fe₃O₄) in alkaline sodium phosphate and ammonium hydroxide solutions between 21 and 288°C. Measured iron solubilities were interpreted via a Fe(II)/Fe(III) ion hydroxo-, phosphato-, and ammino-complexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A total of 14 iron ion species were fitted. Complexing equilibria are reported for 8 new species: Fe(OH)(HPO₄)^–, Fe(OH)₂(HPO₄)^2–, Fe(OH)₃(HPO₄)^2–, Fe(OH)(NH₃)⁺, Fe(OH)₂(PO₄)^3–, Fe(OH)₄(HPO₄)^3–, Fe(OH)₂(H₂PO₄)^–, and Fe(OH)₃(H₂PO₄)^3–. At elevated temperatures, hydrolysis and phosphato complexing tended to stabilize Fe(III) relative to Fe(II), as evidenced by free energy changes fitted to the oxidation reactions.

Dissociation Constants for Citric Acid in NaCl and KCl Solutions and their Mixtures at 25 °C

The constants for the dissociation of citric acid (H₃C) have been determined from potentiometric titrations in aqueous NaCl and KCl solutions and their mixtures as a function of ionic strength (0.05–4.5 mol-dm^–3) at 25 °C. The stoichiometric dissociation constants (K_i^*)

Photochemical reactions of radical-anionsH_2 S_{\bar 2}^ \cdot in solid phasein solid phase

Photochemical reactions of radical-anions with incident light of 405 and 365 nm were studied quantitatively in matrices of 6M LiCl, 4M CH₃COONa, and C₂H₅OH. the radical-anions were shown to undergo reaction of S–S and S–H bond dissociation. Relative efficiency of the observed processes depends on the energy of incident light, on the nature of matrix, and on the degree of self-association of hydrogen sulphide.     

Apparent molal heat capacities of organic solutes in water. V. aminoalcohols,aminoethers, diamines,and polyethers

Apparent molal heat capacities of 20 organic uncharged compounds in aqueous solution have been determined at 25 and 40°C. The substances studied include mono- and polyfunctional ethers, and bifunctional open-chain compounds like aminoalcohols, aminoethers, and diamines. The results obtained support the presence of interaction between water and the hydrophilic groups –O–, –NH₂, –NH–, and , and evidence indicates that these interactions strongly depend on the molecular structure of the compound containing the functional group.     

Ion-molecular interactions in the HCl—isopropanol system

Multiple Attenuated Total Reflectance (MATR) IR spectra of solutions of HCl in isopropanol, containing 0 to 43 mol. % HCl, were studied in the 900–4000 cm^–1 range. The addition of HCl to PrⁱOH yields proton disolvates with strong symmetrical H-bonds. At high concentrations of HCl (C _HCl ⁰ > 5.7 mol L^–1, /C⁰ _HCl < 2), when the number of alcohol molecules is not enough to form disolvates with all of the protons present in the solution, (Cl...H...Cl)^– ions are formed, in addition to (C₃H₇OH)₂H⁺. The spectra of these ions have been assigned.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1753–1756, September, 1995.This work was carried out with financial support of the Russian Foundation for Basic Research (Project No. 93-03-18356).     

The first ionization constant from 25 to 200°C and 2000 bar for orthophosphoric acid

The ionization constant of orthophosphoric acid, determined by conductivity measurements, decreased from 7.11×10^–3 at 25°C to 6.2×10^–4 mol-kg^–1 at 200°C. The pressure effect to 2000 bar was also measured and the ratio K₂₀₀₀/K₁ is 2.7 at 25°C and 3.7 at 200°C. The standard partial molar volume change for the ionization at 1 bar, , changes from –16.1 at 25°C to –33.3 cm³-mol^–1 at 200°C. The partial molar compressibility change for the ionization, , varies from –3.8×10^–3 to –8.3×10^–3 cm³-mol^–1 bar^–1 over the same temperature range.     

