Mole Fraction Of Acetonitrile Research Articles

Performance of Some Novel Mixed Solvents as Entrainers for Separation of Water and Acetonitrile

Performance of some novel mixed solvents as entrainers was tested for acetonitrile dehydration by extractive distillation. The mixed solvents are composed of ethylene glycol (EG) and choline chloride (ChCl) (EG + ChCl 8:1, EG + ChCl 4:1, EG + ChCl 2:1, and EG + ChCl 4:3), ethylene glycol (EG) and glycerol (EG + glycerol 1:1, EG + glycerol 1:2, EG + glycerol 1:4, and EG + glycerol 1:6), and dimethyl sulfoxide (DMSO) and ChCl (DMSO + ChCl 14:1). Isobaric vapor–liquid equilibrium (VLE) data were measured at 101.3 kPa and at a solvent-free acetonitrile mole fraction of 0.95 for the quaternary systems of water + acetonitrile + EG + ChCl, water + acetonitrile + EG + glycerol, and water + acetonitrile + DMSO + ChCl and for the ternary system of water + acetonitrile + DMSO. The NRTL equation was used for the correlation of the experimental VLE data. For all the three quaternary systems and one ternary system, the mean absolute deviations of equilibrium temperature were no more than 0.33 K, and the mean absolute deviations of water and acetonitrile vapor phase mole fractions were no more than 0.0026 and 0.0047, respectively. The mixed solvent EG + ChCl 4:3, which is also a deep eutectic solvent, showed favorable solvent performance. The azeotrope of water + acetonitrile can be removed at a solvent mass fraction of 0.212 or a solvent mole fraction of 0.104. This amount is less than that of EG (0.367 in mass fraction and 0.227 in mole fraction), EG + glycerol 1:6 (0.341 in mass fraction and 0.195 in mole fraction), and DMSO + ChCl 14:1 (0.266 in mass fraction and 0.153 in mole fraction).

Salting out in ACN/water systems: Hofmeister effects and partition of quercetin

In order to obtain a better understanding of the interaction between acetonitrile and secondary plant metabolites, partition behavior of quercetin as a biomolecule model was investigated in systems composed of acetonitrile, salt [NaCl/KCl/NaBr/KBr], and water at different temperatures. The salting-out ability of the constituent anions and cations of these salts followed the well-known Hofmeister series and the effect of anion was more pronounced than the effect of cation. The Setschenow-type equation is applied to study the slating-out effects on the selected systems. The effect of temperature on the cloud-points as a function of acetonitrile mole fraction was studied in the temperature range of 293.15–328.15 K at 5 K intervals in aqueous solution of acetonitrile. The results showed that the concentration of acetonitrile in equilibrium with a certain concentration of salts significantly increased by the increasing of temperature. The free energy, enthalpy and entropy changes of clouding point (CP) was estimated by using a simple method and the driving force of formation of two phases may be the decrease of enthalpy. Investigation of the distribution behavior of quercetin showed that with increasing the salting-out ability of salt, IC50 values (the concentration necessary for 50% reduction of DPPH) of bottom phases, partition coefficient and recovery of quercetin significantly increased. The effect of temperature on the recovery of quercetin showed that the recovery decreased with the increasing of temperature in total systems under investigation and the decrease more significantly for bromide salts. The change in Gibbs energy (ΔGt), enthalpy (ΔHt) and entropy (ΔSt) of quercetin transfer process was calculated from the partition data. The results confirmed that under the same conditions with increasing the salting-out ability of salt, the calculated ΔGt values were more negative.

