Dioxane Water Research Articles

Complex formation of 18-crown-6 with metal cations and ammonium ions in dioxane–water mixtures

The complex formation of 18-crown-6 with some alkali, alkaline earth, and ammonium ions in dioxane–water mixture has been studied by means of calorimetric titrations. The stability constants, reaction enthalpies and entropies for the complex formation in mixtures of water and dioxane at various proportions have been measured. The results clearly indicate the preferential solvation of the alkali and alkaline earth cations by water molecules. Thus, the values of the reaction entropies for a given cation are independent of the solvent composition. In the case of ammonium ions, the formation of hydrogen bonds between the NH-groups of the ammonium and mono and di-substituted ammonium cations and the water molecules has a pronounced influence upon the thermodynamic values measured. The results strongly demonstrate the influence of solvent composition and of selective solvation of cations in dioxane–water mixtures on the complex formation of 18-crown-6 with cations.

The Acidity and Solvation of Lignin-Related Phenols in Water—1,4-Dioxane Mixtures

The pKa values were determined for 10 guaiacyl phenols by UV spectrophotometric and potentiometric titration in the water—dioxane binary system over the composition range 0–80% organic solvent. The differentiating action of the solvent and para-substituent effects on the acidity of guaiacol derivatives were analyzed. The dependences of acidity constants on the mixed solvent composition were interpreted using the preferential solvation model.

Relationships between structure, retention and biological activity of some Schiff base ligands and their complexes

The lipophilicity of a series of Schiff base ligands and their complexes with nickel(II) and copper(II) has been determined by reversed-phase thin-layer chromatography using binary dioxane-water mobile phase. Chelate ligands were prepared by condensation of diamine and the corresponding beta-diketone. Copper(II) and nickel(II) complexes with chelate ligands containing ethane-1,2-diamine or propane-1,2-diamine as the amine part and pentane-2,4-dione and/or 1-phenylbutane-1,3-dione, pentane-2,4-dione and/or 1,1,1-trifluoropentane-2,4-dione, or 1,1,1-trifluoropentane-2,4-dione and/or 1-phenylbutane-1,3-dione as the beta-diketone part were synthesized. Some of investigated compounds were screened for their in vitro antifungal activity against Sacharomyces cerevisiae and antibacterial activity against Escherichia coli. Chromatographically obtained lipophilicity parameters were correlated both with calculated n-octanol-water partition coefficient C log P and antimicrobial activities. Satisfactory correlations were obtained. Chromatographic data proved to be reliable parameters for describing the lipophilic properties of the investigated compounds. Additionally, the principal components analysis was performed on the data chromatographically obtained. This statistical method was useful for distinguishing compounds and objective comparison of their lipophilicity parameters.

Estimation of ion pair formation constants of lithium salts in mixtures of glymes and 1,4-dioxane

This paper presents data coming from 19F NMR spectroscopy and conductivity measurements used as two independent methods for the determination of ion pair formation constants. The studied systems were limited to lithium tetrafluoroborate and trifluoromethylsulfonate solutions in mixtures of 1,4-dioxane and glyme, diglyme or water. The systems containing glyme and diglyme have coordinating properties (donor and acceptor numbers) very similar to liquid poly(ethylene glycol) dimethyl ether and solid poly(ethylene oxide) and their composition can be tailored to have the dielectric constants similar to those of the polymeric systems. The obtained results are compared with the electrochemical and spectroscopic data found in the literature for liquid poly(ethylene glycol) dimethyl ether and solid poly(ethylene oxide). The main stress of the discussion is focused on ion–ion and ion–solvent interactions and the influence of the oligooxyethylene chain length on ionic pair formation. Additionally, on the basis of the electrochemical data for the dioxane–water solutions, the difference in behavior between water-free and water containing samples of similar polarity is discussed. To check the influence of the cation on ion pairing, a similar set of experiments was performed for tetraalkylamonium salts with identical anions.

