Löslichkeiten und Aktivitätskoeffizienten von H2S in Elektrolytmischungen

From solubility measurements on hydrogen sulfide in aqueous solutions of the composition [H⁺] = HM, [Na⁺] = (I — H) M = A M, [Cl^?] = I M at 25°C, the molar and molal activity coefficients of H₂S have been calculated. The activity coefficients of H₂S in the electrolyte mixtures have been found to be additive functions of the activity coefficients in the individual electrolyte solutions at the same ionic strength. This result is predicted by the internal pressure theory of salt effects on non-electrolyte activity coefficients, provided that the volume change upon mixing two electrolyte solutions of the same ionic strength is zero.     

Reduction kinetics of glycinate complexes of palladium(II) on a dropping-mercury electrode in acid perchlorate solutions

Polarograms for the reduction of glycinate complexes of palladium(II) (5 × 10^?5 M) are obtained in equilibrium solutions of pH 0.8–3.0 with different protonated-glycine concentrations c _Hgly (supporting electrolyte, 0.5 M NaClO₄). It is established that the irreversible wave of reduction of complexes Pd(gly)₂ corresponds to the diffusion limiting current I _d ⁽²⁾ . A similar wave at pH 1.5 and c _Hgly = 0.005 M, as well as at pH 1.0 and c _Hgly = 0.05–0.5 M is preceded by the diffusion limiting current I _d ⁽¹⁾ . Values of the I _d ⁽²⁾ /I _d ⁽¹⁾ ratio are close to the ratio between equilibrium concentrations of Pd(gly)₂] and [Pdgly⁺], calculated using the step stability constant for Pd(gly)₂. This fact testifies to the reduction of complexes Pdgly⁺ in the vicinity of I _d ⁽¹⁾ and complexes Pd(gly)₂, in the vicinity of I _d ⁽²⁾ . At pH 0.8–1.2 and [H₂gly⁺] = 1 × 10^?4 to 5 × 10^?3 there is observed the diffusion-kinetic limiting current of the first wave I ₁ ⁽¹⁾ , which increases with increasing [H⁺] and decreasing [H₂gly⁺]. The nature of the slow preceding chemical stage that occurs during the reduction of complexes Pdgly⁺ is discussed.     

Synthesis and Structural Characterization of Gallium(I) and Indium(I) Cations Coordinated by Pentamethylethylenediamine

Herein we report on the facile access to a Ga^I and In^I complex salt of pentamethyldiethylenetriamine (PMDTA) with the weakly coordinating counterion [Al(OR^F)₄]^– [R^F = C(CF₃)₃]. Thus, the low temperature reaction of [M(PhF)₂]⁺ (M = Ga, In) solutions in 1,2-F₂C₆H₄ (oDFB) with PMDTA yielded the title compounds M(PMDTA)⁺[Al(OR^F)₄]^– (M = Ga 1 , in 2 ) in non-optimized yields. Both compounds are highly sensitive towards air and moisture, have a rather limited lifetime at room temperature, but were structurally characterized.     

Decomposition of oxalate by hydrogen peroxide in aqueous solution

The decomposition rate of oxalate by hydrogen peroxide has been investigated by a KMnO₄ titration method. The rate equation for decomposition of hydrogen peroxide in the aqueous phase is 1n([H₂O₂]/[H₂O₂]₀)=?k₁·t, where k₁=0.2, for [H⁺]<2M, k₁=0.2+0.34([H⁺]?2), for [H⁺]>2M. As the acidity increases over 2M, an acid catalysis effect appeard. The new rate equation proposed for the decomposition of oxalate by hydrogen peroxide is $$ - \frac{d}{{dt}}X_{[OX]} = k_2 [H_2 O_2 ]_0 (1 - X_{[OX]} )(e^{ - k_1 t} - \frac{{[OX]_0 }}{{[H_2 O_2 ]_0 }}X_{[OX]} )$$ The rate constant for decomposition of oxalate, k₂, increased with nitric acid concentration and the effect of hydrogen ion concentration was expressed as k₂=a[H⁺]ⁿ, where the values fora andn were a=1.54, n=0.3 at [H⁺]<2M, a=0.31, n=2.5 at [H⁺]>2M, respectively.     

