Ionenpaargleichgewichte komplexer Carbeniumionensalze als Modelle für die aktive Spezies bei der kationischen Polymerisation

Ion-pair Equilibria of Complex Carbenium Ion Salts as Models of the Active Species in Cationic Polymerization The dissociation equilibria of complex carbenium ion salts [(C₆H₅)₃C^⊕, C₇H₇^⊕MtX^⊖_n+1] have been determined in chloroform, dichloroethane and nitromethane from conductance measurements. The dissociation constants remain almost unchanged for different anions, are however influenced markedly by the polarity of the solvent. The fractions of free and paired ions in these solvents have been calculated. Furthermore the enthalpies and entropies of dissociation have been evaluated.     

Synthesis and anion-sensing property of a family of Ru(II)-based receptors containing functionalized polypyridine as binding site

A family of fluoroionophores have been synthesized incorporating Ru(II)-bipyridine moiety as fluorogenic unit and amino/benzenesulphonamido functionalized 1,10-phenanthroline moiety, attached to Ru(II), as binding sites. Two of the ligands and one of the complexes have been characterized crystallographically. Anion recognition property, studied by luminescence, UV–vis and ¹H NMR spectroscopy, with a large number of anions exhibit strong complexation with F^?, H₂PO₄^? and AcO^?. Binding constants have been determined from luminescence titration and ¹H NMR study gave insight about binding site of anions. Bidentate chelating nature of the H₂PO₄^? and AcO^? anions and steric crowding created by benzenesulphonamide moiety has significantly influenced binding constants and selectivity.     

ENERGY ADDITIVITY IN GLASSES *

Energies of dissociation into the component ions have been computed for many simple and complex oxides. From these, 51 energy constants have been obtained, which may be used to compute approximate ionic dissociation energies in crystals and glasses in which each “metallic” atom is surrounded by oxygens. The relation of these constants to the Periodic Table is shown and briefly discussed. Slight deviations from additivity in silicates and phosphates are related to the dependence of the energy on the number of oxygens in SiO₄and PO₄ groups which are shared with other & or P atoms.     

Cinetique electrochimique du couple cobalt(III)—cobalt(II) en milieu acide phosphorique concentre

The electrochemical behaviour of the cobalt(III)—cobalt(II) couple in 96.5% and 85 wt% H₃PO₄ have been studied at a stationary gold electrode by using chronopotentiometry and triangular voltamperometry. The results have shown that the Co(III)—Co(II) system is reversible and the electrode reaction involves a single electron. The Co(II) ions' diffusion coefficient in the two phosphoric acid solutions was determined as 4.3 × 10⁻⁸ cm².s⁻ in 96.5% wt % H₃PO₄ and 1.2 × 10⁻⁷ cm².s⁻¹ in 85 wt % H₃PO₄. The stabillity of the Co(III) ion in 96.5 wt % H₃PO₄ media was also investigated.     

Potentiometric study on the composition and stability of acetylacetoneanthranilic acid (SCHIFF's base) Complexes of Zinc (II) and Palladium (II)

The condensation of acetylacetone with anthranilic acid in presence of piperidine as the condensing agent gives acetylacetoneanthranilic acid SCHIFF 'S base (H₂AA) which forms complexes with Zinc (II) and Palladium (II). The dissociation constants of H₂AA have been determined by interpolation at half n̄ values and also by algebraic method which give the values 4.85 and 8.25 at 30° ± 1 °C for the dissociation constants. The stability constants of Zinc (II) and Palladium (II) complexes have been determined adopting CALVIN and MELCHIOR 'S extension of BJERRUM 'S method and the values of log k₁ are found to be 2.92 and 3.97 respectively at 30° ± 1 °C. In these complexes 1:1 metal-ligand stoichiometry is observed.     

Spectrophotometric study of dissociation of p-nitroanilinium ion in urea-water solvents at 25°C—effect of solvent

The dissociation constants (K_s) of p-nitroanilinium ion have been determined at 25°C spectrophotometrically in urea-water mixtures containing 11.52, 20.31, 29.64 and 36.83 wt.% urea. Standard free enrgies of transfer, ΔG°_t(B) of the base p-nitroaniline from water to the mixed solvents have been evaluated at 25°C from the measurement of solubilities. Strength of the acid, p-nitroanilinium ion increases with the increase in proportion of urea in the solvents, the rate of increase being sharp at the begining. The solvent effect on the dissociation of the acid: δ(ΔG°) = 2.303 RT [p(K_s) ? p(K_w)] is unusually large in urea—water solvent system compared to those in aqueous mixtures containing methanol, ethylene glycol, acetone and acetic acid. Solvent effect has been discussed in terms of the standard free energies of transfer (ΔG°_t) from water to aqueous urea solvents of the uncharged base (B), the hydrochloride of the base (BHCl) and the hydrochloric acid (HCl) and also of the individual species involved in the dissociation process. The corresponding data in ethylene glycol—water solvent system obtained from literature are also compared. The difference in solvent effects on the dissociation in the two solvent systems has been shown to result from the contrasting behaviour of ΔG°_t(H⁺)?ΔG°_t(BH⁺) arising from the difference in the extent of the solute—solvent interactions.     

