Mole Fraction Of DMSO Research Articles

Kinetics of the solvolysis of the trans-dichlorotetrapyridinecobalt(III) ion in water + dimethyl sulphoxide mixtures

The kinetics of the solvolysis of 1,6-[Copy4Cl2]+ have been followed over a range of temperatures in mixtures of water with DMSO up to a mole fraction of DMSO(x2)≈ 0.2. The logarithm of the first-order rate constant varies approximately linearly with the reciprocal of the dielectric constant at the same temperature, contrary to findings for the solvolysis of this complex in mixtures of water with alcohols. Extrema in the enthalpy, ΔH*, and entropy, ΔS*, of activation for solvolysis of the complex in the latter mixtures occur at low x2 of the cosolvent and correlate well with the extrema found in the relative partial molar volume, V2–V°2, of the cosolvent. With additions of DMSO to water, sharp changes in V2–V°2 do not occur until x2≈ 0.2, and extrema for ΔH* and ΔS* also do not occur until x2≈ 0.2 is reached. The application of a free-energy cycle by combining free energies of activation, ΔG*, with free energies of transfer, ΔG°2, shows that the effect of solvent structure is greater on the pentacoordinated cation in the transition state than on the hexacoordinated cation in the initial state.

Calorimetric study of the ionization process for 2,3-dihydroxybenzoic acid

A calorimetric study of the ionization process of 2,3-dihydroxybenzoic acid was performed in water—DMSO mixtures ranging from pure water up to a 0.8 mole fraction of DMSO. A comparison of the ionization processes of the 2,6-dihydroxybenzoic acid with the 2- and 3-monohydroxy substituted benzoic acids was also presented.

The effect of the medium on the dissociation of the para-carboxy aniline ion

A calorimetric study of the dissociation of the p-carboxy aniline ion in water—DMSO mixtures, ranging from pure water up to 0.8 DMSO mole fraction, is presented. This compound is found to be a weaker base than the m-carboxy aniline in all solutions containing DMSO. Different behaviour has been observed in pure water, where the unstable zwitterion form greatly influences the aniline strength.

Calorimetric study of the ionization process for 2,6-dihydroxybenzoic acid. The effect of the internal hydrogen bond on acid strength

The ionization and solution enthalpies of 2,6-dihydroxybenzoic acid were measured calorimetrically at 25°C in water—DMSO mixtures, ranging from pure water up to 0.8 mole fraction of DMSO. The trend of the ionization as a function of the DMSO mole fraction is very different from those of all the monosubstituted-benzoic acids previously studied. This is due to the two internal hydrogen bonds formed between the carboxyl group and the hydroxyl groups.

The effect of the medium on the dissociation of the ortho-carboxy aniline ion. Primary steric effect as a factor in the ionization process

A calorimetric study of the dissociation of the ortho-carboxy aniline ion in water—DMSO mixtures, ranging from pure water up to 0.8 DMSO mole fraction is presented. The primary steric effect is the key factor in the ionization process of the anilinium ion and seems to oppose the formation of the zwitterion in pure water.

The effect of medium on the dissociation of the meta-carboxy aniline ion. A tautomeric effect

A thermodynamic study of the dissociation of the m-carboxy aniline ion in water-DMSO mixtures, ranging from pure water up to 0.8 DMSO mole fraction is presented. A tautomeric zwitterion equilibrium seems to influence the ionization trend in water-rich solutions.

Calorimetric study of the ionization process for 2,4-dinitrophenol in water—dimethylsulphoxide mixtures at 25°C

The ionization and solution enthalpies of 2,4-dinitrophenol were measured calorimetrically at 25°C in water—DMSO mixtures ranging from 0.1 to 0.8 mole fraction of DMSO. The greater acidity of 2,4-dinitrophenol with respect to 2,5-dinitrophenol is explained on the basis of the observation that in the anion the π-withdrawing resonance effect of the para nitro group stabilizes the benzene ring while in the undissociated molecule the contrary is true.

Calorimetric study of the ionization process for 2,5-dinitrophenol in water—dimethylsulfoxide mixtures at 25°C

The ionization and solution enthalpies of 2,5-dinitrophenol were measured calorimetrically at 25°C in water—DMSO mixtures ranging from 0.1 to 0.8 mole fraction of DMSO. The effect of the nitro group in the ortho position seems to prevail over that of the nitro group in the meta position. The greater acidity of dinitrophenol with respect to the mononitro isomers is explained on the basis of the interference of the nitro group in the metaposition on the interactions between the nitro group in the ortho position and the hydroxyl group or phenolate oxygen.

Medium effect on the dissociation of the meta-hydroxyaniline ion

A calorimetric study of the dissociation of the m-hydroxyaniline ion in water—DMSO mixtures, ranging from pure water up to 0.8 DMSO mole fraction, is presented. The solution and neutralization heats of m-hydroxyaniline have also been obtained. On the basis of these measurements, an electrophilic attack of the proton on the benzene ring could be hypothesized.

The effect of medium on the dissociation of the p-hydroxyaniline ion

A thermodynamic study of the dissociation of the p-hydroxyaniline ion in water-DMSO mixtures, ranging from pure water up to 0.8 DMSO mole fraction, is presented.The heats of neutralization of p-hydroxyaniline and its heats of solution have been obtained by calorimetric measurements.The entropy term can be identified as the driving force of the dissociation process.

