Comparison of temperature,pressure and isotope effects on the proton jump between the hydroxide and oxonium ion

The limiting molar conductances ° of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD^– (OH^–) and a D₃O⁺ (H₃O⁺) ion. The excess conductances of the OD^– ion in D₂O and the OH^– ion in H₂O, _E ⁰ (OD^-) and _E ⁰ (OH^-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances, _E ⁰ (D⁺) and _E ⁰ (H⁺). However, the temperature effect on the excess conductance is larger for the OD^–(OH^–) ion than for the D₃O⁺ (H₃O⁺) ion but the pressure effect is much smaller for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD^– (OH^–) ion than for the D₃O⁺ (H₃O⁺) ion. Concerning the isotope effect, the value of _E ⁰ (OH^-)/ _E ⁰ (OD^-) deviates considerably from at each temperature and pressure in contrast with that of _E ⁰ (H⁺)/ _E ⁰ (D⁺), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD^– (OH^–) or the D₃O⁺ (H₃O⁺) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D₂O and H₂O, and their variations with temperature, pressure, and isotope.     

Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

The limiting molar conductances Λ⁰ of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH^? (OD^?) and a H₃O⁺ (D₃O⁺) ion. The excess conductance of the OD^? ion in D₂O λ _E ^O (OD ^-), as estimated by the equation $$\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)$$ increases a little with pressure as well as the excess conductance of the OH^? ion in H₂O $$\lambda _E^O (OH^ - ) = \Lambda ^O (KOH/H_2 O) - \Lambda ^O (KCl/H_2 O)$$ However, their rates of increase with pressure are much smaller than those of the excess deuteron and proton conductances, λ _E ^O (D ⁺) and λ _E ^O (H ⁺). With respect to the isotope effect on the excess conductance, λ _E ^O (OH ^-)/λ _E ^O (D ⁺) decreases with presure as in the case of λ _E ^O (H ⁺)/λ _E ^O (D ⁺), but the value of λ _E ^O (OH ^-)/λ _E ^O (OD ^-) itself is much larger than that of λ _E ^O (H ⁺)/λ _E ^O (D ⁺) at each pressure. These results are ascribed to the difference in the pre-rotation of water molecules, which is brought about by the difference in the intial orientation of the rotating water molecule adjacent to the OH^? (OD^?) or the H₃O⁺ (D₃O⁺) ion.     

Conductivity Studies of <Emphasis Type="Italic">n</Emphasis>-Tetrabutylammonium Tetraphenylborate in 3-Pentanone in the Temperature Range from 283.15 to 329.15 K

The molar conductivities (Λ) of solutions of n-tetrabutylammonium tetraphenylborate (NBu₄BPh₄) in 3-pentanone have been measured in the temperature range from 283.15 to 329.15 K. The conductance data have been analyzed using the Lee-Wheaton conductivity equation with the distance parameter (a) set at Bjerrum’s pairing distance, and the limiting molar conductivities (Λ_o) and the association equilibrium constants (K _A) have been derived. The limiting ion conductivities (λ_±^o) have been evaluated according to the method of Krumgalz. The λ₊ ^o values have been compared with λ₊ ^o values calculated from the empirical equation of Gill. The thermodynamic functions, Gibbs energy (Δ G _A ^o), enthalpy (Δ H _A ^o) and entropy (Δ S _A ^o) for the process of ion-pair formation as well as the activation energy of the ionic movement (ΔH ^∗) have been evaluated. The obtained results are discussed in terms of ion-ion and ion-solvent interactions.     

