Whole Range Of Solvent Composition Research Articles

VOLUMETRIC AND VISCOMETRIC DETERMINATION OF BINARY LIQUID MIXTURES OF 2-ETHOXYETHANOL AND AMYL ACETATE AT TEMPERATURES OF (298.15 AND 303.15) K

Densities and viscosities have been determined at temperatures of (298.15 and 303.15) K for binary liquid mixtures of 2-ethoxyethanol with amyl acetate over the entire range of solvent composition. From the experimentally determined values, excess molar volume, VE, excess viscosity, ηE and excess Gibbs free energy of activation of viscous flow, G*E have been calculated. These calculated excess thermodynamic functions were fitted to Redlich-Kister polynomial equation to obtain the fitting coefficients and standard deviations. The values of excess molar volume, VE were negative and that of the excess viscosities, ηE were found to be positive, while excess Gibbs free energy of activation of viscous flow, ΔG*E were negative over the whole range of solvent composition for the binary systems at the studied temperatures. The behavior of these excess functions with composition of the mixtures have been discussed in respect of molecular interactions between the components of liquid systems. The mixture viscosities were correlated using empirical relations like Grunberg-Nissan, Frenkel, Hind, Wijk and Kendall-Monroe model equations. Comparison of these interaction parameters have been engaged to explain the intermolecular interactions between the alkoxy alcohol and the ester.

Hydrogen bonding in protic and aprotic amide mixtures: Low-frequency Raman spectroscopy, small-angle neutron scattering, and molecular dynamics simulations

The hydrogen-bonding interactions in protic and aprotic amide solvent mixtures, i.e., formamide (FA) and N,N-dimethylformamide (DMF), were investigated via low-frequency Raman spectroscopy, small-angle neutron scattering (SANS) experiments, and molecular dynamics (MD) simulations. In a neat amide system, the low-frequency Raman spectra R(ν)s were well reproduced by the corresponding S(ν) spectra derived from the MD simulations. The observed peaks in R(ν)s at around <200cm−1 were assigned to the intermolecular interactions, particularly in terms of the hydrogen-bonding network formation and its dimensionality in the liquid state. The SANS experiments for the FA–DMF mixtures demonstrated that the FA molecules forming an extended three–dimensional hydrogen-bonding structure in the neat system interacted with DMF molecules through the hydrogen bonds in the mixtures over the whole range of solvent compositions, resulting in a homogeneous mixing state. Additionally, the R(ν) spectra for the mixtures were represented by the corresponding S(ν) spectra. From the R(ν) and S(ν) spectra of the FA–DMF mixtures, we found that (1) the Raman band at around 110cm−1 mainly originates from the libration mode of amide molecules in the chain-like hydrogen-bonded structure and (2) the higher frequency band (approximately 200cm−1) was attributed to the libration of the FA molecule restricted by the three-dimensional hydrogen-bonded network, which remained even in the DMF-rich compositions.

Local structure and translational dynamics of NMF (N-methylformamide)–DMF (N,N-dimethylformamide) mixtures, via molecular dynamics simulation

In this work, the liquid amide mixture of N-methylformamide (NMF) with N,N-dimethylformamide (DMF) has been investigated by means of the molecular dynamics simulation method. The intermolecular structure and local mole fractions around any kind of the component molecules have been studied in terms of the calculated site-site correlation functions at three solvent compositions, XDMF, and ambient conditions. The hydrogen bonding network of the system has been extensively explored and the several hydrogen bond types formed between NMF-NMF, DMF-DMF and NMF-DMF in each mixture per molecule have been obtained with increasing XDMF. The results obtained reveal the notable effect of DMF molecules upon the formation of the hydrogen bonding network in each system. The investigated diffusion coefficients of both mixture components show clearly a linear increase of the diffusivity of all molecules while the DMF fraction increases. The intermolecular structure and hydrogen bonding properties studied validate the results from previous small angle neutron scattering studies on the system and support their conclusion that this amide mixture may be considered as an almost ideal one. Also, it may be concluded that DMF does not self-aggregate, because it acts as a hydrogen-bond breaker over the whole range of solvent composition. This finding is in accordance with the translational diffusive behavior of the molecules in the mixtures mentioned above. The detailed analysis of the hydrogen bonding network in DMF- rich and NMF-rich mixtures has revealed important information regarding the short range molecular aggregation in these diluted mixtures. This result is in general found to be comparable with corresponding predictions from previous experimental low-frequency raman spectroscopic studies of these mixtures.

