Dioxane-water Solvent Research Articles

Studies on complexes of VO(II), Mn(II), Cu(II), Ni(II), Co(II), Zn(II), Fe(III), and UO2(II) with hydrazone β-diketone ligands

The stepwise stability constants of VO(II), Mn(II), Cu(II), Ni (II), Co(II), Zn(II), Fe(III), and UO2(II) metal ions with 2-(2-acetylphenylhydrazone)-5,5-dimethyl-1,3-cyclohexane dione (2-APHDm), 3-(2-acetylphenylhydrazone)pentane-2,4-dione (2-APHA), 2-(2-acetylphenylhydrazone)-1-phenyl-1,3-butane dione (2-APHB), 2-(2-acetylphenylhydrazone)-1,3-diphenyl-1,3-propane dione (2-APHDB), and 3-(2-acetylphenylhydrazone)-1,1,1-trifluoropentane-2,4-dione (2-APHTA) were determined at 30 °C by pH titrations in 75% (v/v) dioxane–water solvent. In addition, metal complexes of three related β-diketones, 2-APHA, 2-APHB, and 2-APHDB have been synthesized and characterized by elemental analysis, uv–visible, ir spectra, and conductance in DMF and magnetic susceptibility measurements. The structure of the complexes have been proposed. Keywords: transition metal complexes of hydrazone-β-diketone ligands.

Complexation of cryptand-222 and 18-crown-6 with some alkali metal ions in several dioxane-water solvent mixtures

The complexation of cryptand-222 and 18-crown-6 with some alkali metal ions in several dioxane-water solvent mixtures was investigated by a competitive calorimetric titration method. The stabilities of the resulting metal ion complexes in the solvent mixtures are discussed in terms of ligand structural features and preferential solvation properties. The results showed that the macrobicyclic diaza polyether with a three-dimensional cavity has a larger capability than 18-crown-6 to encapsulate ionic species and to screen the interactions between encapsulated cations and solvent molecules. Formation of cryptates was both enthalpy and entropy stabilized, whereas the complexes of 18-crown-6 were only enthalpy stabilized.

Solvolysis rates and activation parameters of phenylchloroformate in water-tetrahydrofuran and water-dioxane mixed solvents

Abstract The rates of hydrolysis of phenylchloroformate were measured over the temperature range 30–55 °C in water-tetrahydrofuran and water-dioxane mixtures of different compositions. The influence of solvent variation on reaction rate was examined in terms of changes in the activation parameters. The activation parameters Δ H ★ and Δ S ★ for the solvolysis reaction showed minima at a water mole fraction of about 0.5 in water-tetrahydrofuran solvent mixtures, whereas these parameters increased continuously with increasing concentration of water in water-dioxane solvent mixtures. The results are discussed in terms of the polarity of the medium and the change in the solvent structure.

Reactivity studies on the hydrolysis of iron(II) complexes of substituted phenanthrolines in dioxane–water solvents

The kinetics of the hydrolysis of tris(4,7-diphenyl-1,10-phenanthroline)iron(II), tris(5-phenyl-1,10-phenanthroline)iron(II), and tris(5-nitro-1,10-phenanthroline)iron(II) has been studied in a wide range of dioxane–water mixtures with different acid catalysts (HCl, H2SO4, or p-MeC6H4SO3H) at different temperatures. The effect of the solvent, the substituent on the ligand, and the nature of the conjugate base on the kinetics and the activation parameters is discussed in terms of the solvation of the species and the transition state.