Inner-sphere oxidation of iron(II) by tris(malonato)cobaltate(III)

The kinetics of oxidation of Fe²⁺ by [Co(C₃H₂O₄)₃]^3? in acidic solutions at 605 nm showed a simple first-order dependence in each reactant concentration. The second-order rate constant dependence on [H⁺] is in accordance with eqn (i) k₂ = k′₂ + k₃[H⁺] (i) where k′₂ and k₃ have values of 73.4 ± 14.0 M ^?1 s^?1 and 353 ± 41 M^?2 s^?1, respectively, at 1.0 M ionic strength (NaClO₄) and 25°C. At 310 nm the formation and decomposition of an intermediate, believed to be [FeC₃H₂O₄]⁺, was observed. The increase in the rate of oxidation with increasing [H⁺] was interpreted in terms of a “one-ended” dissociation mechanism which facilitates chelation of Fe₂₊ by the carbonyl oxygens of malonate in the transition state.     

The kinetics of the reaction of iodine with hydrazine as studied by pulse radiolysis

Pulse radiolysis was utilized to study the iodine — hydrazine reaction in aqueous solutions of pH3 to 7, at I^– concentrations of 0.02 to 0.34M, and a constant ionic strength of 0.35M. The reaction rate was found to be proportional to [H⁺]^–1 and [I^–]^–1. Experimental results support the assumption that the rate-determining step is the reaction of I₂ with N₂H₄ with a rate constant K1.2×10⁷ M^–1s^–1.     

Nucleophilic attack on bent molybdenum and tungsten metallocene complexes

Reactions of some [M(η⁵-C₅H₅)₂L₂]ⁿ⁺ complexes (M  Mo, W; L = ligand; n = 0, 1, 2) with NaBH₄ and LiAlH₄ are reported. New neutral and cationic hydride derivatives of the type [M(η⁵-C₅H₅)₂HL]^m+ (m = 0, 1) are described, in particular the six halohydride complexes [M(η⁵-C₅H₅)₂HX]. The deuteration studies were carried out, but the results do not lead to definite conclusions about the mechanism.     

A kinetic study of the oxidation of 2-pyridinemethanol, 2-pyridinecarboxaldehyde and 2,6-pyridinedimethanol by chromium(VI) in acidic aqueous media

Oxidation of 2-pyridinemethanol (2-pyol), 2,6-pyridinedimethanol (2,6-pydol) and 2-pyridinecarboxaldehyde (2-pyal) by Cr^VI was studied under pseudo-first-order conditions in the presence of a large excess of reductant and at various H⁺ _aq concentrations; [Cr^VI] = 8 × 10^–4 M, [reductant] = 0.025–0.20 M, [HClO₄] = 1.0 and 2.0 M (I = 1.2 and 2.1 M) or 0.5–2.0 (I = 2.1 M). A parabolic dependence of the pseudo-first-order rate constant (k _obs) versus [H⁺] was observed for all the reductants. A linear dependence of k _obs on [2,6-pydol] and, unusually, higher than first-order dependence on [2-pyol] and [pyal] was established. The apparent activation parameters for reactions studied at constant [H⁺] at I = 1.2 and 2.1 M were determined. The presence of chromium species at the intermediate oxidation states: Cr^V, Cr^IV and Cr^II, was deduced based on e.s.r. measurements and the kinetic effects of Mn^II or O₂ (Ar), respectively. Comparison of the available second-order rate constants for aromatic alcohols and aldehydes demonstrated that chelating abilities of the reductant facilitates the redox process, whereas the electron-withdrawing effect caused by protonating the pyridine nitrogen atom acts in the opposite direction. The unusual low reactivity of 2-pyol was ascribed to intramolecular hydrogen bond formation.     

The mechanism of a redox indicator reaction: The kinetics of oxidation of ferrocyphen by nitrous acid

Summary The oxidation of [Fe(phen)₂(CN)₂] and [Fe(bipy)₂(CN)₂] by nitrous acid in sulphuric acid follows the kinetic equation rate = k[H⁺] [HNO₂] [complex] at low acidities. The mechanism is a diffusion controlled reaction between NO⁺ and the complex. Reaction is too slow for satisfactory use as a redox indicator for nitrite titrations at low acidities (0.1 M) [H⁺]. The variation of rate with acidity in more concentrated sulphuric acid (up to 6 M) is interpreted in terms of protonation of the complex to form [Fe(phen)₂(CNH)₂]²⁺.We thank the British Council for a maintenance award for P.R., and the Universidad Tecnica Federico Santa Maria, Valparaiso, Chile, for study leave.     

Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)₂(H₂O)₂]³⁺ in CF₃SO₃H solution ([Co^III] = (2–6) × 10⁻³ m, [ptz] = 2.5 × 10⁻⁴ m, [H⁺] = 0.02 − 0.05 m, I = 0.1 m (H⁺, K⁺, CF₃SO ₃ ⁻ ), T = 288–308 K) and [Co(edta)]⁻ in aqueous HCl ([Co^III] = (1 − 4) × 10⁻³ m, [ptz] = 1 × 10⁻⁴ m, [H⁺] = 0.1 − 0.5 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 313 − 333 K) were studied under the condition of excess Co^III using u.v.–vis. spectroscopy. The reactions produce a Co^II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k _obs) on [Co^III] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)₂(H₂O)₂]³⁺ ion was found to be independent of [H⁺]. In the case of the [Co(edta)]⁻ ion, the k _obs dependence on [H⁺] was linear and the increasing [H⁺] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH ^≠ = 105 ± 4 kJ mol⁻¹, ΔS ^≠ = 93 ± 11 J K⁻¹mol⁻¹ for [Co(en)₂(H₂O)₂]³⁺; ΔH ^≠ = 67 ± 9 kJ mol⁻¹, ΔS ^≠ = − 54 ± 28 J K⁻¹mol⁻¹ for [Co(edta)]⁻.     

Kinetic Study of the Reduction of Bromate Ion by Tris(1,10-Phenanthroline)Iron(II) and Aquoiron(II) Ions — Implication for the Bromate-Gallic Acid Oscillating Reaction

The kinetics of the bromate oxidation of tris(1,10-phenanthroline)iron(II) (Fe(phen)₃²⁺) and aquoiron(II) (Fe²⁺ (aq)) have been studied in aqueous sulfuric acid solutions at μ = 1.0M and with Fe(II) complexes in great excess. The rate laws for both reactions generally can be described as -d [Fe(II)]/6dt = d[Br^?]/dt = k[Fe(II)] [BrO^?₃] for [H⁺]₀ = 0.428–1.00M. For [BrO^?₃]₀ = 1.00 × 10^?4M. [Fe²⁺]₀ = (0.724–1.45)x 10^?2 M, and [H⁺]₀ = 1.00M, k = 3.34 ± 0.37 M^?1s^?1 at 25°. For [BrO^?₃]₀ = (1.00–1.50) × 10^?4M, [Fe²⁺]₀ = 7.24 × 10^?3M ([phen]₀ = 0.0353M), and [H⁺]₀ = 1.00M, k = (4.40 ± 0.16) × 10^?2 M^?1s^?1 at 25°. Kinetic results suggest that the BrO^?₃-Fe²⁺ reaction proceeds by an inner-sphere mechanism while the BrO^?₃-Fe(phen)₃²⁺ reaction by a dissociative mechanism. The implication of these results for the bromate-gallic acid and other bromate oscillators is also presented.     

Mechanistic studies of the selective reduction of ruthenium(III) containing trinuclear oxo complexes by l-ascorbic acid in aqueous solution

The reduction of the Ru(III) oxo-centred trinuclear acetate cations, [Ru₃(??₃-O)(??₂-CH₃CO₂)₆(H₂O)₃]⁺ and [Ru₂Cr(??₃-O)(??₂-CH₃CO₂)₆(H₂O)₃]⁺, by the biological reductant l-ascorbic acid was studied spectrophotometrically under pseudo first-order conditions over the ranges 3.05????pH????4.83 (acetate buffer), 15?°C??????????30?°C and at I?=?0.5?mol?dm^?3 (NaClO₄). The first electron transfer in the redox process resulted in mixed-valence species [Ru₂M(??₃-O)(??₂-CH₃CO₂)₆(H₂O)₃]⁰, where M?=?Ru or Cr, followed by the slow consecutive reduction of other Ru(III) ions. The kinetics of the formation of the mixed-valence species was studied in detail, and a mechanism in support of these data is proposed. The intricate mechanistic details of the subsequent reactions are unclear as the spectral characteristics of the species involved could not be resolved from those of the first intermediate. The final products, however, were found to be Ru(II) (and Cr(III) for the mixed-metal species) in acetate buffer. The electron-transfer mechanism has been proposed to be inner-sphere, as deduced from Marcus cross-relationship. In an aqueous acetate buffer at I?=?1.0?mol?dm^?3 (NaClO₄), the cyclic voltammograms of the complexes were found to be quasi-reversible and pH dependent and have values of 0.18 and 0.19?V (relative to SHE) at pH?=?3.41 for the [Ru₃(??₃-O)(??₂-CH₃CO₂)₆(H₂O)₃]⁺ and [Ru₂Cr(??₃-O)(??₂-CH₃CO₂)₆(H₂O)₃]⁺ cations, respectively.     