Comparative conductimetric studies of salicylic acid in methanol-water mixtures at 25 °C

The conductivity of salicylic acid in methanol-water mixtures was measured at 25 °C. Experimental data were analyzed using the Hsia-Fuoss and Fuoss-78 conductance equations and a comparison was made. The Hsia-Fuoss and Fuoss-78 methods were also used to deter-mine the thermodynamic association constants and the limiting molar conductivities for all solvent compositions. The limiting equivalent conductance decreases with an increase in the methanol content in the binary mixtures over the whole range of solvent compositions, but the variation does not give a constant value of Walden product. The electrolytes were found to be practically completely associated in all solvent mixtures studied. The association constant of salicylic acid decreases as the dielectric constants of the mixtures increase.

Modeling Preferential Solvation in Ternary Solvent Systems

The theoretical solvent exchange model of Bosch and Rosés for binary solvents was extended to ternary solvent mixtures. The model was applied to ENT values for the mixture methanol/1-propanol/acetonitrile, in terms of 48 new values in a total of 79, measured at 25 degrees C over the whole range of solvent compositions. It was also applied to the mixture methanollethanol/acetone at the same temperature using 93 E(N)T values obtained from literature. Very good fits between experimental and calculated values, substantiated by external validation methods, were achieved for both sets of data. The use of the developed extended model allowed the interpretation of measured solvatochromic shifts in terms of solute-solvent and solvent-solvent interactions in the local environment of the solute's dye for the two ternary systems and the underlying binary mixtures. It also provided the identification of various complex solvent entities and the quantification of their relative concentrations in the probe's cybotactic region, thus leading to new and significant physicochemical insights at a molecular level, regardless of the nonconsideration of the formation of solvent complexes in the bulk. Results clearly showed a different solvent composition in the vicinity of the solute. The further extension of the model to four and five components is also presented.

A kinetic model for water reactivity (avoiding activities) for hydrolyses in aqueous mixtures – selectivities for solvolyses of 4‐substituted benzyl derivatives in alcohol–water mixtures

AbstractFor solvolyses of various benzyl substrates in ethanol–water (EW) and methanol–water (MW) mixtures, product selectivities (S) are reported for chlorides at 75 °C defined as follows using molar concentrations: S = ([ether product]/[alcohol product]) × ([water]/[alcohol solvent]). The results support earlier evidence that solvolyses of 4‐nitrobenzyl substrates are SN2 processes, which are not susceptible to mechanistic changes over the whole range of solvents from water to alcohol. S values at 25 and/or 45 °C in EW and MW, and additional kinetic data including kinetic solvent isotope effects (KSIE) are reported for solvolyses of 4‐nitrobenzyl mesylate and tosylate. A kinetic model, explaining both rates and product, is proposed; a general medium effect due to solvent polarity is combined in one parameter with solvent effects on the nucleophilicity of the water and alcohol molecules acting as nucleophiles in SN2 reactions. According to this model, as alcohol is added to water the rate of reaction decreases due to a decrease in solvent polarity, but the nucleophilicity of water increases relative to alcohol. The availability of experimental rate and product data over the whole range of solvent compositions from alcohol to water, reveals limitations of alternative approaches using activities. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Enthalpies of Transfer of Tetraalkylammonium Bromides and CsBr from water to Aqueous DMF at 298.15 K

Enthalpies of transfer of tetraalkylammonium bromides and CsBr from water to aqueous DMF mixtures are reported and analyzed in terms of a new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using a new solvation theory to model the enthalpies of transfer shows excellent agreement between experimental and calculated values over the entire range of solvent compositions. The analyses show that tetrapropylammonium bromide, Pr4NBr, and tetrapentylammonium bromide, Pen4NBr, are preferentially solvated by water; in contrast tetrabutylammonium bromide, Bu4NBr, is preferentially solvated by DMF. The solvation of tetramethylammonium bromide, Me4NBr, and cesium bromide, CsBr, is random. The extent to which the tetraalkylammonium bromides disrupt solvent–solvent bonds increases systematically in going from Me4NBr to Pen4NBr.