Formation constants of trivalent lanthanide metal ions and hydrazone β-diketones in 75% dioxane – water solvent

A new series of hydrazone β-diketone organic ligands were prepared: 3-(2-acetylphenylhydrazone)pentane-2,4-dione (2-APHA), 2-(2-acetylphenylhydrazone)-1-phenyl-1,3-butane dione (2-APHB), 2-(2-acetylphenylhydrazone)-1,3-diphenyl-1,3-propane dione (2-APHDB), 3-(2-acetylphenylhydrazone) 1,1,1-trifluoropentane-2,4-dione (2-APHTA) and 2-(2-acetyl-phenylhydrazone)-5,5-dimethyl-1,3-cyclohexane dione (2-APHDm). The step formation constants of their 1:1 and 1:2 rare-earth complexes were determined at 30 °C by pH titration in 75% (v/v) dioxane–water solvent. The ionization constant of ligands were also measured. A curious odd–even stability differential was apparent in the (2-APHDm) ligand with the heavier rare earths Gd–Lu. The differential was apparent in both log K1 and log β values and may be sufficient to cause reversal of the usual ion-exchange elution sequence.

Synthesis, oxygenation and catalytic properties of ruthenium(III) saloph complexes

Synthesis and dioxygen affinities of ruthenium(III)-Schiff base complexes with various appended axial base ligands, [Ru(Saloph)(B)Cl] (where Saloph = bis(salicylaldehyde)- o-phenylenediiminato, B = Cl − 1, imidazole 2, 2-methylimidazole 3 and pyridine 4) are reported. The stoichiometry of dioxygen complexes formed was determined by oxygen uptake measurements. Oxygenation studies of complexes 1– 4 reveal a 1:1 dioxygen complex formation. Complexes 1– 4 were also studied for their catalytic activity by employing cyclohexene as a substrate for oxidation at 35°C using water-dioxane solvent medium. Kinetics of the oxidation reaction catalysed by complexes 1– 4 indicate a first-order dependence with respect to catalyst, substrate and dioxygen concentrations, respectively. The product of oxidation was analysed and identified by GLC as the epoxide. A mechanism is proposed for the conversion of cyclohexene to the epoxide, and a subsequent rate law derived with the help of which were determined the values of the rate and equilibrium constants.

Absolute electrode potentials in dioxane-water solvent mixtures and transfer free energies of individual ions

Standard e.m.f. values at 25 ° C for the cells Pt, H 2(g, 1 atm) ¦HI, solvent ¦AgI, Ag and M, Mx ¦solvent ¦AgX, Ag in nine solvent mixtures of dioxane with water, containing up to 80 wt.% dioxane, are reported. The e.m.f. data were used to determine standard absolute potentials of the hydrogen, the Ag, AgX (X  Cl, Br and I) and the M, M + (M  Li, Na, K, Rb and Cs) electrodes in these solvents by a new method reported recently. The radii of the solvated cations and their solvation extent in such media have been evaluated. The standard Gibbs free energies of transfer of individual ions from water to the respective solvents have also been computed. The results are interpreted and discussed in terms of the solvation characteristics of the solvents. The data obtained in the dioxane-water solvent system are compared with those in various aqueous protic and aprotic solvent systems.

The reactivity of aliphatic amines and morpholines in dioxane–water solvent systems

Using the titration of tertiary aliphatic amines as a model a linear relationship for the log equilibrium constant versus the log dielectric constant over a broad range of dioxane–water mixtures is established. Primary and secondary amines are less responsive to changes in dielectric constant, producing linear data of shallower slope. A study of morpholine and N-alkyl-morpholines produces curves that plateau in high dielectric constant regions and display decreasing slope as water concentrations approach zero. Similar behavior for morpholines is observed in low water mixtures where they form proton transfer complexes with p-nitrophenol. Possible reasons for the behavior are discussed.

ChemInform Abstract: METAL CHELATES OF AZO‐PYRIDAZINE DYES. III. CHELATING TENDENCIES OF PYRUVIC AND HIPPURIC MONOHYDRAZONE‐3‐HYDRAZINO‐4‐BENZYL‐6‐PHENYLPYRIDAZINE

AbstractQuantitative GIeichgewichtsuntersuchungen der wie aufgezeichnet synthetisierten, neuen Azopyrazin‐Liganden (I) und (III) werden detailliert beschrieben.