O-H ... O(S) hydrogen bonds in 2-hydroxy(thio)benzamides. Survey of spectroscopic and structural data

Summary From a survey of spectroscopic and structural data of six corresponding 2-hydroxybenzamides and 2-hydroxythiobenzamides (amide, N-methylamide, N,N-dimethylamide, piperidide, morpholide, 2,6-dimethylpiperidide) remarkable similarities between O(N)-H ... O and O(N)-H ... S hydrogen-bonds are obtained, concerning both, hydrogen-bond patterns and hydrogen-bond strengths. In dilute solution the OH groups of all compounds are intramolecularly associated to the (thio)carbonyl O (S) atoms with distinctly larger hydrogen-bond strengths for primary and secondary amides [ (O-H)=2950–3020 cm^–1, (OH)=12.16–11.99 ppm] and thioamides [ (O-H)=2960–3000 cm^–1, (OH)=11.65–11.13 ppm], than for tertiary amides [ (O-H)=3200–3250 cm^–1, (OH)=9.95–8.95 ppm] and thioamides [ (O-H)=3245–3330 cm^–1, (OH)=8.09–7.06 ppm]. In the solid state, the OH groups of the primary and secondary (thio)amides are also engaged in rather strong intramolecular O-H ... O=C [O ... O=2.51 Å, (O-H)=2700–2750 cm^–1] and O-H ... S=C [O ... S=2.90–2.94 Å, (O-H)=2700–2840 cm^–1] hydrogen-bonds; thetrans-NH groups of the primary (thio)amides and the NH groups of the secondary (thio)amides connect the molecules to N-H ... O-H [N ... O=2.93–3.10 Å, (N-H)=3319–3407 cm^–1] hydrogen-bonded chains; the remainingcis-NH groups of the primary (thio)amides give rise to eight-membered cyclic dimers via N-H ... O=C [N ... O=2.93 Å, (N-H)=3226 cm^–1] and N-H ... S=C [N ... S=3.46–3.47 Å, (N-H)=3233–3277 cm^–1] hydrogen-bonds. Contrary, the OH groups of the tertiary (thio)amides are intermolecular associated in the solid state and link the molecules to O-H ... O=C [O ... O=2.63–2.75 Å, (O-H)=3075–3135 cm^–1] and O-H ... S=C [O ... S=3.18–3.26 Å, (O-H)=3130–3190 cm^–1] hydrogen-bonded chains.

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O-H ... O(S)-Wasserstoffbrückenbindungen in 2-Hydroxy(thio)benzamiden. Ein Überblick über spektroskopische und strukturelle Daten

Zusammenfassung Aus einer Zusammenstellung von spektroskopischen und strukturellen Daten von sechs entsprechenden 2-Hydroxybenzamiden und 2-Hydroxythiobenzamiden (Amid, N-Methylamid, N,N-Dimethylamid, Piperidid, Morpholid, 2,6-Dimethylpiperidid) ergeben sich bemerkenswerte Analogien zwischen O(N)-H ... O und O(N)-H ... S H-Brücken, die sowohl die H-Brücken-Muster als auch die H-Brücken-Stärken betreffen. In verdünnter Lösung sind die OH-Gruppen aller Verbindungen intramolekular mit den O(S)-Atomen der (Thio)Carbonylgruppen assoziiert, wobei die H-Brücken bei den primären und sekundären Amiden [ (O-H)=2950–3020 cm^–1, (OH)=12.16–11.99 ppm] und Thioamiden [ (O-H)=2960–3060 cm^–1, (OH)=11.65–11.13 ppm] deutlich stärker sind, als bei den tertiären Amiden [ (O-H)=3200–3250 cm^–1, (OH)=9.95–8.95 ppm] und Thioamiden [ (O-H)=3245–3330 cm^–1, (OH)=8.09–7.06 ppm]. Im Festkörper weisen die primären und sekundären (Thio)Amide ebenfalls sehr starke intramolekulare O-H ... O=C [O ... O=2.51 Å, (O-H)=2700–2750 cm^–1] und O-H ... S=C [O ... S=2.90–2.94 Å, (O-H)=2700–2840 cm^–1] H-Brücken auf; dietrans-NH-Gruppen der primären (Thio)Amide und die NH-Gruppen der sekundären (Thio)Amide verknüpfen die Moleküle über N-H ... O-H H-Brücken [N ... O=2.93–3.10 Å, (N-H)=3318–3407 cm^–1] zu Ketten; die verbleibendencis-NH-Gruppen der primären (Thio)Amide bilden zyklische, über N-H ... O=C [N ... O=2.93 Å, (N-H)=3226 cm^–1] und N-H ... S=C [N ... S=3.46–3.47 Å, (N-H)=3233–3277 cm^–1] H-Brücken gebundene, 8-Ring-Dimere. Im Gegensatz dazu sind die OH-Gruppen der tertiären (Thio)Amide im Festkörper intermolekular assoziiert und verknüpfen die Moleküle über O-H ... O=C [O ... O=2.63–2.75 Å, (O-H)=3075–3135 cm^–1] und O-H ... S=C [O ... S=3.18–3.26 Å, (O-H)=3130–3190 cm^–1] H-Brücken zu Ketten.

