Mixed Solvent Media Research Articles

Effect of solvent on the reactions of coordination complexes. Part 9.—Kinetics of solvolysis of cis-(chloro)(cyclohexylamine) bis(ethylenediamine)cobalt(III) in methanol–water, propan-2-ol–water, ethylene glycol–water and t-butyl alcohol–water media

The kinetics of the solvolytic aquation of cis-(chloro)(cyclohexylamine)-bis(ethylenediamine)cobalt(III) ion were investigated in water–methanol, water–propan-2-ol, water–ethylene-glycol (0–80 wt % alcohol) and water-t-butyl alcohol (0–50 wt % alcohol) media at 35–60 °C. Plots of log ksobsvs. D–1s(where Ds is the bulk dielectric constant of the solvent mixture), log ksobsvs. the Grunwald–Winstein solvent parameter, YButCl, and log ksobsvs. Xorg(= mole fraction of cosolvent) tended to be curved. Under isodielectric conditions (Ds≈ 50) at 50 °C, the plot of log ksobsvs. Xorg for methanol–water, ethanol–water, propan-2-ol–water, t-butyl alcohol–water, acetone–water, ethylene glycol–water also did not yield a satisfactory straight line. The observed dependence of solvolysis rate on Xorg has been interpreted in terms of preferential solvation of the initial and transition states which is believed to be at least partly controlled by the overall acidity and basicity of the mixed solvent media as well as the hydrophobic interaction effect. Variation of enthalpies and entropies of activation with solvent composition was correlated with changes in the physical properties of the solvent mixtures. The solvent isotope effect (kH2O/kD2O= 1.38 ± 0.16 at 50 °C) was, however, normal as observed for several other cis-[Co(en)2(primary amine)Cl]2+ complex ions.

Potentiometric titrations in methanol/water medium: Intertitration variability

Homogeneous sets of data from strong acid-strong base potentiometric titrations in a mixed solvent medium (9:1 v/v methanol/water), performed by means of the glass electrode, at various constant ionic strengths and with different reference electrodes, have been analysed by statistical criteria. A standardized procedure has been established to obtain reliable potentiometric data in mixed solvents. It has been demonstrated how, with the aid of a proper linearized model, analysis of variance (ANOVA) applied to the standardization titrations can be used to test the reliability of a potentiometric chain in a medium other than pure water. The error expected in the stability constants thus evaluated is related to the intertitration error of the operational p K* ′ w, for the same medium and the same chain. The results obtained by applying ANOVA to the mixed solvent data substantially confirm the trend found for aqueous media, the intertitration error being larger than the intratitration error for all the parameters investigated ( E ′ 0, p K* ′ w, mean equivalence volume). The stochastic error thus obtained depends on the ionic medium used and on the kind of reference electrode employed in the electrochemical chain.

Studies on ion sorption property and stability of YBa2Cu3O7−x in aqueous and mixed solvent media

Abstract Ion sorption behaviour and stability of YBa 2 Cu 3 O 7−x in water and methanol-water mixture was studied by chemical analyses of the solutions and oxide and X-ray analyses of the oxide after treatment. Ba is preferentially leached from YBa 2 Cu 3 O 7−x by water,whereas in methanol-water mixture leaching of Ba is considerably reduced. The 1-2-3 phase of YBaCuO could not be stabilised by increasing the concentration of methanol in methanol-water mixture. In presence of dissolved NaCl and CaCl 2 in 20 v% methanol-water mixture, the leaching of Ba was further reduced and the residual solid contained mainly the 1-2-3 phase of YBaCuO. It was possible to incorporate Ca into the YBa 2 Cu 3 O 7−x matrix using CaCl 2 dissolved in 20 v% methanol-water mixture. The consequences of treating YBa 2 Cu 3 O 7−x with solutions of salts dissolved in methanol-water mixture on its superconducting property are discussed.

Complexes of divalent ions in mixed solvent media. III. Outer-sphere interactions in amine + diluent solutions

The standard enthalpies and (in part) free energies and entropies of transfer from amine (L) to amine + diluent (D) mixtures have been determined for MX2L2 complexes at 25°C using chloroform, 1,1,2,2,-tetrachloroethane (TCE), benzene, chlorobenzene, and ethyl acetate as diluents (M=Co and Zn; X=Cl and Br; L = pyridine, α-picoline, and γ-picoline). Thermodynamic functions of transfer indicate specific outer-sphere interactions of the complexes with amine and protic diluents (chloroform and TCE) and reveal solvent-solvent interactions of amine + protic diluent mixtures. The effects of the nature of X, L, and M of the MX2L2 complexes on their interaction with the components of the mixed solvent are discussed.