Metal chelates of azo-pyridazine dyes III chelating tendencies of pyruvic and hippuric monohydrazone-3-hydrazino-4-benzyl-6-phenylpyridazine

The synthesis and quantitative equilibrium studies of two new azo-pyridazine ligands, namely the pyruvic (PHP) and hippuric (HipHP) acid derivatives are described in detail. Their acid-base and metal-ligand equilibrium constants in 75% dioxan-water solvent at 30 °C have been calculated from potentiometric and spectrophotometric data. The probable structures are inferred from electronic and vibrational spectral results. Evidence is presented for the formation of protonated complexes withPHP.

Extended Hildebrand Solubility Approach: Sulfonamides in Binary and Ternary Solvents

The extended Hildebrand solubility approach is used to estimate the solubility of sulfonamides in binary and ternary solvent systems. The solubility of sulfisomidine in the binary solvent, dioxane–water, shows a bell-shaped profile with a solubility maximum well above the ideal solubility of the drug. This is attributed to solvation of the drug with the dioxane–water solvent, and indicates that the solute–solvent interaction energy (W) is larger than the geometric mean (δ1δ2) of regular solution theory. The solubilities of sulfadiazine, sulfisomidine, sulfathiazole, and sulfamethoxazole were determined in mixtures of dimethylacetamide, glycerol, and water, and the solubility profiles were well reproduced by use of the extended Hildebrand solubility approach. Since the solubility parameter (δ1 = 11) of the solvent (dimethylacetamide) was approximately equal to the solubility parameters of the sulfonamides, and because of the powerful solvating power of dimethylacetamide, the solubility profiles did not exhibit peaks as observed for sulfisomidine in dioxane–water. When sulfisomidine was dissolved in a ternary mixture, i.e., butyl acetate (δ1 = 8.5), dimethylacetamide (δ1 ≃ 11), and methanol (δ1 = 14.5), a spike was produced in the solubility profile at the solubility parameter of dimethylacetamide. This sharply peaked profile suggests that the two branches be treated as separate solubility curves, which are then independently well reproduced by the extended Hildebrand solubility approach. None of the four sulfonamides yielded log-linear relationships in the ternary mixtures.

Metal complexes of 2-(2′-carboxymethylthio-phenylazo)-5-nitrotoluene—II. Complex formation equilibria with copper(II) ion in several dioxane—water solvent mixtures

Stability constants of copper(II) complexes formed by 2-(2′-carboxymethyl-thiophenylazo)-5-nitrotoluene in dioxane—water solvent mixtures of several different compositions [50, 60 and 75% dioxane (v/v)] were determined from EMF measurements, at 25°C and 0.1 mol dm −3 NAClO 4 ionic medium. Graphical treatment of experimental data gives for the equilibria nA −+Cu 2+ = Cu A n (2- n)+ ( n = 1 or 2), in a solvent with X% (v/v) dioxane, the following values of log β 1, and log β 2 (given here successively). X = 50:2.41, 6.77; X = 60:3.36, 7.45; X = 75:4.33, 7.64. The relation between solvent composition and the values found for the stability constants is discussed. From EMF measurements made with the copper(II) ion-selective electrode, at constant pH, the nature of the effective donor groups in this potentially terdentate ligand is inferred.

The kinetics and mechanisms of the hydrolyses of 1,3-oxathiolanes and 1,3-dithiolanes promoted by mercury(II) and by thallium(III) ions, including the effects of pH and added anions

