Determination of stability constants of copper(II) complex of glycine in water + alcohol mixed solvents with ion selective electrode technique

The first stability constants (log beta(1)) of the copper(II) complex of glycine in water and in 13 water + alcohol (isopropanol, tert-butanol, 1,2-propylene glycol and glycerol) solvents have been determined at 25 degrees C and an ionic strength of 0.10, from pH and pCu measurements of cells containing copper(II) ion selective electrode. It has been shown that as the proportion of the alcohol increases, the stability constants become increasing positive in all of the mixed solvents examined. An almost linear relation between log beta(1) and the mole fraction of alcohol was found for the complex in aqueous solutions of isopropanol, tert-butanol and glycerol. The response of the copper(II) ion selective electrode in water and in water + alcohol mixed solvents was also investigated. The advantages of using an ion selective electrode to determine the stability constants in mixed solvents are discussed.     

Potentiometric determination of the dissociation constants of L-histidine, proline and tryptophane in various hydroorganic media

The dissociation constant values of L-histidine, proline and tryptophane were determined at 25 +/- 0.1 degrees C by potentiometric pH titration in pure water and different hydroorganic solvent media. The organic solvents used were methanol, ethanol, N,N-dimethylformamide, dimethyl sulfoxide, acetone and dioxane. Initial estimates of the dissociation constant values of the different amino acids studied have been refined with ESAP2M computer program. It was observed that changing the medium permittivity as the solvent is enriched in methanol or ethanol has little influence on the pK*(a) values of the amino acids studied. The results obtained are discussed in terms of average macroscopic properties of the mixed solvents and the possible variation in microheterogeneity of the salvation shells around the solute.     

Solvent effects on the rate of the keto-enol interconversion of 2-nitrocyclohexanone

The rates of tautomerization of 2-nitrocyclohexanone (2-NCH) have been measured spectrophotometrically at 25.0 +/- 0.1 degrees C in several organic aprotic solvents and their binary mixtures. In cyclohexane the reaction is effectively catalyzed by bases and inhibited by acids while the so-called "spontaneous reaction" appears essentially due to autocatalysis. Apparent second order rate constants (k(app)(B)) for the reaction catalyzed by triethylamine (TEA) and pyridine (Pyr) have been obtained. From the experimental k(app)(B) values rate constants for the enolization (k(1)(B)) and ketonization (k(-1)(B)) reactions have been calculated. A Kamlet-Taft type linear solvation energy relationship (LSER) adequately accounts for the observed solvent effects. Activation parameters for both reactions show that solvent effects are mainly entropic in origin and that there is a shift of the transition state from a ketone-like to an enol-like structure on passing from less to more polar solvents.     

Thermodynamic study of the second-stage dissociation of N,N-bis-(2-hydroxyethyl)glycine (bicine) in water at different ionic strength and different solvent mixtures

The second stage dissociation constant pK2 of N,N-bis-(2-hydroxyethyl)glycine (bicine) has been determined in aqueous solution at different ionic strengths and different temperatures, using pH-metric technique. The thermodynamic quantities (deltaG(o), deltaH(o), and deltaS(o)) have been studied and discussed. Evaluation of the effect of organic solvent of the medium on the dissociation processes have also been reported and discussed. The organic solvents used were methanol, dimethylsulfoxide (DMSO), and dioxane. The pK2 for the ionization in water +10, +20, +30, +40, and +50 wt % dioxane has been determined at five different temperatures from 15 to 35 degrees C at intervals of 5 degrees C. The thermodynamic quantities were calculated. The implications of the results with regard to specific solute-solvent interactions (particularly stabilization of zwitterionic species) are also discussed.     