Solvation of Cobalt(II) Ion in N,N-Dimethylformamide–Methanol Mixed Solvent: Calorimetry and VIS Spectroscopy Studies

The enthalpies of solution of Co(II) and Na(I) trifluoromethanesulfonates (triflates) in N,N-dimethylformamide (DMF)–methanol (MeOH) mixtures have been measured over the whole range of solvent composition. From these data the enthalpies of transfer of Co(II) and triflate ions from methanol to the mixed solvent have been determined usingliterature values of the enthalpies of transfer of the Na+ ion. The results have been analyzed by means of the theory of preferential solvation. The analysis revealed the preference of DMF for solvating the Co(II) ion in the MeOH-rich region of solvent composition and the lack of preference of any component in the DMF-rich region. Visible absorption spectra of the Co(II) ion in DMF–MeOH mixtures have been also measured in the whole range of solvent composition and analyzed using the partial least-squares method. The mean composition of the solvation sphere of the Co(II) ion versus solvent composition has been determined on the basis of both analyses. The results were found to be consistent with each other and with those obtained previously from FT-IR spectra.

Bubble sizes in agitated solvent/reactant mixtures used in heterogeneous catalytic hydrogenation of 2-butyne-1,4-diol

Catalytic hydrogenations reactions are frequently conducted in “dead-end” multiphase stirred reactors with the reactant dissolved either in an alcohol, or in water or a mixture of the two. In such systems, the rate of gas–liquid mass transfer, which depends on bubble size, may well be the overall rate-limiting step. However, a study of bubble sizes across the whole range of solvent compositions from entirely water to entirely organic has not been reported. Here, for the first time, a systematic investigation has been made in a 3 L, closed vessel simulating a “dead-end” reactor containing 1% by volume of air which is dispersed by a Rushton turbine in water, isopropanol (IPA) and mixtures of the two, with and without 2-butyne-1,4-diol simulating a reactant. Mean specific energy dissipation rates, ε ¯ T , up to 50 W kg - 1 have been used and bubbles size distributions and mean size were measured using a video–microscope–computer technique. In the single component solvents (water, σ ∼ 72 mN m - 1 ; IPA, σ ∼ 21 mN m - 1 ) though the interfacial tensions are very different, irregular, relatively large bubbles of similar sizes were observed ( d 32 ∼ 300 μ m in IPA, and d 32 ∼ 400 μ m in water) with a wide size distribution. In the mixed aqueous/organic solvents, and especially at the lower concentrations of IPA (1%, 5%, 10%), the bubbles were spherical, much smaller ( d 32 from 50 to 70 μ m ) with a narrow size distribution. The addition of the reactant (0.2 M 2-butyne-1,4-diol) to the mixed solvents had little effect on the mean size, shape or distribution. However, addition to water (thus producing a mixed aqueous/organic liquid phase) led to small ( d 32 ∼ 50 μ m ) spherical bubbles of narrow size distribution. Neither Weber number nor surface tension was suitable for correlating bubble sizes since σ decreased steadily from pure water to IPA whilst bubble size passed through a minimum at around 5% IPA. For any particular fluid composition, the functionality between d 32 and ε ¯ T was similar, i.e. d 32 ∝ ( ε ¯ T ) - 0.25 . The above observations are explained in terms of the polarisation of bubble surfaces in miscible mixed aqueous/organic liquids caused by preferential directional adsorption at low concentrations of the organic component with its hydrophilic part directed into the aqueous phase and its hydrophobic part into the gas phase. As a result, coalescence is heavily suppressed in the low-concentration miscible alcohol (or diol)/aqueous systems whilst strong coalescence dominates bubble sizes in water and the alcohol and at high concentrations of the latter.