     

An evaluation of rate constants for radiation induced decomposition of alkali metal nitrates

Radiation induced decomposition of solid alkali metal nitrates at room temperature has been studied up to an absorbed dose of 300 kGy. [NO ₂ ^– ] increases with absorbed dose. From the kinetic scheme and , rate constants have been evaluated for the overall radiolytic decomposition of alkali metal nitrates. This kinetic scheme is applicable in the low dose range. At higher doses, however, the radiation induced reaction, NO ₂ ^– +1/2 O₂NO ₃ ^– may also contribute. The overall rate constants are 0.13×10^–6 (LiNO₃), 1.05×10^–6 (NaNO₃), 10.10×10^–6 (KNO₃), 9.50×10^–6 (RbNO₃) and 25.50×10^–6 (CsNO₃) kGy^–1.     

Thermodynamic Properties of Alanylpeptide Buffer Systems and Their Potential as Standards in Biological Applications

The second dissociation constants pK ₂of the NH₃ ⁺charge center of the alanylpeptides, alanylglutamine (Ala–Gln), alanylleucine (Ala–Leu), alanylglycine (Ala–Gly), and DL-alanyl–DL-methionine (DL-Ala–DL-Met) were determined at ten temperatures in the range, 5–50°C. These pK ₂values were calculated from the emf of cells containing buffer solutions of these dipeptides. A cell of the type described by Harned and Ehlers,⁽¹⁾utilizing hydrogen and silver–silver bromide electrodes was used. The thermodynamic quantities, H^o, S^o, and C_p ^owere derived from the temperature coefficients of the dissociation constants. The pK ₂values at 25°C, 8.2105 ( Ala–Gln), 8.2668 ( Ala–Leu), 8.2940 ( Ala–Gly), and 8.3054 ( DL-Ala–DL-Met). These values show that different substituent groups on the -carbon atom (which include polar and nonpolar groups), have a small effect on the dissociation of the NH₃ ⁺charge center. These compounds were also found to be suitable as buffers in the pH range(7–9). The thermodynamics of the solute–solvent interaction is interpreted in terms of the mixture model.⁽²⁾     

Mass transfer in shell-core inorganic TIP1 ion exchanger

The ion exchange processes of (OAc^–) and (OAc^–) proceeding in shell-core inorganic ion exchanger Ti (HPO₄)₂·1/2H₂O has been studied and the diffusion equation whose boundary conditions are satisfied by a shell-core model was solved. Based on the equation solved and experimental data, the diffusion coefficients corresponding to the exchange process (OAc^–) and Li⁺–H⁺ (OAc^–) at 17°C are found to be 7.7×10^–9 and 6.2×10^–8 cm² s^–1 and the activation energies 3.4×10⁴ and 5.0×10³ J mol^–1, respectively. Compared to the gel type of styrene-divinylbenzene strong acid exchanger with 20% cross linking, it can be concluded that the rate of or exchange is 3.5 times faster than that in the organic exchanger.TIP was obtained from the Salt Lake Institute of the Academy of Science of China.     

The partial molal volume and compressibility change for the formation of the calcium sulfate ion pair at 25°C

The apparent molal volumes (_v) and compressibilities (_K) of CaSO₄ solutions have been determined at 25°C from precise density and sound-speed measurements. The large deviations of the values of _v and _K from the limiting law and various additivity estimates for the free ions (Ca²⁺, SO ₄ ^2– ) have been used to estimate the partial molal volume ( ) and compressibility ( ) for the formation of the CaSO ₄ ⁰ ion pair. Values of = 25 ± 3 cm³-mole^–1 and = (54±21)×10^–4 cm³-mole^–1-bar^–1 were found. Since these values are larger than the value for the formation of MgSO ₄ ⁰ , the results indicate that more inner-sphere ion pairs are formed when SO ₄ ^2– complexes with Ca²⁺ than with Mg²⁺. Using a simple model for ion-water interactions, the percent of inner-sphere or contact ion pairs in CaSO₄ solutions is estimated to be 36 to 37%.     