3-Methyl-6-nitroindazole in some aqueous co-solvent mixtures: Solubility determination, preferential solvation and solvent effect analysis

The equilibrium solubility of 3-methyl-6-nitroindazole in co-solvent mixtures of acetonitrile (1) + water (2), ethanol (1) + water (2) and n-propanol (1) + water (2) is reported. Experiments were performed by using the saturation shake-flask technique at temperature range from 278.15 to 328.15 K. The maximum solubility value was observed in neat acetonitrile (ethanol or n-propanol) for each co-solvent mixtures. By using the Jouyban-Acree model, the 3-methyl-6-nitroindazole solubility was well correlated obtaining RAD values smaller than 4.50% and RMSD values smaller than 3.36 × 10−4. Quantitative values for the local mole fraction of acetonitrile (ethanol, n-propanol, DMF or acetone) and water around the 3-methyl-6-nitroindazole were computed by using the Inverse Kirkwood–Buff integrals method applied to the solubility data. 3-Methyl-6-nitroindazole was preferentially solvated by water in water-rich compositions; while within co-solvent-rich and intermediate compositions, 3-methyl-6-nitroindazole is preferentially solvated by acetonitrile (ethanol, n-propanol, DMF or acetone) in the acetonitrile (ethanol, n-propanol, DMF or acetone) + water mixtures. The experimental solubility data were correlated by Kamlet and Taft linear solvation energy relationships to examine the main factors describing solvent effect. The results showed that the change in cavity formation energy over the composition played the main role on the solubility variation of 3-methyl-6-nitroindazole in all aqueous mixtures.

Electrochemical Properties of LiAsF6 Solutions in Propylene Carbonate—Acetonitrile Binary Mixtures

Conductivity of LiAsF6 solutions in propylene carbonate—acetonitrile binary mixtures containing 0.2 to 1.4 mol/kg of ionophore is measured at temperatures of 283.15, 293.15, 303.15, and 313.15 K throughout the mixed solvent entire composition range. Concentration dependences of the system’s conductivity can be described by the Casteel—Amis equation, except the lithium hexafluoroarsenate solution in acetonitrile. The activation energy of the charge transfer process in the studied solutions is determined; the LiAsF6 solution in acetonitrile has the lowest activation energy. From conductometry measurements in dilute solutions, the electrolyte limiting molar conductivity is calculated using the Lee—Wheaton equation. The LiAsF6 ionic association in the propylene carbonate—acetonitrile mixtures with the acetonitrile mole fraction from 0.2093 to 0.9006 is not observed; the salt is fully dissociated over this concentration range. The electrochemical stability range for 0.5 mol/kg LiAsF6 in the propylene carbonate—acetonitrile mixture was determined by means of voltammetry at 298.15 K. The decomposition potentials in the cathodic region are due to lithium electro-deposition; they depend on ion—molecule and intermolecular interactions in the system; the anodic decomposition potentials are associated with the solvent oxidation.

Influence of High pH on the Organization of Acetonitrile at the Silica/Water Interface Studied by Sum Frequency Generation Spectroscopy.

The acetonitrile-water mixture is one of the most commonly used solvents in hydrophilic interaction chromatography, which contains silica as the solid phase. As such, the silica/acetonitrile-water interface plays a large role in the separation of compounds. Varying the pH is one way to influence retention times, particularly of ionizable solutes, yet the influence of high pH is often unpredictable. To determine how the structure of this interface changes with pH, we utilized the surface specific technique sum frequency generation (SFG). Previous SFG studies at neutral pH have suggested the existence of acetonitrile bilayers at the aqueous silica interface even at low acetonitrile mole fractions. Here we find that the SFG signal from 2900 to 3040 cm-1 at the silica/acetonitrile-water interface increased as we adjusted the aqueous pH from near neutral to high values. This increase in signal was attributed to a greater amount of aligned water which is consistent with an increase in silica surface charge at high pH. In contrast, complementary measurements of the silica/acetonitrile-deuterium oxide interface revealed that the acetonitrile methyl mode nearly vanished as the aqueous pH was increased. This loss of methyl mode signal is indicative of a decrease in the number density of acetonitrile molecules at the interface, as orientation analysis indicates no significant change in the net orientation of the outer leaflet of the acetonitrile bilayer over the pH range studied.

