Dioxane Water Research Articles

Thermodynamics and ion—solvent interactions of trichloroacetic acid in 50% dioxane—water

The thermodynamics of ion-association in aqueous solutions was reviewed by Noncollas [1] in 1960. The ion-pairs of nitrates [2], halides [3–5], hydroxides [5–8], sulphates [9], acetates [2] and malonates [10] of some metal ions were studied and the thermodynamic parameters were reported. Similarly, the association data of some organic and inorganic acids [11–14] were also studied. From these studies it was concluded that the association constants may decrease or increase or may pass through a minimum with increase in temperature, but no explanation was given for the deviations observed. Hence, we have studied the thermodynamics of ion-pair formation of trichloroacetic acid in 50% (w/w) dioxane—water mixtures at different temperatures and the deviations are explained in terms of the changes in ion—solvent interactions with temperature.

Lignin and related compounds. VIII. Lignin monomers and dimers from hydrogenolysis of aspen poplar wood using rhodium-on-charcoal catalyst

Aspen poplar wood meal has been subjected to catalytic hydrogenolysis in dioxane–water (9:1) at 500 psig initial pressure of hydrogen over a 5% rhodium-on-charcoal catalyst for five hours at 195 + 5 °C. The resulting chloroform-soluble lignin degradation products were separated by cellulose and silica gel column chromatography. The following compounds were isolated and identified: 4-hydroxybenzoic acid (5), 1-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanone (propiosyringone) (6), 2,2′-dihydroxy-3,3′-dimethoxy-5,5′-dipropylbiphenyl (7), 2,3-bis(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (11), and a mixture of 3-(4-hydroxy-3,5-dimethoxyphenyl)-2-(4-hydroxy-3-methoxyphenyl)-1-propanol (9) and 3-(4-hydroxy-3-methoxyphenyl)-2-(4-hydroxy-3,5-dimethoxyphenyl)-1-propanol (10).

Thermodynamics of salts in dioxane—water mixtures from viscosity, apparent molar volume and conductance data at 35°C

Thermodynamics of salts in dioxane—water mixtures from viscosity, apparent molar volume and conductance data at 35°C

Thermodynamics of salts in dioxane—water mixtures from viscosity measurements

Thermodynamics of salts in dioxane—water mixtures from viscosity measurements

Standard potentials of the silver—silver bromide electrode in dioxane—water mixtures and related thermodynamic functions

The standard potentials of AgAgBr electrode in eighteen dioxane + water solvent mixtures containing up to 90 wt % dioxane, have been evaluated from the emf measurements of the cell Pt, H 2 (g, 1 atm); HBr (m), X % dioxane, Y % water: AgBr, Ag at nine different temperatures in the range 15–55°C. The standard molal potentials in each solvent have been represented as a function of temperature. The standard thermodynamic functions for the cell reaction, the primary medium effects of various solvents upon HBr and the standard thermodynamic quantities for the transfer of one mole of HBr from water to the respective dioxane + water media have been computed and discussed in the light of ion—solvent interactions as well as the structural changes of the solvents.

Mononuclear heterocyclic rearrangements. Part 7. Evidence for general base catalysis in the rearrangement of the Z-phenylhydrazone of 3-benzoyl-5-phenyl-1,2,4-oxadiazole into 2,5-diphenyl-4-benzoylamino-1,2,3-triazole in dioxan–water

The title reaction has been studied at various pS+ and buffer concentrations. Kinetic constants for uncatalysed and catalysed pathways have been calculated. A mechanism for the rearrangement is offered.