Complexes of divalent inons in mixed solvent media. II. Outer-sphere interactions in pyridine + diluent solutions

The enthalpies and (in part) free energies and entropies of transfer from pyridine to pyridine + diluent mixtures have been determined for MnCl2py4, Mn(NCS)2py4, Co(NCS)2py4, Ni(NCS)2py4, and NiBr2py4 complexes at 25°C using chloroform or 1,1,2,2-tetrachloroethane (TCE) as diluents. The ΔHtro data indicate specific outer-sphere interactions of the complexes with the diluents. The influence of the kind of anionic ligands and central metal ion of the complexes on their interaction with the diluents are discussed.

Water insoluble polyacrylamide part VI: Dilute solution properties of poly(N‐acryloyl‐m‐aminobenzoic acid)

AbstractA high molecular weight poly(N‐acryloyl‐m‐aminobenzoic acid) (PMAB) was synthesized in a mixed solvent medium by radical polymerization. The polymer was separated into different fractions by fractional precipitation. All those eight fractions were characterized by viscometry, vapor pressure osmometry and gel permeation chromatography. Mark‐Houwink‐Kuhn‐Sakurada relationships were established for three different solvents at 30°C. Unperturbed dimensions were estimated from the viscosity‐molecular weight data using graphical methods based on approximate theories of Stockmayer and Fixman, and of Kurata, Stockmayer, and Roig, and on a first‐order perturbation treatment of the excluded volume effect. The results indicate that the PMAB chain is of intermediate stiffness.

Effect of solvent on the reactions of coordination complexes. Part 2.—Kinetics of solvolysis of cis-(chloro)(imidazole)bis(ethylenediamine)-cobalt(III) and cis-(chloro)(benzimidazole)bis(ethylenediamine)cobalt(III) in methanol–water and ethylene glycol–water media

The kinetics of solvolysis of cis-(chloro)(imidazole)bis(ethylenediamine)-cobalt(III) and cis-(chloro)(benzimidazole)bis(ethylenediamine)cobalt(III) have been investigated in aqueous methanol (MeOH) and aqueous ethylene glycol (EG) media (0–80% by weight of MeOH or EG) at 45–64.7 °C. The logarithm of the pseudo-first-order rate constants for MeOH–water media exhibits linear dependence with the reciprocal of the bulk dielectric constant (D–1s), the mole fraction of MeOH (XMeOH) and the solvent ionizing power Y(Y1-AdCl) as determined by the solvolysis rates of 1-adamantyl chloride. Similar plots (log ksobsvs.xEG or D–1s) for EG–water media are non-linear. It is evident that the solvation phenomenon plays dominant role and the rate of solvolysis is mediated by the dual solvent vectors, the overall acidity and basicity of the solvent mixtures. The relative transfer free-energy calculations indicate that the mixed solvent media exert more destabilizing effect on the transition state as compared to the initial state. The activation enthalpy and entropy vs.Xorg(where Xorg is the mole fraction of the organic solvent component) plots display maxima and minima indicating that the solvent structural changes play significant role in the activation process. The activation free energy at a given temperature, however, increases only marginally and linearly with increasing Xorg. The mutual compensatory effect of activation enthalpy and entropy on the activation free energy is in keeping with the fact that the perturbations of the reaction zone and the solvent network remain approximately proportional to each other with increasing Xorg so that the isodelphic and the lyodelphic components of ΔH± and ΔS± correlate well with each other.

Phase Transition of a Polymer Gel in Pure and Mixed Solvent Media

A volume phase transition of poly-N-isopropylacrylamide (NIPA) gel immersed in some pure and mixed solvents has been investigated experimentally. A slightly discontinuous transition of NIPA get in water changed to a more distinctly first-order transition on adding a small amount (<20%) of alcohols to water. As the concentration of alcohols in the mixed solvent increased further, the volume transition blurred and eventually disappeared. Analyzing the experimental results on the basis of the mean field theory of polymer solution, it has been shown that the polymer-solvent interaction parameter χ exhibits a drastic change at the volume transitions. This indicates that the enthalpy and entropy of solution depend strongly on polymer concentration.