Spectrophotometric determination of the dissociation constants of methyl yellow in mixed protic solvents

The concentration dissociation constants (pK(a)) of methyl yellow, MY (H(+)In) in mixed aqueous solvents of methanol, ethanol, iso-propanol, tert-butanol have been accurately determined from spectrophotometric measurements at 25 degrees C and a constant ionic strength of 0.1 mol l(-1). It has been shown that in these solvents, the pK(a) values decrease with increasing composition of the organic co-solvent. A linear relationship between pK(a) and the mole fraction (x(2)) of the co-solvent was observed in a limited range of the compositions for each of the solvent systems. The results have been discussed in the light of transfer thermodynamic properties of the species existing in the dissociation equilibrium, solvent basicity and solute-solvent interactions. Furthermore, it was also observed that with the change of the solvents, the absorption spectra of MY shifted apparently and the color transition changed accordingly. The solvent effect on the spectra has been attributed to the isomerization equilibria of MY. A simple application of MY was also shown to the sodium acetate-hydrochloric acid titrations in the mixed solvents.     

Utility of 1-octanol/octane mixed solvents for the solvent extraction of aluminum(III), gallium(III), and indium(III) with 8-quinolinol.

Using 1-octanol/octane mixed solvents, the extraction of aluminum(III), gallium(III) and indium(III) with 8-quinolinol was carried out at 25 degrees C. The formation constants of the respective metal(III) 8-quinolinolates in the aqueous phase and their partition constants between the mixed solvents and water were determined based on an analysis of the extraction equilibria. The relationship between the partition constants of 8-quinolinol and its complexes was analyzed by the regular solution theory. The molar volumes of aluminum(III), gallium(III) and indium(III) 8-quinolinolates, calculated from the present results, suggest that the electrostriction effect functions in complex forming. It has been found that octane/1-octanol mixed solvents were available not only for the extraction of metal ions, but also for determining the formation constants of these metal 8-quinolinolates in the aqueous phase and their partition constants.     

Gas—liquid equilibrium in hydrogen + tetralin + diphenylmethane and hydrogen + tetralin + m-xylene

Vapor—liquid equilibrium data in two ternary mixture systems, hydrogen + tetralin + diphenylmethane and hydrogen + tetralin + m-xylene, were determined in a flow apparatus at pressures 20–250 atm¹ for both systems, and temperatures 190–430°C for the first system and 190–310°C for the second. Mixed solvents approximately equi-molal in the organic compounds were studied. Henry constants of hydrogen in the mixed solvents were evaluated from the data. The results show that the solubility of hydrogen in these mixed hydrocarbon solvents can be completely predicted from solubilities in the pure component liquids.     

Spectroscopic study of association of a hemicyanine dye in mixed aqueous binary solvents

Electronic absorption and steady state emission properties of a hemicyanine dye [4-[4-(dimethylamino)styryl]-1-docosylpyridinium bromide], have been studied in several pure solvents and two mixed binary solvents (water+ethanol and water+acetonitrile). In pure solvents the band-width of the absorption spectrum correlates well with the Stoke's shift. In mixed aqueous solvents two different molecular forms of the solute, viz. the monomer and the dimer of the solute exists in equilibrium. Thermodynamic parameters (e.g. the Delta G degrees and Delta H degrees ) characterizing the equilibrium have been determined. While the value of Delta G degrees changes very slightly with the composition of the binary mixture, the value of Delta H degrees has been observed to depend significantly with solvent composition.     

Electrochemical and thermodynamic studies of the ion-pair formation of chloropentamminecobalt(III) ion in ethyl alcohol-water media containing different dicarboxylate ligands

The ion-pair dissociation constants, K(D), of the ion-pair formed between chloropentamminecobalt(III) ion (CpX(2+)) and a variety of dicarboxylate ligands, have been determined from EMF measurements of a cell composed of glass and calomel electrodes. Measurements were made in water and in aqueous binary mixtures of ethyl alcohol, over a wide range of solvent composition (0-60 wt% ethyl alcohol), at six different temperatures (ranging from 30 to 55 degrees C at intervals of 5 degrees C). The thermodynamic parameters of association DeltaG(ass)(0), DeltaH(ass)(0) and DeltaS(ass)(0) have been calculated and discussed. DeltaH(ass)(0)-DeltaS(ass)(0), DeltaS(ass)(0)-DeltaS(1(or 2))(0), DeltaG(ass)(0)-G(1(or 2))(0) and DeltaH(ass)(0)-DeltaH(1(or 2))(0) correlations among different solvent media and different dicarboxylate ligands were examined (where 1 and 2 denote the first and the second dissociation reactions of the studied dicarboxylic acids). The pK(D) value has been correlated with the dielectric constant of the medium according to Born's equation.     