Synthesis and electrochemical sensing behaviour of a new ferrocene functionalized tet ‘a’ macrocyclic receptor towards transition metal ions

AbstractA new ferrocene functionalized macrocyclic receptor 1,8‐bis(ferrocenylmethyl)‐5,5,7,12,12,14‐hexamethyl‐1,4,8,11‐tetraazacyclotetradecane (R) has been designed and synthesized to study its potential application as chemosensor. The receptor has been characterized by spectral techniques and X‐ray diffraction. The compound crystallizes in the orthorhombic space group Pcab with four molecules in a unit cell (half‐a‐molecule in the asymmetric unit). The electrochemical studies of the receptor in dioxane–water (7:3 v/v, 25 °C) indicate that the receptor is pH‐dependent with a displacement of E1/2 to more anodic potentials with a decrease in the pH from 12 to 5. The electrochemical behaviour of R was also studied in the presence of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+ in dioxane–water (7:3 v/v, 25 °C, [Bun4N][ClO4]), showing that upon complexation the ferrocene–ferrocenium half‐wave potential shifts anodically in relation to that of the free receptor. The maximum electrochemical shift (ΔE1/2) of 46 mV was found in the presence of Cu2+, followed by Co2+ (20 mV), Mn2+ (15 mV), Ni2+ (13 mV) and Zn2+ (9 mV). Moreover, the receptor R is able to electrochemically and selectively sense Cu2+ in the presence of the other transition metal cations studied. Copyright © 2007 John Wiley & Sons, Ltd.

Kinetics of base hydrolysis of α‐amino acid esters catalyzed by the copper(II) complex of N,N,N′,N′‐tetramethylethylenediamine (Me4en)

AbstractThe kinetics of base hydrolysis of glycine‐, histidine‐, and methionine methyl esters in the presence of [Cu‐Me4en]2+ complex is studied in aqueous solutions and in dioxane–water solutions of different compositions at T = 25°C and I = 0.1 mol dm−1. The kinetics of base hydrolysis of glycine and methionine methyl esters is studied at different temperatures. The kinetic data fits assuming that the hydrolysis proceeds in one step. The activation parameters for the base hydrolysis of the complexes are evaluated. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 737–745, 2006

Ozone–dioxane delignification from the cell walls of Japanese cypress (Chamaecyparis obtusa Endl.)

Delignification from the cell walls with a combination of ozone oxidation and dioxane–water extraction using thin sections of a softwood, Japanese cypress (Chamaecyparis obtusa Endl.), was studied to determine its suitability for the production of recyclable cellulose-based materials from wood waste. The visible-light absorption spectra of treated wood sections revealed that delignification from the cell walls with ozone increased with increasing ozonization time. Ozone delignification proceeded from the lumen side toward the middle lamella within the secondary wall of a cell, and it proceeded faster in early wood than in late wood within an annual ring. Mild ozonization for 10–30 min was sufficient for the removal of lignin from the cell walls when sections were extracted with dioxane after ozonization. The results obtained here demonstrate that microspectrometry coupled with the Wiesner reaction is useful for the quantitative analysis of lignin in cell walls.

Ionic condensation of sodium chondroitin sulfate in water–dioxane mixture

In a previous work, we have verified that sodium chondroitin sulfate in water at 25 °C, presents a correct Manning behavior ( α M = 0.81). In contrast, we expect that the rate of condensation α is shifted from its Manning value ( α M = 0.36) in water–dioxane (50% wt) mixture at 25 °C, ( α ≅ 0.47). In order to verify this dioxane effect, we have compared experimental equivalent conductibility Λ exp of sodium chondroitin sulfate in water ( no shift) and water–dioxane (50% wt) mixture ( positive shift), to their theoretical values Λ M, Λ c th and Λ s th corresponding respectively to the Manning cylindrical and spherical models. Indeed, except some cases, α must obey to Ostwald's principle of dilution ( α → 1 when C Na + → 0), according to the following “rod-like model” approximation: ( 1 − α ) ≈ | Z i | ( π b S ) [ 4 ⁢ π Z i 2 L b ] [ − b S ″ α ] [ α C i R 2 ] [ 1 − b S ″ α ] ; with : b S ″ = α M − 1 However, only in pure water at 25 °C ( ε = 78.3), the exponent [1 − b S″ α] of sodium chondroitin sulfate is zero and therefore: α = α M.