Water insoluble polyacrylamide—V. Dilute solution properties of poly( N-acryloyl- o-aminobenzoic acid)

A high molecular weight poly( N-acryloyl- o-aminobenzoic acid) has been synthesized by radical polymerization in a mixed solvent medium. The polymer has been fractionated by fractional precipitation and the fractions characterized by viscometry, vapour pressure osmometry and gel permeation chromatography. Mark-Houwink-Kuhn-Sakurada relationships are developed for three solvents. The values of unperturbed dimensions, (〈 R 0 2〉/ M) 0.5, are evaluated by application of two-parameter theories of the excluded volume effect, developed by Fixman, Kurata, Stockmayer and Roig and by Bueche and James and first order perturbation theory. Based on the value of the conformational parameter σ, the polymer is found to behave as a semiflexible polymer in solution as a result of the increased bulk of the lateral group.

Solute-solvent interaction involving MX2Ln type complexes in mixed solvent media. I. Outer-sphere interactions of the NiCl2py4 complex in pyridine + diluent solutions

The standard enthalpies and entropies of transfer from pyridine to pyridine+diluent mixtures of varying composition have been determined for the NiCl2py4 complex at 25°C using chloroform, 1,1,2,2-tetrachloroethane, aniline, benzene, and chlorobenzene as the diluents. Large negative enthalpies of transfer to solvent mixtures involving the protic diluents contrast with the small effects observed for the aprotic diluents. For the latter, the negative entropies of transfer agree with the assumption that pyridine molecules remain attached to the complex when the diluent is added to pyridine, indicating outer-sphere interaction of the amine with the complex. Solvent effects observed in the near infrared ligand-field spectrum of NiCl2py4 support the assumption of specific outer-sphere interactions with protic diluents. Additional information about these interactions is provided by the CTCT(t2g→π*) metal-to-ligand band in the UV.

Cation exchange in mixed solvent media. 2. Alkali ion and solvent self-diffusion in Dowex 50W-dimethyl sulfoxide-water

Cation exchange in mixed solvent media. 2. Alkali ion and solvent self-diffusion in Dowex 50W-dimethyl sulfoxide-water

Influence of the solvent medium on formation of Cu(II), Zn(II) and Ni(II) hexacyanocobaltates

Investigations on precipitation of metal hexacyanocobaltates from mixed solvent media have confirmed the earlier interpretation of the mechanism and provided further insight into it.

Thermodynamics of the silver—silver chromate electrode in water + 10, + 20, + 30 and + 40 mass percent of dioxane at different temperatures

The emf of the cell: Ag, AgCl, NaCl(m)⋮Na2CrO4(m/2), Ag2CrO4, Ag in water + 10, + 20, + 30, and + 40 mass percent of dioxane has been measured at 5°C intervals over the temperature range 15–45°C. The values of the standard potentials of the silver—silver chromate electrode have been determined in these mixed solvent media at these temperatures. The standard thermodynamic quantities (ΔG°, ΔH°, and ΔS°) for the cell reaction in water + dioxane mixtures have been evaluated at these temperatures. The results are discussed in terms of the preferential solvation of the ions.

A nuclear magnetic resonance investigation of the solvation of nitroaromatic radical anions

Association of water with the radical anions produced by electrolytic reduction of nitrobenzene, 1,4-dinitrobenzene, and pentamethylnitrobenzene has been studied by high-resolution nuclear magnetic resonance spectroscopy. The water resonance of a mixed-solvent medium which consisted of acetonitrile and water in a mole ratio of ca. 19: 1 was examined at 60, 90, and 270 MHz. A linear increase in linewidth of the water signal with increasing frequency required postulation of more than a single water resonance. The water resonance envelope is best reproduced by a sum of three Lorentzian components in each case. For all three radicals it was possible to estimate a hyperfine coupling constant and an exchange lifetime from each resolved component. Data for the nitrobenzene and pentamethylnitrobenzene anions were obtained over a range of water concentrations sufficient that equilibrium constants for association could be calculated; however, this was not possible for the 1,4-dinitrobenzene anion. For nitrobenzene and 1,4-dinitrobenzene anions, the exchange lifetime was about a factor of 10 longer than the rotational correlation time reported for water, 2.7 × 10 −12 sec, while for the pentamethylnitrobenzene anion the exchange lifetime was approximately equal to this correlation time.