Effects of solvation on partition and dimerization of benzoic acid in mixed solvent systems

The partition of benzoic acid between 0.1M perchloric acid solution and two kinds of mixed solvents has been carried out at 25 degrees C. The partition and dimerization constants of benzoic acid have been determined in the 1-octanol-benzene and 2-octanone-benzene systems. In both the mixed solvent systems, with increasing content of 1-octanol and 2-octanone in each mixed solvent, the partition constant of benzoic acid has been found to increase, and the dimerization constant of benzoic acid in each organic phase to decrease. These phenomena are attributable to solvation of monomeric benzoic acid by 1-octanol and 2-octanone molecules in each mixed solvent.     

Recovery of some common solvents from protective clothing breakthrough indicator pads by microwave-solvent extraction and gas chromatography

The efficiency of solvent adsorption using Permea-Tec general solvent pads, used for the detection of chemical breakthrough of protective clothing, was determined for methanol, acetone, ethyl methyl ketone, trichloroethylene (TriCE), tetrachloroethylene (TetCE), toluene, m-xylene, and D-limonene. Known volumes of single or mixed solvents were added to pads in the range 0.2-5.0 microliters (0.16-8.13 micrograms). After microwave-solvent extraction (ME) into hexan-1-ol, the samples (0.5-3.0 microliters) of the filtered and extracted solutions were analyzed by gas chromatography. All solvents exhibited > 97% adsorption on the pads at spiking levels of 0.48-0.98 microgram for each solvent. The solvent recovery for the system was calculated for each solvent, with solvents with boiling points below 110 degrees C showing recoveries of > 90%, and with solvents with boiling points above 110 degrees C showing recoveries from 80 to 90%. The recovery precision was good (RSD < or = 4%) for all solvents over the range 1.0-2.5 microliters of applied solvents to pads for ME and 1.0 microliter of extracted solutions for GC analysis.     

Solution behavior of metal sulfonate ionomers. II. Effects of solvents

Previous studies on the dilute-solution behavior of sulfonated ionomers have shown these polymers to exhibit unusual viscosity behavior in mixed solvents of low polarity. These results have been interpreted as arising from specific solvation effects by the solvents with the metal sulfonate groups which persist as ion pairs. The consequences of ion pair interactions and their solvation are exceptional thickening behavior at low polymer levels as compared to unfunctionalized polymers, and anomolous solution viscosities with varying temperature. These studies have now been extended to single-component solvents which traverse a range of polarities. Using the sodium salt of lightly sulfonated polystyrene (S-PS) as a model system, the authors found the solution behavior in low-polarity solvents (tetrahydrofuran) to be consistent with that observed previously for mixed solvents; ion pair interactions predominated. However, in polar solvents such as dimethyl sulfoxide or dimethyl formamide, these polymers behave as classic polyelectrolytes even at sulfonate levels below 2 mol %. The behavior of the S-PS acids is similar to that observed for the metal salts. To a first approximation these two behaviors, ion pair association and polyelectrolyte behavior, are dependent on solvent polarity. In some cases it is possible to induce polyelectrolyte behavior in a S-PS/solvent combination exhibiting ion pair interactions by the addition of very low levels of a polar cosolvent, such as water. These results again demonstrate the selectivity of the solvent-sulfonate interactions.     

Thermodynamics of the distribution of some carboxylic acids between organic solvents and a perchlorate solution.