Thermodynamics of the ionization process for 3,5-dinitrobenzoic acid. The additive effect of a meta substituent on the acid strength

The ionization and solution enthalpies of 3,5-dinitrobenzoic acid were measured calorimetrically at 25°C in water-DMSO mixtures ranging from 0.1 up to 0.8 mole fraction of DMSO. The Δ G 0 values for the ionization process have been determined for these solutions by potentiometric measurements. An attempt has also been made to compare the observed substituent constants to those predicted on the assumption of the additivity principle.

Thermodynamics of the ionization process of phenol in water—dimethylsulfoxide mixtures at 25°C

The ionization and solution enthalpies of phenol were measured calorimetrically at 25°C in water—DMSO mixtures ranging from pure water to 0.8 mole fraction of DMSO. The Δ G 0 values for the ionization process were calculated in the same solutions. The weak acidity of phenol is explained on the basis of the poor resonance effect of the phenate anion in water—DMSO solutions.

Study of the effect of the medium on the entropic and enthalpic reaction constants for the dissociation of nitro-phenols in water—dimethylsulfoxide mixtures at 25°C

The effect of the medium on the reaction constants of the dissociation of nitro-phenols in water-dimethylsulfoxide mixtures ranging from 0.0 to 0.8 mole fraction of DMSO was further investigated. Some more correct reaction constants together with the entropic (ϱ S) and enthalpic (ϱ H) reaction constants give a more complete picture of the effect of the medium.

Density and viscosity of the system Ca(NO3)2-H2O-dimethyl sulphoxide

The density and viscosity of the ternary system Ca(NO3)2-H2O-dimethyl sulphoxide were measured over the temperature range 0 < t < 60 °C, with the mole fraction of the salt in the system varied in the range 0.05 < x < 0.16. The temperature and concentration dependences of density and viscosity have been described by empirical equations. The viscosity data show a pronounced dependence on the solvent composition. Maximum deviations of viscosity from the ideal additive behaviour of the two salt-solvent binary systems occur at a mole fraction of DMSO in the mixed solvent of 0.3. The observed dependence is discussed in relation to the structure of the solution.

Glass transition temperatures in the system calcium chloride-water-dimethylsulphoxide

The glass-forming composition region of the CaCl2-H2O-DMSO system has been established, and the glass transition temperatures of the mixtures have been determined as a function of the CaCl2 content at a constant DMSO mole fraction in the mixed solvent. The dependence of the glass transition temperature on the CaCl2 mole fraction at a constant mole fraction of DMSO in the mixed solvent can be described by a linear relationship.

Enthalpic and entropic contributions to substituent effects for the ionization of meta- and para-hydroxybenzoic acids in water—dimethylsulfoxide mixtures at 25°C

Separate enthalpic and entropic contributions to substituent effects on the dissociation of m-hydroxybenzoic acid in water—dimethylsulfoxide mixtures ranging from 0.0 to 0.57 mole fraction of DMSO are presented. The effect of the medium on the reaction constant is explained in terms of solute—solvent interactions. The entropy reaction constant values ϱ s of the meta-hydroxy compound are much greater than those of the meta-chloro and nitro compounds in the examined mole fraction range. For the para-hydroxy isomer only a trend of σ s and ϱ s values can be calculated. This fact is due to the electron-releasing resonance effect which overlaps and prevails over the inductive effect.

Thermodynamics of ionization processes for hydroxy-substitute benzoic acids in water—dimethylsulfoxide mixtures at 25°C

The ionization and solution enthalpies of the hydroxybenzoic acids were measured calorimetrically at 25°C in water—dimethylsulfoxide mixtures ranging from pure water to 0.8 DMSO mole fraction. In the same solution, the Δ G° values for the ionization processes have been determined by potentiometric measurements. The different enthalpy solvation values for the three hydroxy isomers were explained taking into account the prevalence of the resonance or the inductive effect as a function of the solvent composition. The intramolecular hydrogen bond of the undissociated molecules seems to be responsible for the greater degree of ionization of o-hydroxybenzoic acid with respect to the m and p-hydroxy isomers.

Study of the effect of the medium on the reaction constants for the dissociation of nitrophenols in water—dimethylsulfoxide mixtures at 25°C

The effect of the medium on the reaction constants of the dissociation of nitrophenols in water—dimethylsulfoxide mixtures ranging from 0.0 to 0.8 mole fraction of DMSO is presented. In this study, use has been made of some linear free energy relationships. For standard reactions, the ionization processes of nitrobenzoic acids, at the same mole fractions, are used. The trend of the three reaction constants is very similar and their values are quite close.

ORTHO effects of chloro- and nitrobenzoic acids in water—dimethylsulphoxide mixtures at 25° C

The dissociation of ortho-chloro- and nitro-benzoic acids in water—DMSO mixtures (0.0 + 0.8 DMSO mole fraction) was studied by means of a linear combination of the ordinary polar, proximity polar, and steric effects. Enthalpic and entropic contributions to substituent effects for the ortho-derivatives were also examined. The dissociation of the ortho-chloro-derivatives appear to be mostly anion-controlled. However, for the ortho-nitro-derivatives, the steric inhibition of solvation on the undissociated molecules may also be involved in controlling the course of the reaction.

Calorimetric study of ionization processes for nitro-substituted phenols in water-dimethylsulfoxide mixtures at 25°C

The ionization and solution enthalpies of the nitrophenol isomers were measured calorimetrically at 25°C in water-DMSO mixtures ranging from pure water up to 0.8 DMSO mole fraction. The different solvation values obtained for ortho-nitrophenol with respect to the meta and para isomers, were explained taking into account the electrostatic forces between the water molecules and the anions, as well as the intramolecular and intermolecular hydrogen bonds associated with the undissociated molecules.