The kinetics of the mercury(II) ion-promoted hydrolysis of 2,2-diphenyl-1,3-oxathiolane (2) and of 2-phenyl-1,3-dithiolane (4) and of the thallium(III) ion-promoted hydrolysis of 2-phenyl-1,3-oxathiolane (3) and of (4), have been studied at various pH values and ambient anion concentrations using dioxane–water solvents. In the absence of the metal ion the hydrolyses are relatively slow. The mercury-promoted hydrolysis of (2) involves complex kinetic dependencies upon [Hg2+] and [H3O+] and upon the concentrations of added anions. The results support the tentative mechanism previously proposed for the mercury-promoted hydrolysis of (3) which involves at pH > 3 the slow intramolecular attack of mercury-bound aquo species on the C(2) atom of the rapidly formed 1 Hg2+: 1 O,S-acetal adduct (5). For (2), the extra phenyl group reduces the importance of a route found for (3) at pH < 3 which involves the O-protonation of (5). Also for (2) large values of [Hg2+] can lead to a change from the rate-determining hydrolysis of the Hg2+–O,S-acetal adduct to the rate-determining hydrolysis of the resulting O,O-hemi-acetal. The pattern of pH and anion effects found for the mercury(II) ion-promoted hydrolysis of (4) differ completely from those found for (2) and (3). They suggest a simple mechanism involving only a rate-determining intermolecular attack by water on the 1 Hg2+: 1 S,S-acetal adduct (formation constant, K 4.3 × 103 l mol–1). The neutralisation of one positive charge on this adduct leads to a loss of reactivity of ca. 25%; neutralisation of both leads to a great reduction in hydrolysis rate. The thallium(III) ion-promoted hydrolysis of (4) is mechanistically similar to the mercury reaction; the 1:1-adduct is less easily formed (K 2.9 × 102 l mol–1) but reacts ca. 10-fold faster with water. The kinetic form of the thallium-promoted hydrolysis of (3) is especially simple : zero order in [TI3+] and first-order in [H3O+]. It is argued that this should not be interpreted as implying rate-determining hemiacetal hydrolysis for this system.

Metal chelates of azo-pyridazine dyes-II : Chelating tendencies of diacetyl-, benzil- and benzoylethane-monohydrazone-3-hydrazino-4-benzyl-6-phenylpyridazine

The diacetyl-(DAHP), benzil-(BHP) and benzoylethane-(BEHP) derivatives of 3-hydrazino-4-benzyl-6-phenylpyridazine have been prepared and characterized. Their acid-base properties and their equilibria with transition metal ions in 75% dioxan-water solvent at 30°C have been investigated by pH titrimetry. The role of proton and metal ion solvation by the organic solvent has been discussed in view of the results obtained for the lanthanide-BHP systems in different media. Probable structures of the metal chelates are given based on potentiometric data and spectral results for the solid copper chelates. The possibility of forming MHL species were inferred from electronic absorption measurements at different pH values. The use of BHP as an analytical reagent for the determination of copper spectrophotometrically or as a metallochrom indicator in the complexometric titration of Cu(II) ion is also discussed.

Thermodynamics of the interaction of some bivalent metals ions with N-arylthiovioluric acids

Thermoydnamic protonation constants of N-phenylthiovioluric and [PTVA], N-p-tolylthiovioluric acid [ p-to-TVA], N-o-tolylthiovioluric acid [ o-to-TVA] and N-m-tolylthiovioluric acid [ m-to-TVA] and thermodynamic formation constants of the chelates of Cu 2+, Co 2+, Ni 2+, Zn 2+, Fe 2+ and Mn 2+ with these four closely related N-arylthiovioluric acids have been determined at three different temperatures in 80% v/v water-dioxane solvent. The stabilities of complexes follow the order of basicities of ligands and also the electron affinities of bivalent metal ions as measured by their overall ionisation potential. Other factors affecting complex stability of the metal ions were discussed. The stepwise complexation is found to be predominantly enthalpy driven processes.