Determination of spectrophotometric protonation constant of cholinesterase inhibitors

The protonation constant (pKa) of rivastigmine, galantamine and donepezil which are cholinesterase inhibitors used in cure of Alzheimer's disease in acetonitrile-water binary mixtures were determined at 25 oC in ionic strength by spectrophotometric method. Spectra of the drugs were recorded with 1 nm resolution over the 200 to 400 nm interval. Data assessment was carried out with the STAR software program to calculate molar absorbances and stability constants of the compounds studied. Aqueous protonation constant of these compounds were calculated from determined through linear relationship between the mole fraction of acetonitrile and the pKa values and the Yasuda-Shedlovsky equality. The pKa values of inhibitors at 25°C were converted to values at 37°C, without extra estimation. The predicted and calculated pKa values were compared with literature values.

Solvation Structure of 1,3-Butanediol in Aqueous Binary Solvents with Acetonitrile, 1,4-Dioxane, and Dimethyl Sulfoxide Studied by IR, NMR, and Molecular Dynamics Simulation.

The solvation structure of 1,3-butanediol (1,3-BD) in aqueous binary solvents of acetonitrile (AN), 1,4-dioxane (DIO), and dimethyl sulfoxide (DMSO) at various mole fractions of organic solvent xOS has been clarified by means of infrared (IR) and 1H and 13C NMR. The change in the wavenumber of O-H stretching vibration of 1,3-BD in the three systems suggested that water molecules which are initially hydrogen-bonded with the 1,3-BD hydroxyl groups in the water solvent (xOS = 0) are more significantly replaced by organic solvent molecules in the order of DMSO ≫ DIO > AN. This agrees with the order of the electron donicities of the organic solvents. The 1H and 13C chemical shifts of 1,3-BD also revealed the most remarkable replacement of water molecules on the hydroxyl groups by DMSO. In contrast to the DMSO system, the O-H vibration band of 1,3-BD in the AN and DIO systems suggested the formation of the intramolecular hydrogen bond between the two hydroxyl groups of 1,3-BD above xOS = ∼0.9. To further evaluate the intramolecular hydrogen bonding of 1,3-BD in AN-water binary solvents, molecular dynamics (MD) simulations and NMR experiments for spin-lattice relaxation times T1 and 1H-1H nuclear Overhauser effect (NOE) were conducted on 1,3-BD in the AN system. These results showed the intramolecular hydrogen bond within 1,3-BD in the AN-water binary solvents in the high AN mole fraction range of xAN > 0.9. Especially, the pair correlation functions g(r) of the OH-O interactions of 1,3-BD obtained from the MD simulations indicated that the intramolecular hydrogen bond remarkably increases in the AN solvent as the xAN rises to the unity.

Experimental Measurement and Modeling of Vapor–Liquid Equilibrium for the Ternary System Water + Acetonitrile + Ethylene Glycol

This paper presents vapor–liquid equilibrium (VLE) measurement and correlation for water + acetonitrile + ethylene glycol. Isobaric VLE data were reported for the ternary system at p = 101.3 kPa. The NRTL model was used for the correlation with binary parameters of water + ethylene glycol being fixed as the same for water + ethanol + ethylene glycol in the literature. The correlation showed good agreement with experimental data. Mean absolute deviations were 0.15 K for equilibrium temperature and 0.0025 for vapor-phase mole fraction of acetonitrile, respectively. The reliability of the present correlation was also verified in terms of activity coefficients of water and acetonitrile and relative volatility of acetonitrile to water. With the addition of ethylene glycol, the azeotrope of water + acetonitrile can be removed at a glycol mole fraction of 0.277. Comparisons were presented for correlations available in the literature. Effect of ethylene glycol on water + acetonitrile was compared with that on water + alcohol.

Ab initio study of the structural properties of acetonitrile–water mixtures

Structural properties of acetonitrile and acetonitrile–water mixtures are studied using Density Functional Theory (DFT) and ab initio molecular dynamics simulations. Stable molecular clusters consisted of several water and acetonitrile molecules are identified to provide microscopic understanding of the interaction among water and acetonitrile molecules. Ab initio molecular dynamics simulations are performed to study the liquid structure at the finite temperature. Three mixing compositions in which the mole fraction of acetonitrile equals 0.109, 0.5 and 0.891 are studied. These compositions correspond to three distinct structural regimes. At the 0.109 and 0.891 mole fraction of acetonitrile, the majority species are mostly connected among themselves and the minority species are either isolated or forming small clusters without disrupting the network of the majority species. At the 0.5 mole fraction of acetonitrile, large water and acetonitrile clusters persist throughout the simulation, exhibiting the microheterogeneous behavior in acetonitrile–water mixtures in the mid-range mixing ratio.

