Enthalpies of transfer of acetonitrile from water to aqueous methanol, ethanol and dimethylsulphoxide mixtures at 298.15 K

Previous studies have established that the extended coordination model of solvation can satisfactorily account for the variation in the transfer enthalpies of solutes in mixed-solvent systems. The model parameter relating to the solute-induced disruption of the solvent structure shows a marked dependence on the nature of the mixed solvent. In the present paper we report the transfer enthalpies of acetonitrile from water to aqueous methanol, ethanol and dimethylsulphoxide (DMSO) systems. Analysis of these in terms of the extended coordination model confirms both the model's ability to account for the experimental data, and the variability of the structural disruption parameter. The solvation parameters recovered from the analyses indicate that the net effect of acetonitrile on the solvent structure is a breaking of solvent-solvent bonds. The extent of bond breaking of the solvent increases from MeOH to EtOH.     

Pulse polarographlc behaviour of n-nitrosamines in mixtures of water with methanol and acetonitrile

The half-wave potentials of N-nitrosodiethanolamine,N-nitrosoproline,N-nitrosodiphenylamine and N-nitrosodibutylamine become more negative as the content of the organic solvent is increased. The limiting currents are diffusion-controlled for the first two compounds, but adsorption effects intervene at low concentrations of solvent with the other compounds.     

Kinetics and mechanism of isatin ring opening in aqueous binary mixtures of methanol and acetonitrile cosolvents

Solvent effects on the kinetics of hydrolysis of isatin by sodium hydroxide have been investigated within the temperature range (30–55°C) in methanol-water and acetonitrile-water media of varying solvent compositions up to 70% (v/v) of the organic solvent component. The thermodynamic activation parameters were calculated and discussed in terms of solvation effects. The determined isokinetic temperatures, in both systems, revealed the existence of compensation effect arising from strong solute-solvent interactions; log k was correlated with both log [H₂O] and the reciprocal of the dielectric constant. The first correlation was observed to be linear while the second was nonlinear. Finally a mechanism for the isatin ring opening was proposed, which accounts for the role and the effect of the solvent on the reaction rate. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 463–469, 1998     

One-dimensional model for water and aqueous solutions. III. Solvation of hard rods in aqueous mixtures

A simple one-dimensional model for aqueous solution is applied to study the solvation thermodynamics of a simple solute (here, a hard-rod particle) in mixtures of waterlike particles and a cosolvent. Two kinds of cosolvents are considered, one that stabilizes and one that destabilizes the "structure of water." The results obtained for the Gibbs energy, entropy, enthalpy, and heat capacity of solvation are in qualitative agreement with experimental data on the solvation of argon and methane in mixtures of water and ethanol and of water and p-dioxane.     

Solvation of a hydrogen isotope in aqueous methanol, NaCl, and KCl solutions

The muon hyperfine coupling constant (hfc) of the light hydrogen isotope muonium (Mu) was measured in aqueous methanol, NaCl, and KCl solutions with varying concentrations, in deuterated water, and in deuterated methanol. The muon hfc is shown to be sensitive to the size and composition of the primary solvation shell, and the three-dimensional harmonic oscillator model of Roduner et al. (J. Chem. Phys. 1995, 102, 5989) has been modified to account for dependence of the muon hfc on the methanol or salt concentration. The muon hfc of Mu in the aqueous methanol solutions decreases with increasing methanol concentration up to a mole fraction (chiMeOH) of approximately 0.4, above which the muon hfc is approximately constant. The concentration dependence of the muon hfc is due to hydrophobic nature of Mu. It is preferentially solvated by the methyl group of methanol, and the proportion of methanol molecules in the primary solvation shell is greater than that in the bulk solution. Above chiMeOH approximately 0.4, Mu is completely surrounded by methanol. The muon hfc decreases with increasing methanol concentration because more unpaired electron spin density is transferred from Mu to methanol than to water. The unpaired electron spin density is transferred from Mu to the solvent by collisions that stretch one of the solvents bonds. The amount of spin density transferred is likely inversely related to the activation barrier for abstraction from the solvent, which accounts for the larger muon hfc in the deuterated solvents. The muon hfc of Mu in electrolyte solution decreases with increasing concentration of NaCl or KCl. We suggest that the decrease of the muon hfc is due to the amount of spin density transferred from Mu to its surroundings being dependent on the average orientation of the water molecules in the primary solvation shell, which is influenced by both Mu and the ions in solution, and spin density transfer to the ions themselves.     