Studies of some ternary complexes of copper(II) involving π-bonding ligands

The formation constants of complexes of the type [CuAL]+, where A = 1, 10-phenanthroline, 2-(2′-pyridyl)benzimidazole, or 2-(2′-pyridyl)imidazoline and = MeCOCH2CONPh–(L1), MeCOCH2CONC6H4OMe-o–(L2), MeCOCH2CONC6H4Me-o–(L3), or PhCOCH2CONPh–(L4), have been determined in dioxan–water (1 : 1 v/v)solutions and 0.1 mol dm–3 Na[ClO4] at 30 °C. The value of Δ log K= log KMAL′–log KML is positive (KMAL′ is for MA + L ⇌ MAL) except when A is 2-(2′-pyridyl)imidazoline. Ultraviolet spectral studies of these complexes have also been carried out and show that there is no significant interaction between the two ligands through the metal dπ orbitals in the mixed-ligand complexes. Positive Δ log K values may be due to a lowering in repulsion between metal dπ electrons and ligand π electrons in the mixed-ligand complex.

Solvolysis mechanisms for benzyl substrates

The solvolysis of p-methoxybezyl bromide in 80%V/V dioxan–water involves trappable carbonium ion intermediates as shown by increases in rate and α-D isotope effect with increasing perchlorate ion concentation and reducations in rate and α-D isotope effect with increasing concentration of common ion salt.

A Kinetic Study on the Proton-transfer Reactions of Bis(dimethyl-glyoximato)cobalt (III) Complex Ions in Dioxane–Water Media

Abstract The proton-transfer reactions of bis(dimethylglyoximato)cobalt(III) complex ions, [CoIII(dmgH)2X2]n, with hydroxide ion, OH−, were studied in dioxane–water media by means of a temperature-jump method. The rate constant, kf, for the direct proton-transfer from [CoIII(dmgH)2X2]n to OH− was found to be 1.6×105–2.9×106 mol−1 dm3 s−1 in aqueous solution. The value of kf for [CoIII(dmgH)2(CN)2]− anion decreased gradually from 1.6×105 to 4.0×104 mol−1 dm3 s−1 for the change in the mole fraction of dioxane, xdiox, from 0 to 0.174. On the other hand, with increase in xdiox, the value of kf for [CoIII(dmgH)2(NH3)2]+ cation gradually decreased from 2.9×106 to 1.1×107 mol−1 dm3 s−1 in a region of lower xdiox, and then increased from 1.1×106 to 1.6×106 mol−1 dm3 s−1 in a region of higher xdiox. The dependence of kf on xdiox is interpreted in connection with reaction mechanism.

Thermodynamic proton—ligand stability constants in dioxane—water media. p Ka, Δ G0, Δ H0 and Δ S0 values for N- p- chlorophenyl substituted hydroxamic acids

The thermodynamic ionisation constants of N- p-chlorophenyl substituted hydroxamic acids have been determined in different mole fractions of dioxane (0.174–0.330) at 25 and 35±0.1°C. The thermodynamic parameters, Δ G 0, Δ H 0 and Δ S 0, are calculated. The effect of solvent, the change in free energy from mixed aqueous to aqueous media, δ, the Hammett correlation function and the effect of substituents on the ionisation constants of hydroxamic acids are discussed.

ChemInform Abstract: KINETIC SALT EFFECTS IN THE ACID HYDROLYSIS OF POTASSIUM ETHYL MALONATE IN WATER AND IN 50% DIOXANE‐WATER MIXTURE

The rates of the acid hydrolysis of potassium ethyl malonate in presence of KCl, NaCl, Li2SO4 and MgSO4 in water and in 50% by weight of dioxane—water mixture were measured. The concentration of the added salts covered the range 0–1M. A negative salt effect on the rate of the half-ester hydrolysis was observed. The applicability ofBronsted's equation was tested and deviations found were explained as due among other reasons, to the operation of an iondipole type of interaction. The correlation between the hydration numbers as well as the radii of the cations of the added electrolytes and the reaction rate were discussed. The activation energy was found to increase with an increase of the concentration of electrolyte due to the relative changes in solvation of the transition state as a result of hydration of the electrolytes added. The thermodynamic properties of the activated complex were calculated and discussed as functions of the salt concentration. A remarkable linear compensation between ΔH≠ and ΔS≠ was found.