Solvation of cobalt(II) and trifluoromethanesulfonate ions in N, N-dimethylformamide–methanol mixed solvent studied by means of FT-IR spectroscopy

FT-IR spectra of Co(CF 3SO 3) 2– N, N-dimethylformamide (DMF)–methanol (MeOH) solutions have been measured over the whole range of solvent composition. The data together with the obtained previously spectra of DMF–MeOH mixtures have been analyzed using the difference spectra method in the region of CO and OH stretching bands. The number of DMF and MeOH molecules in the first solvation sphere of Co(II) ion versus solvent composition has been determined. The second solvation sphere has been revealed and characterized quantitatively. Solvation of trifluoromethanesulfonate (triflate) ion as well as ion association in DMF solution have been also studied.

A new equation to reproduce the enthalpies of transfer of formamide, N-methylformamide and N, N-dimethylformamide from water to aqueous methanol mixtures at 298 K

The enthalpies of transfer of formamide (Form) N-methylformamide (NMF) and N, N-dimethylformamide (DMF) from water to aqueous methanol mixtures are reported and analysed in terms of the new solvation theory. It was found that a previous equation could not reproduce these data over the whole range of solvent compositions. Using the new solvation theory to reproduce the enthalpies of transfer shows excellent agreement between the experimental and calculated data over the entire range of solvent compositions. The analyses show that the solvation of DMF is random in the aqueous methanol mixtures while Form and NMF are preferentially solvated by methanol. It is also found that the interaction of the solutes is stronger with methanol than with water.

Liquid Structure and Preferential Solvation of Metal Ions in Solvent Mixtures of N,N-Dimethylformamide and N-Methylformamide

Raman spectra of aprotic N,N-dimethylformamide (DMF) and protic N-methylformamide (NMF) mixtures containing manganese(II), nickel(II), and zinc(II) perchlorate were obtained, and the individual solvation numbers around the metal ions were determined over the whole range of solvent compositions. Variation profiles of the individual solvation numbers with solvent composition showed no significant difference among the metal systems examined. In all of these metal systems, no preferential solvation occurs in mixtures with DMF mole fraction of x(DMF) < 0.5, whereas DMF preferentially solvates the metal ions at x(DMF) > 0.5. The liquid structure of the mixtures was also studied by means of small-angle neutron scattering (SANS) and low-frequency Raman spectroscopy. SANS experiments demonstrate that DMF molecules do not appreciably self-aggregate in the mixtures over the whole range of solvent composition. Low-frequency Raman spectroscopy suggests that DMF molecules are extensively hydrogen-bonded with NMF in NMF-rich mixtures, whereas NMF molecules extensively self-aggregate in DMF-rich mixtures, although the liquid structure in neat NMF is partly ruptured. The bulk solvent structure in the mixtures thus varies with solvent composition, which plays a decisive role in developing the varying profiles of the individual solvation numbers of metal ions in the solvent mixtures.

Critical validation of a new simpler approach to estimate aqueous p Ka of drugs sparingly soluble in water

A simple linear approach to estimate the aqueous p K a of compounds sparingly soluble in water, mainly drugs, from solely one p K a value determined in any methanol/water mixture is evaluated. The parameters (slope and intercept) of the linear relationships are related to the solvent composition and can be easily calculated according to the acidic or basic functional group of the compound. The method has been tested using the available literature data for phenols, aliphatic carboxylic acids, benzoic acid derivatives, both ortho and non- ortho substituted, amines and imidazole derivatives. The study involves the whole range of solvent composition and about one hundred compounds which show a wide variety of aqueous p K a, from 1.3 to 12.4. The differences between calculated and previously published aqueous p K a values are less of 0.2 pK units. Consistent values are obtained whatever the composition of methanol/water mixture employed in the experimental measurements. The results support the usefulness of the tested method as a very simple approach to get reliable aqueous p K a values for sparingly soluble drugs.