The distribution of formic, benzoic and 4-methylbenzoic acids between a 0.1 mol dm(-3) (Na+, H+)ClO4- solution and octanol and carbon tetrachloride was studied at five different temperatures of 10 - 30 degrees C. The thermodynamic parameters for the transfer process of monomeric acid between two phases and for the dimerization of monomeric acid in carbon tetrachloride (deltaH and deltaS) were evaluated from the van't Hoff isochore. The free-energy change for the transfer of a methylene group from water to organic solvents was entropically controlled, irrespective of the organic solvents. The distribution constants of formic and benzoic acids were larger than those expected from the distribution constants of acetic and phenylacetic acids, respectively. The free-energy change for all solutes, except for benzoic and 4-methylbenzoic acids, was also entirely entropically controlled in the case of octanol as a solvent. The enthaly-entropy compensation for the dimerization constant of acids in carbon tetrachloride was observed.     

Practical and efficient Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by recyclable Pd(0)/C

The first Suzuki-Miyaura cross-coupling of 2-iodocycloenones with arylboronic acids catalyzed by 10% Pd(0)/C is described as an interesting alternative to classical homogeneous conditions. Most of the substrate reacted under mild condition at 25 degrees C under air in aqueous DME. The conditions described tolerate a wide range of iodoenones and boronic acids. Notably, the procedure features inexpensive reagents and solvents with low toxicity rendering the method environmentally benign. Additionally 10% Pd(0)/C could be recovered and efficiently reused at least five times without significant alteration of the yields of the cross-coupled product.     

Thermodynamic dissociation constants of N-phenylbenzohydroxamic acids and benzohydroxamic acid

Thermodynamic association constants of benzohydroxamic acid and several ortho-substituted N-phenylbenzohydroxamic acids have been determined by pH titration in aqueous dioxan media at 25 degrees and 35 degrees . Empirical pH corrections for mixed aqueous media have been applied. The pK(a) values do not vary linearly with the reciprocal of dielectric constant of the medium, but a plot of pK(a) vs. the mole fraction of dioxan is linear at a given temperature. Values of DeltaG degrees , DeltaH degrees and DeltaS degrees are tabulated.     

The acidity constants of some pyrimidine bases in various water-organic solvent media

The acid ionization constants of some pyrimidine bases of nucleic acids were determined pH-metrically at 25 degrees C and at the constant ionic strength I = 0.10 mol l(-1) (KNO3) in pure water as well as in aqueous media containing variable mole percentages (5-30%) of organic solvents. The organic solvents used were methanol, ethanol, N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), acetonitrile, acetone and dioxane. The results obtained indicated that the acidity constants are generally decreased as the content of an organic solvent in the medium is increased. It was deduced that the hydrogen bonding interactions and the solvent basicity in addition to the electrostatic effect are the major effects influencing significantly the acid ionization process of pyrimidine bases in the different water-organic solvent media. Some thermodynamic parameters (deltaH, deltaG degrees, deltaS degrees) of the ionization process over the temperature range 5-45 degrees C in pure water were also determined and discussed.     

Fiber-optic infrared spectroelectrochemical studies of six-coordinate manganese nitrosyl porphyrins in nonaqueous media

The redox behavior of the six-coordinate (por)Mn(NO)(1-MeIm) (por = tetraphenylporphyrin dianion (TPP), tetratolylporphyrin dianion (TTP), or tetra-p-methoxyphenylporphyrin dianion (T(p-OMe)PP)) complexes were examined by cyclic voltammetry at room temperature and at -78 degrees C in two nonaqueous solvents (CH2Cl2 and THF) at a Pt disk electrode. In CH2Cl2 at room temperature, the compounds undergo four oxidations and two reductions within the solvent limit; in THF, the compounds undergo one oxidation and three reductions. In both solvents, the first oxidation represents a chemically irreversible one-electron process involving the rapid loss of nitric oxide. The oxidation occurs at the MnNO site as judged from bulk electrolysis, UV-vis spectroscopy at room temperature, and IR spectroelectrochemistry at room temperature and at -78 degrees C. The second oxidation, accessible in CH2Cl2, is also chemically irreversible and occurs at the porphyrin ring; the third and the fourth oxidations are, on the other hand, chemically reversible but also occur at the porphyrin ring. The first reduction is chemically irreversible in CH2Cl2, occurs at the porphyrin ring, and is followed by loss of NO. In THF, the first reduction is chemically reversible and is followed by reversible loss of NO.     