Thermodynamics of ternary salts in dioxane—water mixtures from conductance measurements

Studies of electrolytic conductance in dioxane—water mixtures of varying dioxane content were initiated in 1978 [1]. In the present communication, an attempt has been made to evaluate the thermodynamic function Δ G 0 t for the transfer of Mg(ClO 4) +, Mg(NO 3) +, BaCl +, BaBr +, Ba(ClO 4 +, Ba(NO 3) +, SrCl +, Sr(NO 3) +, CaCl + and Ca(NO 3) + from water to dioxane—water media, which would give some information regarding ionic solvation.

Thermodynamics of NaCl, NaBr and NaNO 3 in dioxane—water mixtures from conductance measurements

Thermodynamics of NaCl, NaBr and NaNO 3 in dioxane—water mixtures from conductance measurements

Hydrolytic behavior of two β-lactams and their corresponding imidate salts. New evidence for stereoelectronic control

The basic hydrolysis and the concurrent carbonyl–oxygen exchange of 18O-labelled N-phenyl-4-phenyl-2-azetidinone (5*) and N-2,6-dimethylphenyl-2-azetidinone (6*) have been studied. β-Lactam 5* was easily hydrolysed and showed no carbonyl–oxygen exchange with 0.1 N sodium hydroxide (dioxane–water, 9:1). Under the same conditions, β-lactam 6* gave no exchange and was found resistant to basic hydrolysis. Hydrolysis and exchange was observed when 6* was refluxed with 0.1 N and 1 N sodium hydroxide in water.The hydrolysis of the corresponding imidate salts 7 and 8 was also investigated. Under basic conditions, salt 7 gave an 8:2 mixture of ester amine 9 and β-lactam 5, while under acidic conditions the hydrochloride salt of ester amine 9 was the only product. Under basic conditions, the imidate salt 8 produced only the β-lactam 6, and under acidic conditions, a 3:7 mixture of the hydrochloride salt of 10 and β-lactam 6. Under stronger acidic conditions (≥3 N HCl), 8 gave only the starting β-lactam 6.The results of these hydrolysis reactions are easily explained on the basis of the stereoelectronic theory for the cleavage of tetrahedral intermediates, and by taking into account that the nitrogen of tetrahedral intermediates must be either protonated under acidic conditions, or hydrogen bonded with the solvent under basic conditions in order to observe the cleavage of the C—N bond.

Thermodynamics of the silver—silver thiocyanate electrode in water—dioxane mixtures at different temperatures

In recent years, considerable effort has been devoted to physico-chemical studies in non-aqueous and mixed solvents. Most of these have been concerned with solutions in mixed solvents with a view to explaining the effect of a changing solvent composition of the ion—solvent and electrode—solvent interactions. Several workers [1–6] have presented studies of electrode—solvent interactions in water—dioxane, water—glycol, water—alcohols and water—urea mixtures of various compositions, and have reported the role of the permittivity of the medium towards such interactions. In previous studies [3,7–9], we have examined the effect of changing the solvent from pure water to 10, 20, 30 and 40 mass % dioxane + water on the dissociation of acids, dissolution of silver salts and standard potentials of the silver—silver chromate electrode. To extend the work, we now report the results of a determination of the standard potentials of the silver—silver thiocyanate electrode and associated thermodynamic parameters for the electrode reaction in these media. However, various thermodynamic quantities for the electrode reaction of this electrode and the dissolution process of silver thiocyanate are known in water [10] and formamide [11].

A Thermodynamic Study on Hydrolytic Reactions of Lead(II) Ion in an Aqueous Solution and Dioxane–Water Mixtures. I. A Potentiometric Study