MD Simulation Studies of Selective Solvation in Methanol−Water Mixtures: An Effect of the Charge Density of a Solute

MD simulations have been performed for NaCl, NaI, and fictitious solutions of discharged counterparts of Na+ and Cl- ions to investigate an effect of the charge density of a solute on its solvation in methanol−water mixtures. Solvent−solvent interactions have been described in terms of flexible models, whereas solutes have been considered as charged or uncharged Lennard-Jones spheres. An analysis of solvation shells has been based on radial distribution functions, angular distributions, coordination numbers, and residence times of solvent molecules. Preferential solvation of anions by methanol molecules becomes less pronounced with decreasing charge density of a solute and vanishes for the discharged chloride ion. In contrast to preferential hydration of Na+ in water deficit solvents, its uncharged counterpart Na0 is preferentially solvated by methanol molecules over the whole range of solvent composition. Results for NaCl solution have been compared with those obtained with ab initio ion−solvent potentials and the same model of solvent molecules. The type of ion−solvent potential has small effect on the structure and composition of ionic shells, but its influence on the persistence of the coordination shells is more noticeable.

Mesoscopic segregation in binary liquid solutions: application of a model for block copolymers to non-macromolecular systems

In this work, an analogy between block copolymer phase behaviour and microdomain spacial organization in certain liquid organic/aqueous binary systems is discussed. The peculiar phase behaviour in block copolymers has been described by a segregation of the constituting blocks in domains of mesoscopic dimensions that do not lead to actual macroscopic phase separation, in contrast to what is observed in ordinary binary polymer mixtures. In the liquid non-macromolecular systems under investigation here, such events can be described as a self-association of the organic moiety leading to the formation of initially spherical microdomains that grow in size and progressively change their geometry into interpenetrating patterns, as one proceeds towards composition regions of low water content, until a collapse of the microdomains is reached, and a non-polar continuum is produced. At that point, a reversion in the microconfiguration of the binary mixture takes place. In this work, vibrational spectroscopic data for one of those systems, namely, tetramethylurea/water, were analysed in order to determine changes in structural/dynamic parameters throughout the whole range of solvent composition, with the aim of allowing inferences relative to organization patterns of the micro/meso-domains. Along with evidence from previous work, the results strongly suggest a close parallelism between phase behaviour in these non-macromolecular liquid systems and that observed for block copolymers.

Characterization of solvent mixtures. Part 8 — preferential solvation of chemical probes in binary solvent systems of a polar aprotic hydrogen-bond acceptor solvent with acetonitrile or nitromethane. Solvent effects on aromatic nucleophilic substitution reactions

The use of chemical probes for the characterization of chemical properties was explored for completely non-aqueous aprotic binary solvent mixtures. The Dimroth–Reichardt ET(30) betaine dye, 4-nitrophenol, 4-nitroanisole, 4-nitroaniline and N,N-diethyl-4-nitroaniline were used to study preferential solvation in binary mixtures of a polar aprotic hydrogen bond-acceptor solvent (DMSO, DMF, acetone, butanone and ethyl acetate) with acetonitrile or nitromethane at 25 °C over the whole range of solvent composition. The indicators were employed to determine ET(30), π*, α and β solvatochromic parameters of the mixtures. Each solvent system was analysed according to its deviation from ideal behaviour due to the preferential solvation of the indicators and also from the complicated intermolecular interactions of the mixed solvent. The validity of the concept of an intrinsic, absolute property of a solvent mixture and whether such a property can be defined by means of chemical probes is discussed. These results were related to the solvent effects on some aromatic nucleophilic substitution reactions. The kinetics of the reactions between 1-fluoro-2,4-dinitrobenzene and primary or secondary amines were studied in ethyl acetate– acetonitrile and N,N-dimethylformamide–acetonitrile mixtures, respectively, taken as representatives of two clearly different solvation models. Copyright © 1999 John Wiley & Sons, Ltd.