Gas transport properties of soluble aromatic polyimides with sulfone diamine moieties

Aromatic polyimides derived from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and 3,3′- or 4,4′-diaminodiphenylsulfone (m-DDS or p-DDS) have been synthesized with a chemical imidization. The disappearance of amic acid groups and the appearance of imide groups are determined by IR and ¹H-NMR spectroscopies. The obtained polyimides are amorphous and soluble in organic solvents. The gas transport properties of the polyimide membranes to CO₂, O₂, N₂, and CH₄ have been determined at 35°C and at a pressure up to 10 atm. The (PCO₂/PCH₄) and (PO₂/PN₂) selectivities of the membranes are augmented due to their large gas diffusivity selectivities. This is considered to be due primarily to the high packing density of polymer chain. © 1995 John Wiley & Sons, Inc.     

Acid dissociation constants of anilinium and mono-nitro anilinium ions in formamide

The acid dissociation constant of anilinium ion and those of o-, m- and p-nitro anilinium ions have been determined accurately in formamide over the temperature range 10–50°C (283.15–323.15 K) from the measurement of the emf of the cells, Pt, H₂/B(m₁), BHCl(m₂)/AgClAg.The dissociation constants at 25°C (298.15 K) have been checked by determining the same with the help of the cells, Pt, Q-QH₂/B(m₁), BHCl(m₂/AgClAg.Thermodynamical changes ΔG⁰, ΔH⁰ and ΔS⁰ for the dissociation processes have been evaluated. The results show that the dissociation constants of these conjugate acids are in general lower (pK_a's higher) in formamide than their corresponding values in water.     

Solvent extraction of hydrofluosilicic acid with alamine 336

Extraction constants for the solvent extraction of hydrofluosilicic acid with Alamine 336 have been determined. Two species were identified, (R₃NH⁺ )₂ SiF₆^2- and R₃NH⁺ HSiF₆, whose respective extraction constants were determined to be log K₂₁ = 7.42 and log K₁₁ = 2.60. For the dissociation of hydrofluosilicic acid the activity coefficient model presented by Bromley was adapted to sulphuric acid and the values used for hydrofluosilicic acid. The effect of the diluent was experimentally investigated.     

SEPARATION OF COBALT(II) AND NICKEL(II) IONS FROM ACID AQUEOUS SOLUTIONS BY Co IT ION-EXCHANGE INTO γ-TITANIUM PHOSPHATE

ABSTRACT

The Co²⁺-2H⁺, Ni²⁺-2H⁺, and Co²⁺-Ni²⁺-2H⁺ ion exchange processes into γ-Ti(H₂PO₄)(PO₄)2H₂O were studied. Exchange isothenns and titration curves were obtained. Monometallic half ion exchange phases were formed by using MC₂+HCl (M=Co,Ni) solutions. Equilibrium constants, free energy, enthalpy, and entropy of the Co²⁺-2H²⁺ ion exchange reaction were determined. In (Co,Ni)Cl₂ solutions, bimetallic a half ion exchange substitution solid solution is detected. Equilibrium constant of the Co²⁺-Ni²⁺ substitution process in the γ-Ti(Co_xNi_0.5?x.HPO₄)(PO₄)nH₂O phase at 85°C was determined. In (Co,Ni)Cl₂+HCl solutions, total separation of Co²⁺ and Ni²⁺ is obtained.     

Synthesis of Heptanoic Acid via the Oxidation of Octene-1 by Hydrogen Peroxide under Conditions of Phase-Transfer Catalysis

Results from studying the oxidation of octene-1 by a hydrogen peroxide solution to heptanoic acid in a two-phase liquid system under phase-transfer catalysis conditions are presented. Methyl(tri-n-octyl) ammonium tetra(oxodiperoxotungsto)phosphate [MeOct ₃ ⁿ N]₃{PO₄[WO(O₂)₂]₄} is used as a catalyst. The conditions of the formation of heptanoic acid with a yield of nearly 90% at temperatures below 100°C and atmospheric pressure in a single stage without organic solvents have been determined. The obtained experimental data provide the possibility to recommend this way for the synthesis of monocarboxylic acids from α-alkenes for the creation of green chemistry processes.     