Abstract The hydrolytic reactions of lead(II) ions were studied at 25 °C by means of potentiometric titrations by using a glass electrode in water and dioxane–water mixture (dioxane contents: 0.1 and 0.2 mol fractions) containing 3 mol dm−3 LiClO4 as a constant ionic medium. Four complexes, Pb3(OH)33+, Pb4(OH)44+, Pb3(OH)42+, and Pb6(OH)84+ were found in the solvent systems examined at pH\lesssim8, and the formation constant *βpq for the reaction, qPb2++pH2O=Pbq(OH)p(2q−p)++pH+, was determined. The autoprotolysis constants Ki in the same solvent systems were also obtained by use of a hydrogen electrode. The formation constant βpq(=*βpq/Kip) for the reaction, qPb2++pOH−=Pbq(OH)p(2q−p)+ was evaluated by combining the formation constants *βpq and the autoprotolysis constants obtained. The free energy change of transfer from water to a dioxane-water mixture for the reaction could be estimates as ΔGpqt=−RTln{βpq(mix)⁄βpq(aq)}. The values (1/p)ΔGpqt of hydroxo complexes of various metal ions such as lead(II), copper(II), nickel(II), beryllium(II), and cadmium(II) ions were approximately independent of the complexes at a given concentration of dioxane. This result suggested that the formal charge per metal ion of the complex, z′ (=z−p/q; z: charge of a metal ion), rather than the total charge of the complex, zq–p, is essential for the interactions between the hydroxo complexes and solvent molecules.

Benzoate catalysis in the hydrolysis of endo -5-[4′(5′)imidazolyl]-bicyclo[2.2.1]hept- endo - 2-yl trans -cinnamate: Implications for the charge-transfer mechanism of catalysis by serine proteases

The acceleration, by a factor of 2500, of the hydrolysis of endo-5-[4'(5')imidazolyl]bicyclo[2.2.1]hept-endo- 2-yl trans-cinnamate by 0.5 M sodium benzoate in 42 mol% dioxane in water can be explained without resort to operation of a "charge-relay" mechanism similar to that often postulated to account for the enzymatic activity of serine proteases. The degree of ionization of 4-methylimidazole and of sodium benzoate in 42 mol% dioxane in water at 60 degrees C have been measured by NMR spectroscopy.

Extended hildebrand approach: Solubility of caffeine in dioxane–water mixtures

The solubility of caffeine in various dioxane–water mixtures was analyzed in terms of solute–solvent interactions using a modified version of the Hildebrand treatment for regular solutions. The solubility equation employs a term (W) to replace the geometric mean (c1c2)1/2, where c1 and c2 are the cohesive energy densities for the solvent and solute, respectively. The new equation provides an accurate prediction of solubility once the interaction energy, W, is obtained. In this case, the energy term is regressed against a polynomial in δ1 of the binary mixture. A quartic expression of W in terms of the solvent solubility parameter was found for predicting the solubility of caffeine in dioxane–water mixtures. The expression yields an error in mole fraction solubility of <3%, a value approximating that of the experimentally determined solubility. The one exception to a good fit is near the maximum solubility, where a depression or valley occurs between the two peaks in solubility data; at this point, the theoretical equation predicts the solubility within ∼9%. The new model also may be used to estimate the solubility of drug molecules employing the volume fraction of water in the solvent mixture instead of the composite solubility parameter, δ1. The method has potential usefulness in preformulation and formulation studies during which solubility determination is important for drug design.

Thermodynamics of the chlorides, bromides, nitrates, bromates, iodates and sulphates of potassium and sodium in dioxane—water mixtures from conductance data at different temperatures

Studies on electrolytic conductance in dioxane—water mixtures of varying compositions at 30, 35, 40 and 45°C were initiated, in which the variations in the Walden product with solvent composition and temperature were reported and discussed with respect to theories concerning solvent structure and ion—solvent interactions. In the present communication, attempts have been made to evaluate the thermodynamic function (Δ G 0 t) for the transfer of KCl, KBr, KNO 3, KBrO 3, KIO 3, K 2SO 4, NaCl, NaBr, NaNO 3, NaBrO 3, NaIO 3 and Na 2SO 4 from water to respective dioxane + water media, which would give some information regarding ionic solvation.

Solvent effect on the rate of N(III)/Cl(V) reaction

Kinetics of the reaction between N(III) and Cl(V) have been studied in water and water–dioxan solutions. The rate equation of the reaction in each solvent could be written as[Formula: see text]and the rate rises as the dielectric constant of the medium is lowered. This observation is in accord with suggested mechanistic details involving the intermediate H2NClO5.