Modelling spur chemistry for alkaline and acidic water at high temperatures

The effect of pH and associated ionic strength on the primary yields in the radiolysis of pressurised water has been assessed by diffusion-kinetic calculations for temperatures in the range 100–300°C. Account has been taken for ionic strength I up to 0.1 mol kg⁻¹, assuming that the counter ions of H⁺ in acid solutions and of OH⁻ in base solutions have unit charge. In acid solutions, the H⁺ ions react with e⁻ _aq. The decrease in G(e⁻ _aq) and the increase in G(H) with decreasing pH becomes substantial for [H⁺] ≥ 1 × 10⁻⁴ m, but the primary yields of oxidising species are almost constant. In alkaline solutions, the OH⁻ anions affect the spur chemistry of radiation-generated protons and hydroxyl radicals for [OH⁻] ≥ 1 × 10⁻⁴ m. The scavenging of H atoms and hydrogen peroxide becomes significant for [OH⁻] ≥ 1 × 10⁻² m. The total yields G(OH) + G(O⁻) and G(H₂O₂) + G(HO₂ ⁻) are independent of base concentration below 0.01 m. In more alkaline solutions, G(OH) + G(O⁻) increases, whereas G(H₂O₂) + G(HO₂ ⁻) decreases with increasing [OH⁻]. Calculations showed the substantial yield of the reaction O⁻ + e⁻ _aq in 0.1 m base solution. Spur chemistry in alkaline hydrogenated water is not affected by the presence of H₂ if less than 0.001 m of hydrogen is added.     

Synthesis and structures of nickel(II) trimethylacetate dimers with coordinated diamines

Thermal decomposition of the tetranuclear nickel(II) complex Ni₄lη²-o-(NH₂)(NHPh)C₆H₄|₂(MeCN)₂(μ-OOCCMe₃)₄(η²-OOCCMe₃)₂ (I) under an inert atmosphere (o-xylene, 140 °C) was investigated. Under these conditions, the asymmetric binuclear complex Ni|η²-o-(NH₂)(NHPh)C₆H₄‖(η¹-o-(NH₂))(NHPh)C₆H₄|(η²,η-O,O-OOCCMe₃)(η²-OOCCMe₃) (2) was formed at the first stage. Complex2 was converted into the symmetric dimer Ni|η¹-o-(NH₂)(NHPh)C₆H₄|(μ-OOCCMe₃)₄ (3) upon recrystallization from benzene. The structures of complexes2 and3 were established by X-ray diffraction analysis. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1915–1918, November, 2000.     

Vanadium(V) 8-quinolinolate—monomer or dimer?

Extraction of vanadium(V) with 8-quinolinol into chlorobenzene is discussed. Three dimeric species are shown to be responsible for the extraction: 2VO₃^- + 4(HOx)_o α (V₂O₃Ox₄)_o + 2OH^-; log K_ex,1 = -1.60 ± 0.10 2VO₃^- + 4(HOx)_o + H⁺ + ClO₄^- α (V₂O₃H(Ox)₄ · ClO₄)_o + 2OH^-; log K_ex,2 = 1.55 ± 0.10 2VO₃^- + 4(HOx)_o + 2H⁺ + 2ClO₄^- α (V₂O₂Ox₄ · 2ClO₄)_o + 2OH^-; log K_ex,3 = 2.65 ± 0.10 The vanadium(V) complex of 8-quinolinol has also been studied by thermogravimetry and i.r. and visible spectroscopy; an oxo-bridged dimeric structure is postulated. In contrast to 8-quinolinol, 2-methyl-8-quinolinol gives a monomeric vanadium(V) complex under the usual experimental conditions.     

Kinetics and mechanism of the reactions of hexaaqua rhodium (III) with sulphur (IV) in aqueous medium

