Conductance of Dilute Sodium Acetate Solutions to 469 K and of Acetic Acid and Sodium Acetate/Acetic Acid Mixtures to 548 K and 20 MPa

In order to obtain accurate association constants for sodium acetate, a very precise flow method was used to measure the electrical conductivity of dilute aqueous solutions of sodium acetate at ambient conditions and 469 K and 20 MPa. Measurements at ambient conditions, 469 and 548 K and 20 MPa, were also made on sodium acetate/acetic acid mixtures and acetic acid. In order to determine the limiting the equivalent conductances and the association constant for sodium acetate, and dissociation constant for acetic acid, the results were fitted to two modern conductance equations (Fuoss–Hsia–Fernandez–Prini and Turq–Blum–Bernard–Kunz) with accompanying activity coefficient models (mean spherical approximation and the Debye–Hückel with the Bjerrum distance). The choice of conductance equation, activity coefficient model, assumed values for the limiting equivalent conductance for minor species, and assumed equilibrium constants for minor reactions, did not significantly change the resulting equilibrium constants. The insensitivity of the calculated equilibrium constants to these choices in conjunction with the inherent precision of the flow conductance technique leads us to believe that the present results are the most accurate sodium acetate ion-pairing constants published to date. Our results for acetic acid are in good agreement with previously published results from other laboratories.     

Étude d'équilibres en solution à l'aide des échangeurs d'ions: II Détermination des constantes de dissociation des perchlorates alcalins dans les mélanges eau—acide acétique—acide perchlorique

The thermodynamic dissociation constants of lithium, sodium, potassium, rubidium and cesium perchlorates in water—acetic acid—perchloric acid mixtures have been determined by an ion-exchange method. The distribution coefficients of alkaline elements have been measured in water—acetic acid—perchloric acid mixtures containing a variable quantity of water (4–100 % by weight) and a constant amount of perchloric acid. The variation of these distribution coefficients with perchloric acid concentration has been studied in various mixtures containing a constant amount of water (less than 20 % $\text{w}\text{w}$). The results have been used to determine the dissociation constants of alkaline perchlorates and the selectivity coefficients of alkaline ions and hydrogen ion in the aqueous organic mixtures studied.     

Ion Association Between Hexaamminecobalt (III) Ion and Monovalent Anions in Methanol-Water Mixtures from 10 to 50°C

The conductivities of chloride, bromide, iodide, nitrate, and perchlorate of hexaamminecobalt(III) complex were measured in 10-80 wt.% methanol-water mixtures at varying temperatures from 10 to 50°C. The ion association constants were estimated by analyzing conductivity data in terms of the Robinson-Stokes equations. Ion-association constants calculated for all complex salts in methanol-water mixtures increased, depending on the percentage of methanol. This was equivalent to the ion-association constants increasing with a decrease in the the dielectric constant of the mixtures. K _A values increased with increasing temperature for the chloride, bromide, and iodide of [Co(NH₃)₆]³⁺. It was observed that these values indicated some disorder, dependent on the temperature, for nitrate and perchlorate. Thermodynamic parameters (Gibbs' free energy, entropy and enthalpy of ion association) were estimated from the temperature dependence of the ion-association constant. The limiting molar conductivities of complex ion and monovalent anions in the mixed solvents were determined from our experimental data by using the Kohlraush equation.     

Complexes between disubstituted benzo-15-crown-5 ligands and sodium or potassium bromides

Stability constants have been determined with ion selective electrodes for complexes between sodium or potassium bromide in methanol with each of four crown ethers, benzo-15-crown-5 (Ia), dibromobenzo-15-crown-5 (Ib), dimethoxybenzo-15-crown-5 (Ic) and di-n-butoxybenzo-15-crown-5 (Id). Those for (Ib) were significantly lower than the others. The stability constants for complexes between sodium bromide and (Ia) and (Ib) in dimethylformamide (DMF) were found to be about one fifth of the corresponding values in methanol. The conductivity method was used to measure the ion pairing in methanol of sodium bromide alone and in the presence of (Ia), (Ib), or (Ic). Ion pairing is increased on complexation, the association constants being 3.3 mol^–1 dm³ for Na⁺ Br^– and 20–23 mol^–1 dm³ for Na(Ia–c)⁺ Br^–. The syntheses of compounds (Ic) and (Id) are described.     