Solvation structure of sodium chloride (Na+–Cl−) ion pair in dimethyl sulfoxide–acetonitrile mixtures

Constrained molecular dynamics method has been used to compute the potentials of mean force (PMFs) of Na+-Cl− in dimethyl sulfoxide (DMSO)–acetonitrile (AN) binary mixtures. The PMFs are confirmed by calculating the residence times of the ion pair at various inter-ionic separations. Contact ion pairs (CIPs) are found to be more stable than the solvent shared ion pairs (SShIPs). The stabilities of CIPs generally increase with increase in the mole fraction of AN. The running coordination number analysis shows that the coordination number of Na+ in pure acetonitrile is 4.6, close to the experimental value by FTIR and refractometric study. The preferential solvation study through the excess coordination numbers shows that both Na+ and Cl− are preferentially solvated by DMSO, unlike the water–DMSO mixtures.

Thermodynamic study of complex formation between Ni2+ and Co2+ cations and 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5) in binary mixed nonaqueous solutions

Conductometric titrations were performed in pure and binary solvent solutions of ethyl acetate (EtOAc), methyl acetate (MeOAc) and methanol (MeOH) with acetonitrile (AN) at 288, 298, 308, and 318 K to determine the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of nickel(II) and cobalt(II) cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5). The stability constants of the resulting 1:1 complexes formed between the metal cations and the ligand in different solvent mixtures were determined by computer fitting of the conductance-mole ratio data. The results revealed that the stability order of (kryptofix 5)-Ni2+ and (kryptofix 5)-Co2+ complexes changes with nature and composition of the solvent system. There is a non-linear relationship between the logKf values of complexes and the mole fraction of acetonitrile in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the nickel(II) and cobalt(II) cations with the acyclic ligand changes with the nature of the solvent. The enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, in most of systems, the complexation processes of nickel(II) and cobalt(II) cations with kryptofix 5, are both enthalpy and entropy stabilized and the values of these parameters are influenced by the nature and composition of the binary mixed solvent solutions.

Characterization of the Acetonitrile Aqueous Solution/Vapor Interface by Liquid-Jet X-ray Photoelectron Spectroscopy

We report photoelectron spectroscopy measurements from binary acetonitrile–water solutions, for a wide range of acetonitrile mole fractions (xCH3CN = 0.011–0.90) using a liquid microjet. By detecting the nitrogen and carbon 1s photoelectron signal of CH3CN from aqueous surface and bulk solution, we quantify CH3CN’s larger propensity for the solution surface as compared to bulk solution. Quantification of the strong surface adsorption is through determination of the surface mole fraction as a function of bulk solution, xCH3CN, from which we estimate the adsorption free energy using the Langmuir adsorption isotherm model. We also discuss alternative approaches to determine the CH3CN surface concentration, based on analysis of the relative amount of gas- versus liquid-phase CH3CN, obtained from the respective photoelectron signal intensities. Another approach is based on the core-level binding energy shifts between liquid- and gas-phase CH3CN, which is sensitive to the change in solution surface potential an...

Analysis of the structure of acetonitrile aqueous solutions based on study of their volumetric elastic properties

The evolution of the structure of acetonitrile aqueous solutions is investigated by analyzing the concentration and temperature dependences of density, ultrasound velocity, adiabatic compressibility, excess molar volume, and excess adiabatic compressibility. It is shown that, the region in which solutions exist can be divided into five intervals that differ by solution structure. The structural features are described for each of them. It is found that in the 0.1 ≤ x ≤ 0.9 range of acetonitrile mole fractions, excess adiabatic compressibility isotherms behave abnormally: its absolute value increases with temperature, testifying to the important role played by the CH3 group of the amide residue of acetonitrile in molecular interactions.