甲烷在水-叔丁醇混合溶剂中的溶解度

在303.15 K、313.15 K、323.15 K、333.15 K温度下，0－6 MPa压力范围内测定了甲烷在水－叔丁醇混合溶剂中的溶解度．溶剂中叔丁醇的摩尔分数(x_(TBA))从0到1．结果表明，在温度和溶剂组成一定条件下，甲烷的溶解度随其分区的增加而增大，随x_(TBA)的增加，在富水区内，甲烷的溶解度变化较缓慢，当x_(TBA)超过某值时，甲烷的溶解度随x_(TBA)的增加而增大，并且幅度较大；在x_(TBA)约为0－0.045范围内，甲烷的溶解度随温度增加而减小，x_(TBA)约在0.045－0.15范围内，溶解度随温度增加而增加，x_(TBA)约在0.15～1.0范围内，溶解度随温度增加而减小．根据溶解度与温度和溶剂组成的关系可以推测，在303.15－333.15 K、0－6 MPa范围内，水－叙丁醇混合溶剂中仍存在笼合物结构．根据溶解度与温度、压力的关系讨论了甲烷在此混合溶剂中的亨利常数、偏摩尔体积、标准溶解自由能、标准溶解焓和标准溶解熵．     

Multidimensional liquid chromatography system with an innovative solvent evaporation interface

An orthogonal two-dimensional liquid chromatographic (2D-LC) system was developed by using a vacuum-evaporation loop-type valve interface. Normal-phase liquid chromatography (NPLC) with a bonded CN phase column was used as the first dimension, and reversed-phase liquid chromatography (RPLC) with a C(18) column was used as the second dimension. All the solvents in the loop of the interface were evaporated at 90 degrees C under vacuum conditions, leaving the analytes on the inner wall of the loop. The mobile phase of the second dimension dissolved the analytes in the loop and injected them onto the secondary column, allowing an on-line solvent exchange of a selected fraction from the first dimension to the second dimension. The chromatographic resolution of analytes on the two dimensions was maintained at their optimal condition. Sample loss due to evaporation in the interface was observed that depended on the boiling point of the compound. Separation of sixteen polycyclic aromatic hydrocarbon mixtures and a traditional Chinese medicine Angelica dahurica was demonstrated.     

Thermodynamic Parameters of the Dissolution of 4-Hydroxy-L-Proline and L-Phenylalanine in Mixed Aqueous Solvents at 298 K

The enthalpies of solution of 4-hydroxy-L-proline and L-phenylalanine in binary mixed aqueous solvents containing acetonitrile (AN), 1,4-dioxane (1,4-DO), or acetone (AC) at mole fractions of 0 to 0.25 are determined at T = 298.15 K via isothermal calorimetry. The standard enthalpies of solution (Δ_solH°) and transfer (Δ_trH°) of 4-hydroxy-L-proline and L-phenylalanine from water to mixed aqueous solvents are calculated using the experimental calorimetric data, as are the enthalpy coefficients of paired interactions (h _xy ) between the molecules of the investigated amino acids and the organic solvents. The effects the mixed aqueous solvent composition and the structure of the organic solvent molecules have on the enthalpies of solution and transfer for the investigated amino acids are considered. The correlation between the enthalpy of solution of the amino acids and the electron-donating properties of the organic solvents in the mixed aqueous solvent systems is established.