Anomalies in the twist elastic behaviour of mixtures of calamitic and bent-core liquid crystals

ABSTRACT

The splay, twist and bend elastic constants (K₁₁, K₂₂ and K₃₃) have been measured as a function of temperature in bent-core/calamitic mixtures based on three different calamitic materials (5CB, 8CB and ZLI1132) and two bent-core dopants. The behaviour of the splay and bend constants are as expected; a reduction in K₃₃ of ~20%, in line with predictions from mixing rules and other observations. Interestingly, no change is seen in the splay constant, K₁₁ of the calamitic hosts. Surprisingly though, the twist elastic constant exhibits a reduction of 30 – 40% in all mixtures across the nematic range, an effect not previously reported and much larger than mixing rules can explain. The elastic behaviour is universal in our mixtures. We explain part of the reduction in the twist deformation by considering the influence of the chiral conformer fluctuations of the bent-core molecules on the twist elastic constants of the mixtures. However, the dramatic reduction can only be fully explained by also including contributions from chiral conformer fluctuations of the calamitic host, a form of chiral amplification.     

Solute-Solvent Interaction Effects on Protonation Equilibrium of Substituted N-Benzylidene-2-hydroxyanilines in Aqueous Ethanol: The Application of Factor Analysis to Solvatochromic Parameters and Protonation Equilibria

In this study, the stoichiometric protonation constants, logK_OH and logK_NH, of sixteen substituted N-benzylidene-2-hydroxyanilines have been determined potentiometrically in ethanol-water mixtures of varying composition (10–80% ethanol by volume) at 25.0±0.1°C. The values of the constants, logK, were submitted to factor analysis in order to obtain the number of factors which affect the variation of the whole data sets of protonation constants and, afterwards, to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between Schiff bases derivatives and the solvent studied was identified and quantified. Kamlet and Taft general equations allow calculation of the logK values of Schiff bases studied in any ethanol-water mixtures up to 80% (v/v) and thus provide the knowledge of the acid-base behaviour in these solvent media. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol-water mixtures.     

Solute-Solvent Interaction Effects on Protonation Equilibrium of Substituted N-Benzylidene-2-hydroxyanilines in Aqueous Ethanol: The Application of Factor Analysis to Solvatochromic Parameters and Protonation Equilibria

Summary. In this study, the stoichiometric protonation constants, logK_OH and logK_NH, of sixteen substituted N-benzylidene-2-hydroxyanilines have been determined potentiometrically in ethanol-water mixtures of varying composition (10–80% ethanol by volume) at 25.0±0.1°C. The values of the constants, logK, were submitted to factor analysis in order to obtain the number of factors which affect the variation of the whole data sets of protonation constants and, afterwards, to target factor analysis to identify these factors. The influence of solvatochromic parameters in the interactions between Schiff bases derivatives and the solvent studied was identified and quantified. Kamlet and Taft general equations allow calculation of the logK values of Schiff bases studied in any ethanol-water mixtures up to 80% (v/v) and thus provide the knowledge of the acid-base behaviour in these solvent media. Further, the quasi-lattice quasi-chemical (QLQC) theory of preferential solvation has been applied to quantify the preferential solvation by water of electrolytes in ethanol-water mixtures.     

Lanthanum Trifluoromethane-sulfonate‐Catalyzed Facile Synthesis of Per‐O‐acetylated Sugars and Their One‐Pot Conversion to S‐Aryl and O‐Alkyl/Aryl Glycosides†

Lanthanum trifluoromethanesulfonate‐catalyzed solvent‐free per‐O‐acetylation with stoichiometric acetic anhydride proceeds in high yield (95%–99%) to afford exclusively pyranose products as anomeric mixtures. Subsequent anomeric substitution employing borontrifluoride etherate and thiols or alcohols furnished the corresponding 1,2‐trans‐linked thioglycosides and O‐glycosides, respectively, in good to excellent overall yield (75%–85%). Alternatively, reaction of free sugars in neat alcohol employing the same catalyst at elevated temperature gives the corresponding 1,2‐cis‐linked O‐glycosides (along with 1,2‐trans‐linked glycosides as minor product) in good yield (73%–80%). Anomeric mixtures of compounds thus produced were characterized as their per‐O‐acetylated derivatives.      