Vanadium(III) Complexes with Picolinic Acid and Dipicolinic Acid in Aqueous Solution

The complex species formed in aqueous solution (25 ^∘C, I = 3.0 mol-dm⁻³ KCl ionic medium) between V³⁺ cation and the ligands: picolinic acid (Hpic, HL) and dipicolinic acid (H₂dipic, H₂L), have been studied potentiometrically and by spectrophotometric measurements. The application of the least-squares computer program LETAGROP to the experimental emf (H) data, taking into account the hydrolytic species of V³⁺ ion, indicates that under the employed experimental conditions, the formation of the complexes [VL]²⁺, [V(OH)L]⁺, [VL₂]⁺, [VL₃], [V₂OL₄] with picolinic acid and the complexes [VL]⁺, [V(OH)L], [V(OH)₂L]⁻, [V(HL)(L)], and [VL₂]⁻ with dipicolinic acid were observed. The stability constants of the complexes formed were determined by potentiometric measurements, and spectrophotometric measurements were done in order to perform a qualitative characterization of the complexes formed in aqueous solution.     

ECE mechanism as a tool for the investigation of unstable metal complexes: Part I. Electrochemical reduction of trans-[CoBr2(N)4]+-type complexes on the mercury electrode

A polarographic investigation of trans-[CoBr₂(N)₄]⁺-type complexe where (N)₄ represents (NH₃)₄, (ethylenediamine)₂ and (propylenediamine)₂, has been carried out in acetate buffer solutions. These complexes gave two polarographic waves; the first wave corresponds to the reduction of Co(III) to Co(II) and the second to the reduction of Co(II) to Co(0). The relation between current and time of the first wave in a positive potential is dependent on the dissolution wave due to bromide ions produced by acid hydrolysis and parallel ECE mechanism. Overall reaction is as follows: at the electrode surface, [Co(III)Br₂(N)₄]⁺+e^-→[Co(II)Br₂(N)₄] [Co(II)Br₂(N)₄]+6H₂O→[Co(II)(H₂O₆]²⁺+2Br^-+(N)₄ 2Br^-+2Hg→Hg₂Br₂+2e and in the solution, [Co(III)Br₂(N)₄]⁺+2H₂O→[Co(III)(H₂O₂(N)₄]³⁺+2Br^-The effects of the acid hydrolysis of a tervalent cobalt complex on the current—potential curve were simulated.     

Substituent effects in the mass spectra of diethyl phenyl phosphates

The mass spectra of diethyl phenyl phosphates show substituent effects with electron-donating groups favouring the molecular ion M⁺˙, and the [M? C₂H₄]⁺˙, [M – 2C₂H₄]⁺˙ and [XPhOH]⁺˙ ions. The [PO₃C₂H₆]⁺ (m/z 109) and [PO₃H₂]⁺ (m/z 81) ions are favoured by electron-withdrawing groups. Results suggest that the formation of the [XPhC₂H₃]⁺˙ ion involves rearrangement of C₂H₃ to the position ortho to the phosphate group. Ortho effects are also observed.     

A kinetic study of the oxidation of 3- and 4-pyridinemethanol,and 3- and 4-pyridinecarboxaldehyde by chromium(VI) in acidic aqueous media

Oxidation of 3-pyridinemethanol (3-pyol), 4-pyridinemethanol (4-pyol), 3-pyridinecarboxaldehyde (3-pyal) and 4-pyridinecarboxaldehyde (4-pyal) by Cr^VI was studied under pseudo-first-order conditions in the presence of a large excess of reductant and at various H_aq ⁺ concentrations; [Cr^VI] = 8 × 10^–4 M, [reductant] = 0.025–0.20 M, [HClO₄] = 1.0 and 2.0 M (I = 1.2 and 2.1 M) or 0.5–2.0 (I = 2.1 M). A linear dependence of the pseudo-first-order rate constant (k _obs) on [reductant] and a parabolic function of k _obs versus [H⁺] lead to the rate law: –d[Cr^VI]/dt = (a + b[H⁺]²)[reductant][Cr^VI], where a and b describe the reaction paths via HCrO₄ ^– and H₃CrO₄ ⁺ species respectively, and are composite values including rate constants and equilibrium constants. The apparent activation parameters were determined from second-order rate constants at 1.0 and 2.0 M HClO₄, at three temperatures within the 293–323 K range. The presence of chromium species with intermediate oxidation states – Cr^V, Cr^IV and Cr^II, was deduced based on e.s.r. measurements and the kinetic effects of Mn^II or O₂ (Ar), respectively. The alcohols were oxidized to the aldehydes, and carboxylic acids and the aldehydes to the carboxylic acids. Chromium(III) was in the form of the [Cr(H₂O)₆]³⁺ complex.     