An O-bonded sulphito complex, Rh(OH₂)₅(OSO₂H)²⁺, is reversibly formed in the stoppedflow time scale when Rh(OH₂) ₆ ³⁺ and SO₂/HSO ₃ ⁻ buffer (1 <pH< 3) are allowed to react. For Rh(OH₂)₅OH₂₊+ SO₂ □ Rh(OH₂)₅(OSO₂H)²⁺ (k₁/k_-1), k₁ = (2.2 ±0.2) × 10³ dm³ mol⁻¹ s⁻¹, k₋1 = 0.58 ±0.16 s⁻¹ (25°C,I = 0.5 mol dm⁻³). The protonated O-sulphito complex is a moderate acid (K _d = 3 × 10⁻⁴ mol dm⁻³, 25°C, I= 0.5 mol dm⁻³). This complex undergoes (O, O) chelation by the bound bisulphite withk= 1.4 × 10⁻³ s⁻¹ (31°C) to Rh(OH₂)₄(O₂SO)⁺ and the chelated sulphito complex takes up another HSO ₃ ⁻ in a fast equilibrium step to yield Rh(OH₂)₃(O₂SO)(OSO₂H) which further undergoes intramolecular ligand isomerisation to the S-bonded sulphito complex: Rh(OH₂)₃(O₂SO)(OSO₂)^- → Rh(OH₂)₃(O₂SO)(SO₃)⁻ (k _iso = 3 × 10⁻⁴ s⁻¹, 31°C). A dinuclear (μ-O, O) sulphite-bridged complex, Na₄[Rh₂(μ-OH)₂(OH)₂(μ-OS(O)O)(O₂SO)(SO₃) (OH₂)]5H₂O with (O, O) chelated and S-bonded sulphites has been isolated and characterized. This complex is sparingly soluble in water and most organic solvents and very stable to acid-catalysed decomposition     

Solvation of ions. Part XXIX. Ionic conductances in acetonitrile-water and pyridine-water mixtures

The limiting conductance of various salts of Na⁺, Ag⁺, Cu⁺, Cu²⁺ and Ph₄As⁺ in acetonitrile-water (AN-H₂O) and pyridine-water (Py–H₂O) mixtures are reported. Single ion values are calculated for AN-H₂O mixtures using the TATB assumption [_o(Ph ₄ As ⁺) = _o(Ph ₄ B ^–)]. The trends observed for the limiting Walden products (_o) of the electrolytes and individual ions are discussed in terms of specific ion-solvent interactions and the structural effects of the solvent mixtures.Deceased, August 30, 1982.     

Composition of the gas phase over Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and the enthalpies of atomization of AlO,Al<Subscript>2</Subscript>O,and Al<Subscript>2</Subscript>O<Subscript>2</Subscript>

The A1, O, AlO, A1₂O, Al₂O₂, WO₂, and WO₃, partial pressures in the vapor over Al₂O₃ in a tungsten Knudsen effusion cell between 2300 and 2600 K were derived from A1⁺, O⁺, AlO⁺, A1₂O⁺, Al₂O₂⁺, WO₂⁺, and WO₃⁺, ion intensities. The mass spectrometer was calibrated against the equilibrium constant of the WO₃(g) = WO₂(g) + O(g) reaction. Refined values of the ionization cross sections of AlO and A1₂O₂ were used in the partial pressure calculations. The enthalpies of atomization of aluminum suboxides were determined to be Δ_at H ^o(AlO, g, 0) = 510.7 ± 3.3 kJ mol⁻¹, Δ_at H ^o(Al₂O, g, 0) = 1067.2 ± 6.9 kJ mol⁻¹, and Δ_at H ^o(Al₂O₂, g, 0) = 1556.7 ± 9.9 kJ mol⁻¹.     

Pulse radiolysis study of 2-Mercapto-benzothiazole-a corrosion inhibitor

Pulse radiolysis of 2-Mercaptobenzothiazole (2-MBT) has been undertaken in aqueous solution. The semi-oxidized species formed at pH 4.5 due to the reaction of OH^•, Br₂ ^•− and N₃ ^• and at pH 10.5 with OH^• yielded a spectrum with λ_max = 348 and 595 nm. These semi-oxidized species were able to oxidize phenothiazine drugs (E^o⋟0.8 V). Reducing species such as e_aq ⁻, CO₂ ^•− and H^• atoms react with 2-MBT resulting in the formation of a transient having λ_max = 350 nm and reducing in nature. Kinetic and spectroscopic data of interest are reported.     