Hydrogen bonding in 2-hydroxy-benzhydrazide and 2-hydroxy-thiobenzhydrazide. Structural and spectroscopic study

Summary X-ray structural data are reported for 2-hydroxy-benzhydrazide(monoclinic; P2₁/n-C _2h ⁵ ;a=10.569(2) Å,b=11.264(2) Å,c=6.074(1) Å, =98.80(1)°;Z=4;R=0.054) and 2-hydroxy-thiobenzhydrazide (monoclinic; P2₁/n-C _2h ⁵ ;a=14.598(6) Å,b=5.975(2) Å,c=9.286(4) Å, =107.80(3)°;Z=4;R=0.044). In both compounds the phenolic OH groups are intramolecularly hydrogen bonded to the (thio)carbonyl oxygens and sulfurs, respectively; the basic intermolecular association patterns consist of closed six-membered hydrogen bonded dimers which are connected via N-H ... NH₂ hydrogen bonds. The spectral characteristics of the intramolecular O-H...O/S hydrogen bonds (solid state (OH)=2800/2700 cm^–1, CCl₄ solution (OH)=3035/3100 cm^–1, CDCl₃ solution (OH)=11.62/10.56 ppm) are similar to those of corresponding primary and secondary amides. The solid state IR spectra are consistent with hydrogen bonded NH groups and free NH₂ groups, the solution IR spectra indicate free NH₂ as well as free NH groups.

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Wasserstoffbrückenbindung in 2-Hydroxy-benzhydrazid und 2-Hydroxy-thiobenzhydrazid. Strukturelle und spektroskopische Untersuchungen

Zusammenfassung Es werden Röntgenstrukturdaten für 2-Hydroxy-benzhydrazid (monoklin; P2₁/n- C _2h ⁵ ;a=10.569(2) Å,b=11.264(2)Å,c=6.074(1)Å, =98.80(1)°;Z=4;R=0.054) und 2-Hydroxy-thiobenzhydrazid (monoklin; P2₁/n - C _2h ⁵ ;a=14.598(6)Å,b=5.975(2)Å,c=9.286(4)Å, =107.80(3)°;Z=4;R=0.044) berichtet. In beiden Verbindungen bilden die phenolischen OH-Gruppen intramolekulare Wasserstoffbrücken mit den Carbonyl-Sauerstoff-, bzw. den Thiocarbonyl-Schwefel-Atomen. Das intermolekulare Assoziationsmuster wird durch N-H...NH₂ Wasserstoffbrücken bestimmt, die jeweils zwei Moleküle über sechszählige Ringe zu Dimeren verbinden. Die IR- und NMR-spektroskopischen Charakteristika der intramolekularen O-H...O/S Wasserstoffbrücken (kristallin: (OH)=2800/2700 cm^–1, CCl₄-Lösungen: (OH)=3035/3100 cm^–1, CDCl₃-Lösungen: (OH)=11.62/10.56 ppm) sind sehr ähnlich zu denen entsprechender primärer und sekundärer Amide. Die Festkörper-IR-Spektren stehen in Einklang mit assoziierten NH- und freien NH₂-Gruppen, während die Lösungs-IR-Spektren auch auf das Vorliegen freier NH-Gruppen schließen lassen.

     

The volume and compressibility change for the formation of transition metal sulfate ion pairs at 25°C

The apparent molal volume and adiabatic compressibilities of some transition metal (Mn²⁺, Co²⁺ Ni²⁺, Cu²⁺, Zn²⁺, and Cd²⁺) sulfates have been determined at 25°C. Values of to 11.4 cm³-mole^–1 and to 31.3 × 10^–4cm³-mole^–1-bar^–1 at 1 atm were found for the formation of the transition metal sulfate ion pairs. These results are in good agreement with the values obtained from the high-pressure conductance measurements of Fisher et al., Shimizu et al., and Taniguchi et al. The volume and compressibility data indicate that 3.1±0.7 water molecules are lost when transition metals form ion pairs with SO ₄ ^2– . The fractions of inner-sphere ion pairs (20%) estimated in this study are in good agreement with the values obtained from ultrasonic measurements.     

Radiolysis of p-benzoquinone solutions

The products of the continuous radiolysis of p-benzoquinone (Q) at different concentrations of H₂SO₄, Q and Cl^– are p-hydroquinone (H₂Q) and 2-hydroxy-p-benzoquinone (2-Q-OH). In the presence of some alcohols, a carbonyl compound is produced in addition to H₂Q and 2-Q-OH. The dependence of G values of the products on these factors is described. The material balance between G(-Q) and G(H₂Q)+G(2-Q-OH) is maintained. The experimental results indicate the occurrence of the following reaction: . By competition studies, it was possible to evaluate the rate coefficients for the following reactions: .     

Kinetics and mechanism of oxidation of hydroxylamine by tetrachloroaurate(III) ion

The oxidation of H₂NOH is first-order both in [NH₃OH⁺] and [AuCl₄ ^–]. The rate is increased by the increase in [Cl^–] and decreased with increase in [H⁺]. The stoichiometry ratio, [NH₃OH⁺]/[AuCl₄ ^–], is 1. The mechanism consists of the following reactions.