Determination of Rate Constants for Ozonation of Ofloxacin in Aqueous Solution

The ozonation of the quinolone antibiotic ofloxacin in water has been investigated with focus on kinetic parameters determination. The apparent stoichiometric factor and the second-order rate constants of the reactions of ozone and hydroxyl radical with ofloxacin were determined at 20 °C in the pH range of 4–9. The apparent stoichiometric factor was found to be about 2.5 mol O₃/mol ofloxacin regardless of the pH. The rate constant of the reaction between ozone and ofloxacin was determined by a competitive method (pH = 6–9) and a direct ozonation method (pH = 4). It was found that this rate constant increases with pH due to the dissociation of ofloxacin in water. The direct rate constants of ofloxacin species were determined to be 1.0?×?10², 4.3?×?10⁴ and 3.7?×?10⁷ for cationic, neutral-zwitterion and anionic species, respectively. Accordingly, the attack of ozone to ofloxacin mainly takes place at the tertiary amine group of the piperazine ring, though some reactivity is also due to the quinolone structure and oxazine substituent. The rate constant of the reaction between ofloxacin and hydroxyl radical was obtained from UV/H₂O₂ photodegradation experiments. It was found that this rate constant varies with pH from 3.2?×?10⁹ at pH 4 to 5.1?×?10⁹ at pH 9.     

Polymer Complexes XLIV. Potentiometric and Thermodynamic Studies of Monomeric and Polymeric Complexes Containing 2-Acrylamido-2-methylpropanesulfonic Acid

Proton-monomeric ligand dissociation and metal-monomeric ligand stability constants of 2-acrylamido-2-methyl-1-propanesulfonic acid with several metal ions were determined potentiometrically in water and 0.1 M KCl. In the presence of 2,2-azobisisobutyronitrile as an initiator, the dissociation and stability constants of AMS were determined for the polymeric form (PAMS). The influence of temperature on the dissociation of AMS and the stability constants of their complexes in monomeric and polymeric forms were studied. The vinyl group in the monomeric form decreases the electron density and hence reduces the N–H bond strength (lower pK^H ₂ value). The stability constants of the metal complexes in the polymeric form (better complexing agent) are larger than those of the monomeric form.     

Säurestärke und Komplexbildung von Curcuminoiden

Acidity and Complex Formation of Curcuminoids The stoichiometric acid dissociation constants of curcumin 1a and derivatives as well as the stoichiometric stability constants of the Cu(II)- and Ni(II)-complexes of these substances have been determined by pH-potentiometric titrations in dioxane-water mixture. The influence of different substituents on the pK_a-values and the stability constants is discussed. The complexing properties of the  CO CH₂ CO structural element of the ligands are not significantly changed when the phenyl group is substituted by the styryl group. Solid CuL₂-complexes have been characterized. The coordination of the ester group in the tricarbonyl ligand systems 4 was excluded by i.r. spectroscopy.     

Solvent effect on the dissociation of o-nitroanilinium ion in methanol-propylene glycol media at 25°C

The dissociation constants (K_s) of o-nitroanilinium ion have been determined at 25° in methanol, propylene glycol and mixtures of the two components containing 10, 30, 50, 70 and 90 wt. % propylene glycol by spectrophotometric measurements. Standard free energies of transfer, ΔG°_t(B) of o-nitroaniline from methanol to the other solvents have been evaluated from the measurement of solubilities at 25°C. The solvent effect on the proton transfer process of this acid: ΔG°_t[BH⁺?B]_sys = 2.303RT[p(K_s?p(K_m)] has been discussed in terms of the free energies of transfer ΔG°_t from methanol to other solvents, of the uncharged based B, of the hydrochloride of the base (BHCl) computed from the corresponding values for HCl and also of the individual ions assessed from the previous knowledge of ΔG°_t(Cl^?). The corresponding data for the protonated tris(hydroxymethyl)methyl amine [TrisH⁺] and p-nitroanilinium ion in the same solvent system obtained from the literature are also compared. ΔG°_t[BH⁺?B]_sys values for the dissociation of o-nitroanilinium ion have been found to increase less readily with wt.% propylene glycol compared to p-nitroanilinium ion and are in contrast with the decreasing nature of the corresponding values for the TrisH⁺ ion of different chemical nature. Electrostatic effect being negligible in this solvent system, the overall behaviour of these acids is found to be dictated by specific chemical nature of solute-solvent interactions besides the effect of relative solvent basicities.     