Solvent Effect on Deprotonation Equilibria of Acids of Various Charge Types in Non-aqueous Isodielectric Mixtures of Protic Ethylene Glycol and Dipolar Aprotic N,N-Dimethylformamide at 298.15 K

Deprotonation constants of phthalic (H₂A) and biphthalic (HA⁻) acids and of mono-protonated (BH⁺) and di-protonated (BH₂²⁺) piperazine acids have been determined at 25 °C by measuring the Emf of galvanic cells comprising H⁺-sensitive glass GE(H⁺) and Ag,AgCl electrodes in non-aqueous isodielectric mixtures of protic ethylene glycol (EG) and dipolar aprotic N,N-dimethylformamide (DMF). Solvent effects on deprotonation of the acids: ∂(ΔG _diss^o)=2.303RT[p(_s K _a)−p(_R K _a)], have been dissected into transfer Gibbs energies, ΔG _t^o _, of the species involved by evaluating ΔG _t^o of the uncharged phthalic acid and base piperazine (B) from the measured solubilities of the acid and base, respectively, and using ΔG _t^o of H⁺ based on the TATB reference electrolyte assumptions, as evaluated earlier. The contributions of the different species involved in the protolytic equilibria i.e., H⁺,H₂A,HA⁻,BH₂²⁺ and BH⁺ and their respective conjugate bases HA⁻,A²⁻,BH⁺ and B have been discussed in terms of their solvation behavior as guided by the ‘acid-base’, dispersion, structural and electronic characteristics of the acid-base species and of the co-solvent molecules and binary mixtures, ignoring the Born-type electrostatic interactions on the ionic species as the solvent system is quasi isodielectric.     

The thermodynamic properties of 2-ethylhexyl acrylate over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependence of the heat capacity C _p ^o= f(T) 2 of 2-ethylhexyl acrylate was studied in an adiabatic vacuum calorimeter over the temperature range 6–350 K. Measurement errors were mainly of 0.2%. Glass formation and vitreous state parameters were determined. An isothermic shell calorimeter with a static bomb was used to measure the energy of combustion of 2-ethylhexyl acrylate. The experimental data were used to calculate the standard thermodynamic functions C _p ^o(T), H ^o(T)-H ^o(0), S ^o(T)-S ^o(0), and G ^o(T)-H ^o(0) of the compound in the vitreous and liquid states over the temperature range from T → 0 to 350 K, the standard enthalpies of combustion Δ_c H ^o, and the thermodynamic characteristics of formation Δ_f H ^o, Δ_f S ^o, and Δ_f G ^o at 298.15 K and p = 0.1 MPa.     

Characterizing the Intramolecular H-bond and Secondary Structure in Methylated GlyGlyH<Superscript>+</Superscript> with H<Subscript>2</Subscript> Predissociation Spectroscopy

We report vibrational predissociation spectra of the four protonated dipeptides derived from glycine and sarcosine, GlyGlyH⁺•(H₂)_1,2, GlySarH⁺•(D₂)₂, SarGlyH⁺•(H₂)₂, and SarSarH⁺•(D₂)₂, generated in a cryogenic ion trap. Sharp bands were recovered by monitoring photoevaporation of the weakly bound H₂ (D₂) molecules in a linear action regime throughout the 700–4200 cm^–1 range using a table-top laser system. The spectral patterns were analyzed in the context of the low energy structures obtained from electronic structure calculations. These results indicate that all four species are protonated on the N-terminus, and feature an intramolecular H-bond involving the amino group. The large blue-shift in the H-bonded N–H fundamental upon incorporation of a methyl group at the N-terminus indicates that this modification significantly lowers the strength of the intramolecular H-bond. Methylation at the amide nitrogen, on the other hand, induces a significant rotation (~110^o) about the peptide backbone.     