Influence of the Structure of Steroid Hormones on Their Association with Cyclodextrins: A High-Performance Liquid Chromatography Study

The association constants of fourteen steroid hormones with - and -cyclodextrin were measured in methanol-water (20 : 80 v/v) at 35 °C using the chromatographic Hummel-Dreyer method. It was found that the greatest influence on the association constants is the structural features of ring A of these compounds but the substituents of ring D also alter the complex stability to an appreciable degree. The measured association constants were considerably greater than the corresponding values measured previously in the medium containing more methanol (45 instead of 20%).     

Polarographic Studies of the Reduction of Sn(II) in Dimethylsulphoxide and its Mixtures with Water and Acetonitrile

Abstract

The polarographic reduction of Sn(II) in DMSO, H₂O-DMSO and AN-DMSO mixtures was characterized as being reversible. When the reduction was carried out in an the process was found to be irreversible and in this case the kinetic parameters were determined by Meites and Israel's method. the effect of DMSO on the reduction of Sn(II) in an shows that the Sn(II) forms six successive complexes with DMSO, whose stability constants were determined by Deford and Hume's method.

The Walden product was determined for the mixtures under study. In AN-DMSO it decreases up to 20 vol.% DMSO, and from there remains approximately constant. In the H₂O-DMSO mixtures the Walden product passes through a broad minimum between 60 and 70 vol.% DMSO. the free energy of transfer in the hydro-organic mixture changes gradually with the increase in DMSO content, whereas in the AN-DMSO mixture this energy increases rapidly in very low DMSO content mixtures.     

A Magnesium-Selective Ionophore Containing Four Amide Carbonyl Ligands Derived from L-Tartaric Acid and Axial Furano Oxygen Binding Sites

Octahedrally converging hexadentate macrocyclic receptors 1 and 2, based on L-tartaric acid and furanmoieties, were synthesized andtheir complexation properties studied. In this paper,magnesium ion selectivitiesdetermined by ISE experiments, chiroptical changes observedby circular dichroism(CD) on complexation, and association constants measuredby NMR titration arediscussed.     

Differential Kinetic Determination of Ketone Mixtures

Abstract

A method for the determination of binary ketone mixtures is described which is based on the differential reaction rates of ketones in a large excess of hydroxylamine hydrochloride. The reactions are followed with a pH stat. For mixtures containing ca. 10^?5 moles of ketone, a relative error and precision of 1% was obtained if the rate constants differed by a factor of 5, and 3% if the rate constants differed by 3.     

High Yield Synthesis and Preliminary Spectroscopic Study of Mono-N-alkylated Cyclen Derivatives of Salicylic Acid

Selective and high yield synthesis of N-substituted salicylic acid derivatives of cyclen has been achieved by using a direct synthetic procedure under mild reaction conditions. The protonation constants of these compounds were determined by potentiometric titration. The complexing properties of the cyclen derivatives with metal cations were investigated by UV–Vis spectroscopy and ¹H NMR. The stability constants of Mg²⁺, Ca²⁺ and Sr²⁺ complexes with ligands 5 and 6 were determined.     

The Synthesis,Characterization and Conductance Studies of New Cu(II), Ni(Ii) And Zn(II) Complexes with the Schiff Base Derived from 1,2-Bis-(o-Aminophenoxy)Ethane and Salicylaldehyde

Cu(II), Ni(II) and Zn(II) complexes with the Schiff base derived from 1,2-bis-(o-aminophenoxy)ethane with salicylaldehyde have been prepared. The complexes have been characterized by elemental analysis, magnetic measurements, ¹H NMR, ¹³C NMR, UV, visible and IR spectra as well as conductance measurements. The ligand is coordinated to the central metal as a tetradentate ONNO ligand. The four bonding sites are the central azomethine nitrogen and aldehydic OH groups. The ligand was used for complexation studies. Stability constants were measured by a conductometric method. Furthermore, the stability constants for complexation between ZnCl₂ and Cu(NO₃)₂ salts and N,N′-bis(salicylidene)-1,2-bis-(o-aminophenoxy)ethane (H₂L) in 80% dioxane/water and pure methanol were determined from conductance measurements. The magnitudes of these ion association constants are related to the nature of the solvation of the cation and the complexed cation. The mobilities of the complexes are also dependent, in part, upon solvation effects.     