Kinetics and Mechanism of Chromium(III)-Picolinato and Chromium(III)-Dipicolinato Complexes Aquation in HNO3 Solutions

The acid-catalyzed aquation of [Cr(pic)(H₂O)₄]₂ ²⁺ and [Cr(dpic)(H₂O)₃]⁺(pic = picolinic acid anion, dpic = dipicolinic acid dianion) in nitrate(V) media was studied. The reaction is reversible in the case of the pic-complex and practically irreversible in the case of the dpic-complex. It is assumed that the reactive form of the substrate undergoes fast chelate ring-opening followed by protolytic equilibria, followed by the rate of the Cr—O bond breaking of the monodentate bonded ligand which is the rate-determining step. The kinetics of pic/dpic ligand liberation were followed spectrophotometrically in the 0.4–2.0 M HNO₃ range at I= 2.0 M. The following dependences of the pseudo-first order rate constants on [H⁺] have been established:k _obs=a+b[H⁺](where b and a are apparent rate constants for the forward and the reverse reaction of the pic-complex) and k _obs=b[H⁺]+c[H⁺]²(where b and c are apparent rate constants for the dpic liberation). Fast protolytic pre-equilibria, leading to protonation of the carboxylic oxygen atom on the monodentate bonded ligand, preceeds ligand liberation.     

On the hydrolysis of the titanium(IV) ion in chloride media

Determinations of the [Ti(IV)]/[Ti(III) ratio in solutions of titanium(IV) chloride equilibrated with H₂(g), at 25°C in 3 M (Na)Cl ionic medium, have indicated the predominance of the Ti(OH)₂²⁺ species in the concentration ranges 0.5 ? [H⁺] ? 2 M and 1.5 x 10^?3 ? [Ti(IV)] ? 0.05 M. From the equilibrium data the reduction potential has been evaluated Ti(OH)₂²⁺ + 2 H⁺ + e ? Ti³⁺ + 2H₂O, E_oH = (7.7 ± 0.6) x 10^?3 V. The acidification reactions of Ti(OH)₂²⁺ were also studied in 12 M(Li)Cl medium at 25°C by measuring the redox potential of the Ti(IV)/Ti(III) couple as a function of [H⁺]. The potentiometric data in the acidity range 0.3 ? [H⁺] ? 12 M have been explained by assuming Ti⁴⁺ + e ? Ti³⁺, E_o = 0.202 ± 0.002 V Ti⁴⁺ + H₂O ? TiOH³⁺ + H⁺, log K_a1 = 0.3 ± 0.01 Ti⁴⁺ + 2H₂O ? Ti(OH)₂²⁺ + 2H⁺, log K_a1K_a2 = 1.38 ± 0.05.     

Equilibria in aqueous solution between fe(ii) and n-methyliminodiacetic,n-ethyliminodiacetic and npropyliminodiacetic acids

The complex species formed in aqueous solution between Fe(II) and N-methyliminodiacetic acid (MIDA), N-ethyliminodiacetic acid (EIDA) and N-propyliminodiacetic acid (PIDA) were studied at 25°C and ionic strength 0.1 M in KCl. The experimental potentiometric data were analysed with the least-squares computer program LETAGROP, taking into account hydrolysis of the Fe(II) ion. The ionization constants of MIDA, EIDA and PIDA acids are determined for the corresponding ionic strength and temperature. The following complex species were found (ligands, H₂C): MIDA, [FeHC]⁺, FeC and [FeC₂]_2–; EIDA, FeC and [FeC₂]_2–; PIDA, FeC, [FeC₂]_2– and [Fe(OH)C]_–. The corresponding stability constants were determined.     

Standards for pH measurements and first ionization constants ofo-phthalic acid. Methylcellosolve-water solvent mixtures from −10 to 45°C

From reversible emf measurements of the cell Pt/H₂/KHPh+KCl/AgCl/Ag/Pt, reference value pH-metric standards, pH _RVS , for 0.05 mol-kg^–1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 20, 50, and 80 wt % methylcellosolve (2-methoxyethanol, CH₃O-CH₂CH₂OH)-water solvent mixtures from –10 to +45°C, have been determined in compliance with the criteria endorsed by IUPAC. The corresponding values of the first ionization constant ofo-phthalic acid (H₂Ph, benzene-1,2-dicarboxylic acid), which is a key quantity for the acquisition of pH _RVS standards, have been determined from emf measurements of the reversible cell Pt/H₂/H₂Ph+KHPh+KCl/AgCl/Ag/Pt.