Persistence of Acetonitrile Bilayers at the Interface of Acetonitrile/Water Mixtures with Silica

Previous experiments and simulations have shown that acetonitrile organizes into a lipid-like bilayer at the liquid/silica interface. Recent simulations have further suggested that this bilayer structure persists in mixtures of acetonitrile with water, even at low acetonitrile concentrations. This behavior is indicative of microscopic phase separation of these liquids near silica interfaces and may have important ramifications for the use of acetonitrile in chromatography and heterogeneous catalysis. To explore this phenomenon, we have used vibrational sum-frequency-generation spectroscopy to probe acetonitrile/water mixtures at a silica interface. Our spectra provide evidence that acetonitrile partitions to the hydrated silica interface even when the mole fraction of acetonitrile is as low as 10%. A blue shift is observed in the spectrum of the methyl symmetric stretch upon increasing water mole fraction, in agreement with vibrational spectra of bulk mixtures. Line shape analysis suggests that acetonitrile may exist in the form of bilayer patches at high water mole fractions.

Sound velocity measurements in the water + acetonitrile system at temperatures from 293.15 to 323.15 K and its implications on thermodynamic data processing

It has been claimed that partial molar volumes of water + acetonitrile (AN) mixtures show extremes at AN-rich mixtures. Since partial molar volumes are obtained by differentiation of curves fitting experimental data, it was deemed reasonable to check if such a discontinuity exists. With this goal, density and sound velocity have been measured over the whole composition range at 293.15, 298.15, 303.15, 308.15, 313.15, 318.15 and 323.15 K. From these values, isentropic compressibility and intermolecular free lengths, as well as excess quantities for sound velocity, isentropic compressibility and intermolecular free length have been calculated. Density values are in good agreement with previous published values and a minimum in isentropic compressibility appears at around 0.04 mole fraction of AN. This behaviour is not consistent with the claim that inflection points occur in the density curve at high AN content.

Simultaneous Quantification of Carbohydrates, Alcohols, and Toxic Components in a Bio-Based Medium Using Dual-Detection HPLC Analysis

Bio-based media, derived from cellulosic biomass depolymerisation or bioconversion processes, are composed of several chemicals and biochemicals. In this study, the main components of a hemicellulosic-based medium were analyzed using a dual detection HPLC method to separate and determine concentrations of the major monosaccharides (glucose, xylose, and arabinose), alcoholic and acidic components (ethanol, xylitol, and acetic acid) and furanic compounds (furfural and hydroxymethylfurfural (HMF)). The analyses, which employed a single stationary phase (Aminex HPX-87H) and two detection methods, were carried out under isocratic conditions and involved mobile phases consisting of 5 mM sulfuric acid and acetonitrile in different mix ratios from 0 to 0.061 mole fraction of acetonitrile. Based on the analysis run time and the chromatogram quality, the optimum condition was determined for the simultaneous quantification of the components.

A Comparison of Complexation of Li+ Ion with Macrocyclic Ligands 15-Crown-5 and Benzo-derivatives in Binary Nitromethane–Acetonitrile Mixtures by Using Lithium-7 NMR Technique and Ab Initio Calculation

Lithium-7 nuclear magnetic resonance (NMR) measurements were used to investigate the stoichiometry and stability of Li+ complexes with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5) and dibenzo-15-crown-5 (DB15C5) in a number of nitromethane (NM)–acetonitrile (AN) binary mixtures. In all cases, the exchange between the free and complexed lithium ion was fast on the NMR time scale and a single population average resonance was observed. While all crown ethers form 1:1 complexes with Li+ ion in the binary mixtures used, stepwise formation constants of the 1:1 (ligand/metal) complexes were evaluated from computer fitting of the NMR-mole ratio data to equations which relate the observed metal ion chemical shifts to formation constants. There is an inverse linear relationship between the logarithms of the stability constants and the mole fraction of AN in the solvent mixtures. The stability order of the 1:1 complexes was observed to be 15C5.Li+ > B15C5.Li+ > DB15C5.Li+. The optimized structures of the free ligands and their 1:1 complexes with the Li+ ion were predicted by ab initio theoretical calculations using the Gaussian 98 software. The results of calculations are discussed. .