Excess enthalpies of binary and ternary mixtures of acetonitrile with methanol,ethanol and benzene

Excess molar enthalpies are measured for the binary mixtures methanol—acetonitrile and ethanol—acetonitrile at 25 and 35°C and for the ternary mixtures methanol—acetonitrile—benzene and ethanol—acetonitrile—benzene at 25°C using an isothermal dilution calorimeter. The binary results are well reproduced with an association model which contains four equilibrium constants for the association of alcohol, two equilibrium constants for that of acetonitrile, and two solvation equilibrium constants between alcohol and acetonitrile molecules. The ternary results are compared with those calculated from the model with binary parameters.     

Comparison of surface states of chemically modified silicas in aqueous acetonitrile and methanol

Summary The thermodynamic behaviour of n-alkylbenzenes on chemically modified silicas in reversed-phase liquid chromatography has been examined in acetonitrile-water and methanol-water systems. Plots of the thermodynamic parameters obtained against the organic solvent compositions indicate an interesting trend which implies that the surface states of the chemically modified silicas under the two eluent systems are different.     

Solvation of iron and chromium complexes in alcohol–water mixtures

Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H₂O and one in MeOH–H₂O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H₂O and t-BuOH–H₂O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H₂O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H₂O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H₂O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H₂O-rich aqueous-alcohol mixtures. Some spectroscopic (¹H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes.     

Electro-kinetic transport of water,methanol and their binary mixtures

Summary Electro-osmosis of water, methanol and their binary mixtures across pyrex membrane has been investigated. Form of the phenomenological equation applicable in the present case has been ascertained. Electrophoretic velocities of pyrex glass particles have also been measured. A simple method for the determination of pore radius of membranes has been suggested.

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Zusammenfassung Es wurde die Elektro-Osmose von Wasser, Methanol und den binären Mischungen derselben an Pyrexmembranen untersucht. Dabei wurde die phänomenologische Gleichung, die auf den vorliegenden Fall anwendbar ist, gesichert. Ergänzend wurden elektrophoretische Wanderungsgeschwindigkeiten von Pyrexglasteilchen gemessen. Außerdem wurde eine einfache Methode zur Bestimmung des Porenradius der Membranen vorgeschlagen.

     

Reactive and non-reactive counterion surfactants in water and aqueous acetonitrile

Rates of hydrolysis of hydroxamic acids with perfluorooctanoic acid as a reactive counterion surfactant and also with sodium sulfonate surfactants plus HCl have been determined in both water and aqueous acetonitrile solvents. The pseudophase ion exchange model satisfactorily explains the micellar effects for both the reactive and non-reactive counterion surfactants in both solvent systems.     

Thermochemical behaviour of crown ethers aqueous organic solvents: Part IV: Propanol and acetonitrile with water mixtures

Enthalpies of solution of 15-crown-5 (15C5) in the mixtures of water with acetonitrile (AN) or propan-1-ol (PrOH) and benzo-15-crown-5 ether (B15C5) in the PrOH-water mixtures have been measured at 298.15 K. The values of standard enthalpies of solution of 15C5 are negative in the mixtures of water with AN within the whole range of mixture composition and in the mixtures water-PrOH for water content x_w>0.1 and those of B15C5 are positive (except the standard enthalpy of B15C5 in pure water) in the system water-PrOH. The results of the calorimetric measurements together with the earlier data for B15C5 in water-acetonitrile mixtures are discussed with regard to the intermolecular interactions that occur in these systems.This revised version was published online in November 2005 with corrections to the Cover Date.     

Reactivity of carbocations from 1,2-dihydroquinolines in binary mixtures of methanol with pentane and acetonitrile

The rate constants and activation parameters of the reactions of the carbocation resulting from 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline photolysis with methanol (k ₁) and the methoxide ion (k ₂) have been measured by flash photolysis in binary mixtures of methanol with inert solvents (nonpolar pentane and polar acetonitrile) in wide composition ranges. The changes in the activation parameters for k ₁ at different solvent compositions show that the increase in the rate constant in the pentane mixtures is mainly deter-mined by the increase in the preexponential factor. The decrease in k ₁ in the acetonitrile mixtures is deter-mined by the decrease in the methanol concentration and by the increase in the activation energy. The different roles of the methoxide ion in the reaction are demonstrated. They depend on the nature of the inert solvent in the mixture. The results of this study are considered in terms of methanol clustering in pentane and acetonitrile, the different solubilities of 6-ethoxy-1,2,2,4-tetramethyl-1,2-dihydroquinoline in the components of the binary mixtures, and the difference in distribution and solvation between the carbocation and the methoxide ion in the mixtures.     

Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile

We present results of the theoretical study and numerical calculation of the dynamics of molecular liquids based on the combination of the memory equation formalism and the reference interaction site model (RISM). Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density (pressure) dependence of translational diffusion coefficients D and orientational relaxation times tau for acetonitrile in water, methanol in water, and methanol in acetonitrile--all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the extended simple point charge model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and tau observed in real and computer experiments. In particular, anomalous behavior, i.e, the increase in mobility with density, is observed for D and tau of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.     

Solvation and hydrophobic hydration of different types of alkylamines inN,N-dimethylformamide and water mixtures

Enthalpies of solution of twelve amines of different type have been determined at 25°C in mixtures of N,N-dimethylformamide and water over the whole composition range. The enthalpies of transfer from water to the mixtures deviate substantially from a linear dependence on the mole fraction of water. These deviations appear to contain additive contributions of the different alkyl groups. By application of a simple hydration model the enthalpic effect of hydrophobic hydration has been calculated for each amine. For alkylamines this is determined by the number and size of the alkyl groups present in the molecule. The contribution of each alkyl group is the same in primary, secondary and tertiary amines. Results for the different alkyl groups show a close relationship with values for alcohols obtained previously. Differences between alcohols and amines can be attributed to differences in the hydrophobic hydration of the parts of the solute molecules which are adjacent to the polar group. The influence of the polar group does not seem to extend beyond the second carbon atom.     

On separating mixtures containing methanol, tetrahydrofuran, and water by distillation

The results of calculations according to NRTL model of phase equilibrium of a binary system of THF-methanol and ternary system THF-methanol-water were demonstrated.     

Polyol-induced partitioning of essential oils in water/acetonitrile solvent mixtures

Polyol-induced extraction (PIE) is applied to the extraction of essential oils, using glycerol as a mass separating agent. In 1:1 acetonitrile (ACN)/water solvent mixtures, two immiscible phases can be generated. PIE as an alternative extraction technique was assessed by the extraction of the main flavor and fragrance compounds that comprise six essential oils. In the extraction of eugenol (4-allyl-2-methoxyphenol) from clove buds, the partition coefficients were determined and the % recovery and thermodynamic data in the temperature range of ?20 to 20°C were calculated. The main components present in each essential oil extract were identified through gas chromatography/mass spectrometry (GC/MS) and the compositional profile was compared to traditional extraction techniques. The optimized extraction conditions (?10°C, 1:1 ACN/water (v/v), 20% glycerol) for eugenol at ?10°C give a partition coefficient (K_PC) of 87 and an extraction efficiency of 97% in the acetonitrile-rich phase. The eugenol migration to the organic phase is a spontaneous process (ΔG°?=??9.3?kJ/mol) and an endothermic process (ΔH°?=?9.2?kJ/mol) with entropy being the driving force behind the reaction (ΔS°?=?70?J/K, TΔS°?=?18.4?kJ). The technique was applied to five other essential oils (cinnamon bark, caraway seed, spearmint leaf, peppermint leaf, and anise seed oils) with similar results.     

Electrochemical study of potassium and iodide ions resolvation in aqueous methanol mixtures

The results from the compensating voltage measurements of Volta circuits by the Kenrik method at 298.15 K were used to calculate the real primary media effect of potassium and iodide ions and real Gibbs energy of K⁺ and I⁻ transfer from water to aqueous methanol (MeOH) mixed solvent. The surface potential $\Delta \chi _{H_2 O}^{MeOH} $\Delta \chi _{H_2 O}^{MeOH} at non-aqueous solvent/gas interface was found. This value was used to calculate the chemical thermodynamic characteristics of the studied ions. The solvation features of the studied ions were revealed in the aqueous methanol mixed solvent.     

Solvation and solvatochromism in CO2-expanded liquids. 1. Simulations of the solvent systems CO2 + cyclohexane, acetonitrile, and methanol

Molecular dynamics simulations of CO(2)-expanded cyclohexane, acetonitrile, and methanol are reported at various compositions along the experimental bubble-point curve at 298 K. Simulated properties include energies, local compositions, viscosities, diffusion coefficients, and dielectric constants and relaxation times. On the basis of the limited comparisons to experimental data currently available, the results indicate that simple intermolecular potential models previously developed for simulating the pure components provide reasonable representations of the energetics and dynamics of these gas-expanded liquids.