Kinetics of oxidation of acidic amino acids by sodium N-bromobenzenesulphonamide in acid medium: A mechanistic approach

Kinetics of oxidation of acidic amino acids (glutamic acid (Glu) and aspartic acid (Asp)) by sodium N-bromobenzenesulphonamide (bromamine-B or BAB) has been carried out in aqueous HClO₄ medium at 30°C. The rate shows first-order dependence each on [BAB]_o and [amino acid]_o and inverse first-order on [H⁺]. At [H⁺] > 0·60 mol dm⁻³, the rate levelled off indicating zero-order dependence on [H⁺] and, under these conditions, the rate has fractional order dependence on [amino acid]. Succinic and malonic acids have been identified as the products. Variation of ionic strength and addition of the reaction product benzenesulphonamide or halide ions had no significant effect on the reaction rate. There is positive effect of dielectric constant of the solvent. Proton inventory studies in H₂O-D₂O mixtures showed the involvement of a single exchangeable proton of the OH⁻ ion in the transition state. Kinetic investigations have revealed that the order of reactivity is Asp > Glu. The rate laws proposed and derived in agreement with experimental results are discussed.     

Thermal properties of potassium bis(oxalato)diaquochromates(III) in solid state. Trans–cis isomerization of the [Cr(C2O4)2(OH2)2]? complex ion in aqueous solutions

The thermal decomposition of trans-K[Cr(C₂O₄)₂(OH₂)₂]·3H₂O and cis-K[Cr(C₂O₄)₂(OH₂)₂] has been studied using the TG–MS technique. The measurements were carried out in an argon atmosphere over the temperature range of 293–873 K. The influence of the complex structures and configurational geometry on the stability of the transition products and the pathways of thermal transformations has been discussed. Furthermore, the kinetics of the isomerization reactions of the [Cr(C₂O₄)₂(OH₂)₂]⁻ complex ion catalyzed by five different metal ions: Be²⁺, Mg²⁺, Ca²⁺, Sr²⁺ and Ba²⁺ have been studied. The isomerization reactions were studied in aqueous solution at five various temperatures (283–303 K), at constant concentration of metal ions (C = 0.1 M) and the constant ionic strength of solution (Na⁺, NO₃ ⁻) I = 2.4 M. The rates of the isomerization reaction were determined spectrophotometrically by monitoring of absorbance changes at 410 nm.     

The Arrangement of First- and Second-shell Water Molecules Around Metal Ions: Effects of Charge and Size

Structural features of clusters involving a metal ion (Li⁺, Na⁺, Be²⁺, Mg²⁺, Zn²⁺, Al³⁺, or Ti⁴⁺) surrounded by a total of 18 water molecules arranged in two or more shells have been studied using density functional theory. Effects of the size and charge of each metal ion on the organization of the surrounding water molecules are compared to those found for a Mg[H₂O]₆²⁺• [H₂O]₁₂ cluster that has the lowest known energy on the Mg²⁺• [H₂O]₁₈ potential energy surface (Markham et al. in J Phys Chem B 106:5118–5134, 2002). The corresponding clusters with Zn²⁺ or Al³⁺ have similar structures. In contrast to this, clusters with a monovalent Li⁺ or Na⁺ ion, or with a very small Be²⁺ ion, differ in their hydrogen-bonding patterns and the coordination number can decrease to four. The tetravalent Ti⁴⁺ ionizes one inner-shell water molecule to a hydroxyl group leaving a Ti⁴⁺(H₂O)₅ (OH⁻) core, and an H₃O⁺• • • H₂O moiety dissociates from the second shell of water molecules. These observations highlight the influence of cation size and charge on the local structure of hydrated ions, the high-charge cations causing chemical changes and the low-charge cations being less efficient in maintaining the local order of water molecules. Electronic Supplementary Material: Supplementary material is available for this article at http://dx.doi.org/10.1007/S00214-005-0056-2.     