A comparison of complexation of Li + ion with macrocyclic ligands 15-crown-5 and 12-crown-4 in binary nitromethane–acetonitrile mixtures by using lithium-7 NMR technique and ab initio calculation

Lithium-7 NMR measurements were used to investigate the stoichiometry and stability of Li + complexes with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), dibenzo-15-crown-5 (DB15C5) and 12-crown-4 (12C4) in a number of nitromethane (NM)–acetonitrile (AN) binary mixtures. In all cases, the exchange between the free and complexed lithium ion was fast on the NMR time scale and a single population average resonance was observed. While all crown ethers form 1:1 complexes with Li + ion in the binary mixtures used, both 1:1 and 2:1 (sandwich) complexes were observed between lithium ion and 12C4 in pure nitromethane solution. Stepwise formation constants of the 1:1 and 2:1 (ligand/metal) complexes were evaluated from computer fitting of the NMR-mole ratio data to equations which relate the observed metal ion chemical shifts to formation constants. There is an inverse linear relationship between the logarithms of the stability constants and the mole fraction of acetonitrile in the solvent mixtures. The stability order of the 1:1 complexes was found to be 15C5·Li + > B15C5·Li + > DB15C5·Li + > 12C4·Li +. The optimized structures of the free ligands and their 1:1 and 2:1 complexes with Li + ion were predicted by ab initio theoretical calculations using the Gaussian 98 software, and the results are discussed.

Nuclear magnetic resonance study of the stoichiometry and stability of lithium ion complexes with two small size crown ethers in binary nitromethane–acetonitrile mixtures

Lithium-7 NMR spectrometry was used to study the complexation reaction between lithium ions and different small size crown ethers12-crown-4 (12C4), benzo-12-crown-4 (B12C4) in a number of binary nitromethane (NM)–acetonitrile (AN) mixtures. The exchange between the free and complexed lithium ion was fast on the NMR time scale and a single population average resonance was observed. Both 1:1 and 2:1 (sandwich) complexes were observed between lithium ion and 12C4 and B12C4 in pure nitromethane solution. Stepwise formation constants of the 1:1 and 2:1 (ligand/metal) complexes were evaluated from computer fitting of the NMR-mole ratio data to equations which relate the observed metal ion chemical shifts to formation constants. There is an inverse linear relationship between the logarithms of the stability constants and the mole fraction of acetonitrile in the solvent mixtures. The stability order of the 1:1 and 2:1 complexes was found to be 12C4.Li+ > B12C4.Li+. The optimized structures of the free ligands and their 1:1 and 2:1 complexes with Li+ ion were predicted by ab initio theoretical calculations using the Gausian 98 software, and the results are discussed. Stoichiometry and stability of the Li+ complexes with12-Crown-4 and Benzo-12-crown-4 were investigated by 7Li NMR in nitromethane-acetonitrile mixtures. The optimized structures of the free crowns and their 1:1 and 2:1 complexes with Li+ ion were predicted by ab initio theoretical calculations using the Gausian 98 software.

Determination of Dissociation Constants of Folinic Acid (Leucovorin), 5-Fluorouracil, and Irinotecan in Hydro-organic Media by a Spectrophotometric Method

In this study, a multiwavelength spectrophotometric method was used for the determination of the dissociation constants of drugs used for treatment of colorectal cancer, folinic acid (leucovorin), 5-fluorouracil, and irinotecan, in water and acetonitrile−water binary mixtures up to a 0.50 volume fraction at 25 °C and an ionic strength of 0.1 mol·L−1 KCl. The absorbance/pH profiles were assessed and found to conform to those of polyprotic acids. Data evaluation was performed using the STAR software program which calculates stability constants and molar absorbances of the pure species by multilinear regression. A linear relationship between acidity constants and the mole fraction of acetonitrile in the solvent mixture was observed. The effect of solvent properties on acid−base behavior is discussed.