Solvent effects on the dissociation of aliphatic carboxylic acids in water—N,N-dimethylformamide mixtures

The autoprotolysis constants of several water-_N,N-dimethylformamide mixtures were determined. The acid dissociation constants of formic, acetic, propionic, n-butyric, isobutyric, n-valeric, isovaleric, 2-methylbutyric and trimethylacetic acids were evaluated in the same media by potentiometric titration. Empirical equations for the calculation of autoprotolysis constants and acid dissociation constants at 25° C in the mixed solvents are proposed. Approximate solvation numbers were obtained by multiple linear regression analyses of pK_a values.     

Étude d'équilibres en solution à l'aide des échangeurs d'ions : I Dissociation du perchlorate d'argent et de l'acide nitrique dans les mélanges eau—acide acétique—acide perchlorique ou acide nitrique

A theoretical relationship postulated between the distribution coefficient of a monovalent element and the parameters upon which it depends (acid concentration in solution, dissociation constants of the acid and the salt, selectivity coefficient of exchanged ions) has been verified for the dissociation of silver perchlorate in water—acetic acid—perchloric acid mixtures. The dissociation constants found have been compared with the experimental values obtained by potentiometric measurements. The relationship established has been employed for the determination of nitric acid dissociation constants in water—acetic acid-nitric acid mixtures containing less than 25 % by weight of water. From the results the pK value for nitric acid in pure acetic acid has been evaluated by extrapolation. The theoretical relationship might be used to determine an acid dissociation constant when the dissociation constant of a salt is known and vice versa.     

Potentiometric Measurements in Non-Aqueous Media Using Bromide and Iodide Ion Selective Membrane Electrodes

Abstract

Solid membrane bromide and iodide ion selective membrane electrodes were evaluated for their performance in non-aqueous media. The electrodes were evaluated in several alcohols and glacial acetic acid.     

Kinetic Studies of the Addition of Formaldehyde to Carbamates

Abstract

The rate of formation and dissociation of alkyl N-methylol-carbamates in basic media were studied by electrochemical techniques. The effects of the presence of various N-substituents on these rate constants and equilibrium constants -were investigated. The reactions were carried out at 20. 4°C and pH 12. 45 in water and in a 66% water and 34% t-butanol (v/v) solvent. The rate constants were higher when water was used as the solvent.     

Regioselective Synthesis of α‐Iodoacetates from Alkenes/Ammonium Acetate/I2 by Woodward's Reaction

Abstract

Regioselective synthesis of α‐iodoacetates from alkenes, ammonium acetate, and iodine in acetic acid is reported. The reaction is facile, fast, environmentally, friendly, and cost effective. α‐Iodoacetates are obtained from both acyclic and cyclic alkenes in high yields ranging from 80–95% within 10–20 min.     

Dielectric properties of two high birefringence liquid crystal mixtures in the Sub-THz band

ABSTRACT

In order to produce liquid crystal (LC) with high birefringence (Δn) in the THz band, eight LC monomers were designed and synthesized. We formulate two mixtures (LC S200-2 and E7-2) by adding eight LC monomers to two commercial LCs (S200 and E7), respectively. The dielectric constants of the mixture LCs were measured using the frequency selective surface (FSS) in the region from 90 to 140 GHz. We compare the simulated results with the experimental measurements and determine the dielectric constants of the LCs. The dielectric anisotropy (Δε) of the nematic S200-2 and E7-2 LC mixtures are 16.4% and 16.3% higher than that of the commercial S200 and E7 LCs, respectively. The results show the frequency tunability of the two LC mixtures is greater than that of the commercial LCs.