Electron transfer. 138. Potentials involving chelated chromium(V)

The bis(chelated) complex of Cr^V(0) derived from the dianion (L^{2 −}) of 2-ethyl-2-hydroxybutanoic acid is readily reduced to a bis(chelate of Cr^III, featuring the monoanion (LH⁻) [Cr ^V(0)(L²⁻)₂]⁻+4H⁺+H₂O+2e⁻→[Cr^III(OH₂)₂(LH⁻ ₂]⁺ of this acid. Potentials estimated by Ghosh in 1993 for this 2e⁻ change, E⁰ (pH 0) 1.32 V, E^eff (pH 3.3) 0.93 V, are in accord with the nearly irreversible reductions of the Cr(V) species (in 1∶1 ligand buffer) by Fe²⁺, V0²⁺, IrCl₆ ^{3 −} and I⁻, whereas lower values reported by Bose in 1996, E⁰ (pH 0) 0.84 V, E^eff (pH 3.3) 0.45 V, are potentiometrically inconsistent with these conversions. A similar discrepancy is noted for potentials for Cr(V,IV) estimated in 1996, E⁰ (pH 0) 0.84 V, E^eff (pH 3.3) 0.46 V, which, wholly contrary to observation, predict that the reductions of excess Cr(V) to CR(IV) by Fe²⁺, V0²⁺, and I⁻ are thermodynamically disfavored.     

Intriguing Role of a Quaternary Ammonium Cation in the Dissociation Chemistry of Keggin Polyoxometalate Anions

The gas-phase fragmentations of a series of Keggin polyoxometalate anions with molecular formula of TBA_n[XM₁₂O₄₀] (X = P, Si; M = Mo, W) were studied by electrospray ionization tandem mass spectrometry. The bare polyoxoanions [XM₁₂O₄₀]^n- as well as the non-covalent complexes {TBA[XM₁₂O₄₀]}^(n-1)- and {TBA_m[XM₁₂O₄₀]₂}^3- displayed characteristic dissociation pathways. Fragmentation of [XM₁₂O₄₀]^n- led to pairs of complementary product anions whose total stoichiometry and charge matched those of the precursor anion, consistent with the previous study by Ma et al. The nature of the non-covalent interaction between [XM₁₂O₄₀]^n- and TBA⁺ was addressed in detail via the example of {TBA[XM₁₂O₄₀]}^(n-1)-. The non-covalent interaction [1] primarily dominated by the Coulombic attraction of the opposite charges completely changed the dissociation chemistry of [XM₁₂O₄₀]^n-. The non-covalent complexes {TBA[XM₁₂O₄₀]}^(n-1)- and {TBA_m[XM₁₂O₄₀]₂}^3-, formed by the charge reduction during the electrospray process, underwent distinct dissociation routes: {TBA[XM₁₂O₄₀]}^(n-1)- fragmented to give rise to its product ion {(C₄H₉)[XM₁₂O₄₀]}^(n-1)- by cleaving the N−C covalent bond inside the TBA⁺ cation whereas {TBA_m[XM₁₂O₄₀]₂}^3- dissociated into a pair of product ions, {TBA_i[XM₁₂O₄₀]}^2- and {TBA_m-i[XM₁₂O₄₀]}^-, by breaking the non-covalent bond between [XM₁₂O₄₀]^n- and TBA⁺. In addition, energy-variable CID was used to map the relative stabilities of the ion clusters in the gas phase, which was in excellent agreement with the relative orders of thermal stability in the condensed phase.     

Ionic solvation in water + co-solvent mixtures. Part 8. Total free energies of transfer and free energies of transfer with the “neutral” component removed of single ions from water into water + acetone

The acid dissociation constants of a wide range of acids in water+acetone mixtures have been combined with values for the free energy of transfer of the proton. ΔG⁰_t(H⁺ to calculate values for the free energy of transfer of ions which derive only from the charge on the ion. ΔG⁰_t(i)_c. As the values of ΔG⁰_t(H⁺) have been revised, revised values for the total free energies of transfer of cations and anions, ΔG⁰_t(M⁺) and ΔG^o_t(X^-), are given. New data for ΔG^o_t(MX_n) is also split into values for ΔG⁰_t(Mⁿ⁺) (where n=1 and 2) and ΔG⁰_t(X^?). These free energies of transfer, both total and those deriving from the charge alone, are compared with similar free energies in other mixtures water+co-solvent. Values for ΔG^o_t(i)_c do not conform to a Born-type relationship and show the importance of structural effects in the solvent even when only the transfer of the charge is involved.