Solute–solvent and solvent–solvent interactions in binary solvent mixtures. Part 4. Preferential solvation of solvatochromic indicators in mixtures of 2-methylpropan-2-ol with hexane, benzene, propan-2-ol, ethanol and methanol

The solvatochromic shifts of several indicators {2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)-1-phenolate [Reichardt’s ET(30) betaine dye], 4-nitroanisole, 4-nitroaniline and N,N-diethyl-4-nitroaniline} have been measured in binary mixtures of propan-2-ol with hexane, benzene, ethanol and methanol at 25 °C over the whole range of solvent composition. From the UV–VIS spectroscopic data the preferential solvation of the indicators has been studied. The solvatochromic parameters ET(30), π*, α and β of the binary solvent mixtures studied have been calculated from the solvatochromic shifts.

Effect of the solvent composition and of the addition of 15-Crown-5 on the conductance of lithium picrate and lithium perchlorate in acetonitrile + nitromethane mixtures

Abstract Conductivity data for lithium picrate and lithium perchlorate in acetonitrile + nitromethane isodielectric mixtures at 25°C are reported. Treatment of the data in terms of the Fuoss 1980 equation shows that the ion pair association of these electrolytes depends strongly on the composition rather than on the macroscopic dielectric constant of the solvent. Such a result has been rationalized in terms of specific ion-solvent interactions, related to the peculiar properties of the acetonitrile + nitromethane mixtures. The effect of the complexation of lithium ion with 15 crown (15C5) on the ionization of both electrolytes was also investigated. The results show that the shielding of the electric field between the lithium ion and counterion, caused by the crown ether, reduces drastically the ion pairing. The association constants for each electrolyte in the ternary system acetonitrile + nitromethane + 15C5 become, in addition, of the same order of magnitude in the whole range of solvent composition, as expected for isodielectric solvent mixtures.

Effects of solvents on the cobalt phthalocyanine-catalyzed oxidation of hydrophobic thiols

The use of organic solvents in the oxidation of 1-dodecanethiol, catalyzed by cobalt (II) phthalocyanine-tetrasodiumsulfonate (CoPc(NaSO 3) 4) 2,4-ionene , drastically influences the reaction mechanism. Without an organic solvent the reaction proceeds at the thiol-water phase boundary, where the ionene interacts with the negatively charged 1-dodecanethiol droplets. The degree of complexation between the 2,4-ionene and the thiolate anions diminishes when apolar solvents, like toluene, are added. This leads to a tremendous shift of the N + Co ratio, which is a measure of the optimal ionene CoPc(NaSO 3) 4 ratio, from 1250 to 15. Only the maximal catalytic activity is dependent on the amount of apolar solvent used over the whole range of solvent compositions. It is proposed that the reaction proceeds at the phase boundary, but the degree of complexation between the quaternary ammonium groups of the ionene and the thiolate anions decreases with addition of an apolar solvent. The low optimal N + Co ratio of about 15 is apparently sufficient for both binding the ionene to the droplet surface as well as for stabilizing the active dimeric form of the catalyst. When water-insoluble more polar solvents such as 1-octanol are used, the opposite phenomenon is observed: the optimal 2,4-ionene concentration rises. In the latter situation the 2,4-ionene is still able of interacting strongly with the thiolate anions present at the interface of the droplets.

Solvation of cobalt(II) and perchlorate ions in binary mixtures of donor solvents

The enthalpies of solution, (ΔsH°) of sodium perchlorate have been measured in binary mixtures of water with methanol (MeOH), N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) over the whole range of solvent composition. The data and the literature enthalpies of transfer, (ΔtH°), for sodium ion in these mixtures and for perchlorate ion in water–N,N-dimethylacetamide (DMA) mixtures have been used to determine the ionic contributions to the previously reported enthalpies of transfer for cobalt(II) perchlorate from water to the binary mixtures. The results have been compared with the enthalpies of transfer of cobalt(II) and perchlorate ions from water to AN–H2O mixtures and from DMSO to AN–DMSO mixtures, presented earlier (AN, acetonitrile). The ionic transfer data have been discussed in terms of the donor properties and the bulk structure of the binary mixtures investigated.