Determination of the Dipole Moment of the Charge-Shift Triplet Exciplex from zinc phthalocyanine tetrasulfomorpholide and p-methoxy-benzenediazonium tetrafluoroborate

Triplet exciplexes are known to have usually relatively low polarities, in contrast to singlet exciplexes. It is shown that triplet quenching rate constants of the title system can be used to determine the exciplex dipole moment if it is (plausibly) assumed that the dissociation rate constants of charge-shift exciplexes only depend on the viscosity but not on the polarity of the solvent. The quenching rate constants k_q of the title system in various acetonitrile/acetone or acetonitrile/ethylacetate mixtures are determined and treated by an adapted McRAE equation developed for UV-VIS absorption spectroscopic data. The dipole moment of p-methoxy-benzenediazonium tetrafluoroborate necessary for the solution of the McRAE equation is estimated by a Hammett correlation of known data which gives by extrapolation μ(p-MeO C₆H₄N₂^⊕BF₄^⊖) = 31.4 × 10⁻³⁰ Cm (9.4 Debye). Using this value and a cavity radius of 3.7 × 10⁻¹⁰m (cp. [1]) μ_ex³(ZnPcTSM…p-MeO–C₆H₄N₂^⊕BF₄^⊖)* = 16.0 × 10⁻³⁰ cm (4.8 Debye) is obtained. According to this value the triplet exciplex studied has a lower polarity than the starting diazonium salt.     

Dissociation et hydratation de nitrates alcalins dans le carbonate de propylene aqueux

Dissociation of lithium, sodium, potassium and tetraethylammonium nitrates and perchlorates in propylene carbonate has been studied by conductometry. Dissociation constants of alkali nitrates are 3·14 × 10^?3 (LiNO₃), 8·35 × 10^?3 (NaNO₃ and 1·92 × 10^?2 (KNO₃) at 25°C. The perchlorates and tetraethylammonium nitrate are strong electrolytes. The solubility products are 4·1 × 10^?4 (LiNO₃), 1·2 × 10^?5 (NaNO₃ and 2·5 × 10^?5 (KNO₃). The conductivity of saturated solutions of nitrates in the aqueous solvent has been determined up to 0·6 M water. Results are used to calculate the equilibrium constants for the reaction I^± + H₂O = I^± H₂O; Li⁺ 6·5, Na⁺ 2·5, K⁺ 0·5 and NO^?₃ 2·4. Dissociation constants, solubility products and hydration constants are compared with values reported for other solvents.     

Solvent effect on the dissociation of m- nitroanilinium ion in water-ethylene glycol media at 25°C

The dissociation constants (^sK)_BH⁺ of m-nitroanilinium ion, have been determined at 25°C in aqueous mixtures of 10, 30, 50, 70 and 90 wt.% of ethylene glycol from spectrophotometric measurements. The solvent effect on the dissociation behaviour of this acid: Δ⁰_t(BH⁺ ?B)_sys = 2.303 RT [p(_sK)^N_BH⁺ ?p(^wK)^N_BH⁺] in these media results in a characteristic minimum with change in the solvent composition. The solvent effect has been discussed in terms of the free energies of transfer (ΔG⁰_t) from water to the aqueous glycol solvents, of the uncharged base (B) evaluated from measured solubilities, of the hydrochloride of the base (BHCl) computed from the corresponding values for HCl, and also of the individual ions assessed from the previous knowledge of ΔG⁰_t(Cl^?). The corresponding data for the protonated Tris (hydroxymethyl) methylamine (Tris H⁺) and p-nitroanilinium ion in the same solvent mixtures obtained from the literature are also compared. Solvent effect on the dissociation of m-nitroanilinium ion has been found to be nearly the same as that for the p-nitroanilinium ion with similar chemical composition but different from that observed in the case of Tris H⁺ of different chemical nature.     

Synthesis of LiFe0.4Mn0.6?xNixPO4/C by co-precipitation method and its electrochemical performances

LiFe_0.4Mn_0.6−x Ni _x PO₄/C(x = 0, 0.05, 0.1, and 0.2) composite cathode materials for lithium ion batteries have been prepared by the co-precipitation method using oxalic acid as a precipitator. The structure and morphology of precursors and products have been investigated. Electrochemical tests demonstrate that LiFe_0.4Mn_0.55Ni_0.05PO₄ can deliver a specific capacity of 142 mAh g⁻¹ at 0.1 C, and retains 133 mAh g⁻¹ after 60 cycles. The rate performance of LiFe_0.4Mn_0.6PO₄ is obviously improved by doping Ni. The capacity of LiFe_0.4Mn_0.55Ni_0.05PO₄ at 2 C is 110 mAh g⁻¹.     

Extraction of some mineral acids by tri-n-octyl phosphine oxide

The distribution equilibria of hydrochloric, nitric, perchloric, sulphuric and phosphoric acids between aqueous solutions and a solution of tri-n-octyl phosphine oxide (TOPO) in organic solvents have been investigated. The organic phases were studied by infrared and nuclear magnetic resonance spectroscopy. As a result, it is found that the extraction of these acids is governed by the formation of HCl·TOPO, HNO₃·TOPO and HClO₄·TOPO, of H₂SO₄·2 TOPO and H₂SO₄·TOPO, and of H₃PO₄·3 TOPO, H₃PO₄·2 TOPO and H₃PO₄·TOPO, respectively.