Anion exchange in mixed solvent systems

The diffusion of chlorocomplexes of some corrosion and fission products in anion exchange beads has been studied in mixed solvent media. The effects of variables on the kinetics of the exchange process by the batch and flow technique were examined. The strongly basic anion exchanger Dowex 2X8 in its Cl− form was used in organic solvent—water—hydrochloric acid solutions. The dependence of the exchange rate on temperature, the viscosity of the solution, the mean resin particle diameter and the composition of the solution was studied. Film and particle diffusion coefficients were calculated from the experimental data. The results provide valuable data for the design of separation procedures.

Some aspects of ion-exchange in non-aqueous and mixed solvents

The author's published work has been used to illustrate certain aspects of ion-exchange resin stability and sorption behaviour in non-aqueous and mixed solvent media. Solvent and thermal stability have confirmed that even strong-base ion-exchange resins are sufficiently stable in methanol and heptne media at ambient temperature to permit their use in analytical separations. The enhanced selectivity differences of ion-exchange resins for inorganic ions in mixed media is illustrated by the sorption of alkali metal ions on Zeo-Karb 225 (hydrogen form) from aqueous methanol, aqueous ethanol, and aqueous acetone. Finally, on the organic side, the discussion of work on the separation principles of phenols from methanolic media with De-Acidite FF (acetate form) is extended to the wider context of ion-exchange fractionation of peat and petroleum constituents.

ChemInform Abstract: CIRCULAR DICHROISM STUDIES ON THE INTERACTIONS BETWEEN TRIS(L‐ALANINATO)COBALT(III) COMPLEXES AND BASIC POLYELECTROLYTES IN SOLUTION

The circular dichroism spectra of the poly-L-lysine complexes with abc(–), abd(–), and abd(+)Co(L-ala-O)3 in water and isopropyl alcohol–water (1 : 1), at different pH values and over a range of complex to polymer molar ratios, have been measured. Evidence of a specific site binding is presented for abc(–)Co(L-ala-O)3 in the mixed solvent medium. Of the diastereoisomers used, only in the presence of this material does the macroion assume an α-helical conformation at pH values where the coil form normally predominates. The greater the complex to polymer ratio, the greater the proportion of material of α-helical conformation there is present. Directional modes in the binding, very likely involving hydrogen bonding interactions, are indicated by the changes in the visible c.d. spectra of abc(–)-Co(L-ala-O)3 in PLL-50% isopropyl alcohol solutions. In contrast, the same complex destabilizes the α-helix structure of poly-L-ornithine. All these features are examined in the light of the structural characteristics of the interacting species. The influence of solvent composition is also considered. Implications of the different stereochemical features of abd-diastereoisomers on the association process with the polypeptides are discussed.

Cation exchange in mixed solvent media. I. Equilibrium swelling of polystyrenesulfonate resins in dimethyl sulfoxide-water media

Cation exchange in mixed solvent media. I. Equilibrium swelling of polystyrenesulfonate resins in dimethyl sulfoxide-water media

Circular dichroism studies on the interactions between tris (L-alaninato)cobalt(III) complexes and basic polyelectrolytes in solution

The circular dichroism spectra of the poly-L-lysine complexes with abc(–), abd(–), and abd(+)Co(L-ala-O)3 in water and isopropyl alcohol–water (1 : 1), at different pH values and over a range of complex to polymer molar ratios, have been measured. Evidence of a specific site binding is presented for abc(–)Co(L-ala-O)3 in the mixed solvent medium. Of the diastereoisomers used, only in the presence of this material does the macroion assume an α-helical conformation at pH values where the coil form normally predominates. The greater the complex to polymer ratio, the greater the proportion of material of α-helical conformation there is present. Directional modes in the binding, very likely involving hydrogen bonding interactions, are indicated by the changes in the visible c.d. spectra of abc(–)-Co(L-ala-O)3 in PLL-50% isopropyl alcohol solutions. In contrast, the same complex destabilizes the α-helix structure of poly-L-ornithine. All these features are examined in the light of the structural characteristics of the interacting species. The influence of solvent composition is also considered. Implications of the different stereochemical features of abd-diastereoisomers on the association process with the polypeptides are discussed.

Polarographic Studies of Ni(II) Complex with Tyrosine in aqueous and aqueous‐alcoholic media

AbstractThe complexation behaviour of various metal ions with tyrosine and threonine has been recently investigated in our laboratories [1–2]. However, there is hardly any reference regarding polarographic studies on complex forming ability of tyrosine and hence the present studies were undertaken. This communication deals with detailed investigations on the polarographic behaviour of Ni(II)‐tyrosine system in aqueous and mixed solvent media.