Evidence for a solvent-induced change in rate-limiting step in the hydrolysis of benzaldehyde dimethyl acetal

Secondary deuterium isotope effects for the hydrolysis of the dimethyl acetal of benzaldehyde-formyl-d have been determined in mixed water-dioxane solvents varying between pure water and 70% dioxane, 30% water, by volume. Between 0 and 20% dioxane, the isotope effect (k/sup H//k/sup D/) decreases from 1.12 to 1.06. Between 20 and 70% added dioxane, the isotope effects increase regularly from 1.06 to 1.15. The decrease in the apparent isotope effect at low concentrations of dioxane may be an artifact of the biphasic kinetics observed due to hemiacetal buildup in the more aqueous media. The increases in k/sup H//k/sup D/ that are observed between 20 and 70% dioxane are interpreted in terms of a change in rate-limiting step from C-O bond cleavage in water to rate-limiting diffusion apart of the alcohol-oxocarbonium ion encounter pair in high concentrations of dioxane. On the basis of this assumption, ratios of the rate constants for internal return and diffusional separation of the complex are estimated. The steady decrease in rho and rho/sup r/ within the series water and 50 and 70% dioxane also suggests an increase in cationic character in the rate-limiting transition state. Isolated resonance structure-reactivity parameters (rho/sup r//rho/sub eq//sup r/) provide estimates of sp/supmore » 2/ character in rate-limiting transition states that are essentially identical with the estimates obtained from the secondary isotope effect studies.« less

6Li-loaded liquid scintillators with pulse shape discrimination

Excellent pulse height and pulse shape discrimination performance has been obtained for liquid scintillators containing as much as 10 wt.% (6)Li-salicylate dissolved in a toluene-methanol solvent system using naphthalene and 9,10 diphenylanthracene as intermediate and secondary solutes. This solution has improved performance at higher (6)Li-loading than solutions in dioxane-water solvent systems, and remains stable at temperatures as low as -10 degrees C. Cells as large as 5 cm in diameter and 15.2 deep have been prepared which have a higher light output for slow neutron detection than (10)B-loaded liquids. Neutron efficiency calculations are also presented.

Anion Exchange Selectivity in Water–Dioxane Medium

Abstract A systematic study of the exchange behavior of the simple monovalent anions ClO4 −, I−, CNS−, and Cl− as a function of the water–dioxane solvent compositions 0, 20, 45, 70, and 82% w/w at 303 ± 0.1°K on strong base anion exchangers such as Dowex 1−X1, Dowex 1−X2, and Dowex 1−X4 as well as on two weak base anion exchange resins (Dowex-3 and Amberlyst A-21) was carried out. The results are analyzed in terms of models proposed by Diamond and Reichenberg. The results agree qualitatively with the above models but fail to provide quantitative agreement.

Polarographic behavior of copper ion in solution of o-carboxyphenylazo-acetylacetone

Copper acetate at pH 6.0 in dioxane-water solvent 25% gives with o-carboxyphenylazo-acetylacetone only one complex of composition 1:1. This complex is reduced at the dropping mercury electrode in solutions of 0.1 M sodium sulphate giving a single irreversible diffusion controlled wave corresponding to two-electron reduction. The half-wave potential of this wave is pH dependent, both in non-buffered and in acetate buffer solutions, and shifts to more negative values by increasing the pH of the solution. The relation between copper concentration and the height of the wave of the complex is linear. An amperometric titration method was given for determining the concentration of copper ion in solution.

Study of the Hammett equation for the ionisation of substituted benzoic acids and phenols in dioxan–water mixtures

The thermodynamic pK values of 17 substituted benzoic acids and 21 substituted phenols were determined in 20, 40, 60, and 80% v/v dioxan–water at 30 ± 0.1 °C and µ0.1M(NaClO4) by the Calvin–Bjerrum potentiometric titration technique. The ‘practical’ pK values of substituted benzoic acids were also determined in 85 and 90% v/v dioxan–water mixtures. The Hammett substituent constants were calculated and the data for the meta- and para-derivatives were utilized to give Hammett reaction constants. It was observed that dρ/dD(D= dielectric constant) was not regular. In the case of the benzoic acids, the ρ values decrease above 0.44 mole fraction dioxan. The ρ values are, however, insensitive to the medium for ortho-substituted compounds. Attempts have been made to explain these observations by considering the structure of the dioxan–water solvent.