Laboratory Characterization of a Commercial Capacitance Sensor for Estimating Permittivity and Inferring Soil Water Content

Ring‐capacitor sensors are used widely for real‐time estimation of volumetric soil water content θ from measured resonant frequency fr, which is directly affected by the bulk soil permittivity ε. However, the relationship fr(ε) requires improved quantification. We conducted laboratory experiments to characterize the response of the Sentek EnviroSMART sensor system for a full range of ε values from air to water and a range of temperatures. Water–dioxane mixtures were placed into a solvent‐resistant container equipped with custom tools for heating and mixing the fluid, removing air bubbles from sensitive surfaces, measuring permittivity in situ, and creating an axisymmetric metal disturbance to the electric field. Total capacitance C was measured using a vector network analyzer (VNA) connected to one sensor, while four other sensors provided replicated fr readings. The measured temperature response of free water permittivity was linear with a negative slope, which is qualitatively consistent with theory. A precise nonlinear relationship between ε and normalized fr was derived. The instrumental error in ε was RMSEε = 0.226 (for 3 < ε < 43), which corresponds to a measurement precision in θ(ε) derived from Topp's equation of RMSEθ= 0.0034 m3m−3 Axisymmetric numerical simulations of the electric field supplemented the experimental results. The characteristic length scale for the distance measured radially from the access tube is 12.5 mm, meaning that 80 and 95% of the signal are sensed within approximately 20 and 37 mm of the access tube, respectively. The results are crucial for scientific applications of the investigated sensor type to environmental media.

Solubility in the Systems MCl (M = Na, K)–1,4-Dioxane–Water at 25 ^C

Phase equilibria in the ternary systems, sodium chloride–dioxane–water and potassium chloride–dioxane–water, have been studied at 25 ^C and a section method for the determination of the immiscibility boundary has been tested. The phase diagrams exhibit the difference between the two systems. In the sodium chloride system an area of two liquid phases occurs, whereas with potassium chloride only a smooth solubility curve exists.

Synthesis and Characterization of Polydentate Schiff-Base Ligands and Their Complexes

Abstract In this study, we synthesized the amine compounds 2-{(E)-[(2-aminoethyl)imino]methyl}phenol (H3A) and 2-{(E)-[(3-aminopropyl)imino]methyl}-6-methoxyphenol (H3B) as the starting materials. From reactions of the starting materials with 2-hydroxy-5-methylisophthalaldehyde, phthalaldehyde, and 2-hydroxy-5-t-butylisophthalaldehyde, we prepared the new ligands H3L1–H3L3 and H2L. The Cu(II) and Cd(II) complexes of the ligands have been obtained. Microanalytical data, magnetic moment, 1H(13C) NMR, mass spectra, FT-IR, and conductivity measurements have been used to explain the structures of the ligands and their complexes. The protonation constants of the ligands H3L1–H3L3 have been studied in a 1:1 molar ratio (M:L). Protonation and stability constants of the Schiff bases and their Cu(II) and Cd(II) complexes have been determined by the potentiometric titration method in 50% dioxane–water media at 25.00 ± 0.02 °C under a nitrogen atmosphere and ionic strength of 0.1 M NaClO4. The ligands H3L1–H3L3 have seven protonation constants. In other words, the ligand H2L has six protonation constants. The variation of protonation constants of these compounds were interpreted on the basis of structural effects exposed by the substituents.

Simultaneous lower and upper critical solution temperature‐type co‐nonsolvency behaviour exhibited in water–dioxane mixtures by linear copolymers and hydrogels containing N‐isopropylacrylamide and N,N‐dimethylacrylamide

AbstractThe co‐nonsolvency behaviour in water–dioxane mixtures of linear copolymers and hydrogels consisting of N‐isopropylacrylamide (NIPAM) and N,N‐dimethylacrylamide (DMAM) was studied as a function of solvent composition and temperature. The composition of the copolymers, P(NIPAM‐co‐DMAMx), in DMAM units, x, varies from x = 0 up to x = 100%. It is shown that the copolymers combine the lower critical solution temperature (LCST)‐type co‐nonsolvency behaviour of poly‐NIPAM with the upper critical solution temperature (UCST)‐type co‐nonsolvency behaviour of poly‐DMAM. Depending on x, both the LCST‐ and UCST‐type co‐nonsolvency behaviour may be simultaneously observed in water‐rich and dioxane‐rich solvent mixtures, respectively. Due to this complex phase separation behaviour, the variation of the reduced viscosity of the linear copolymers, as well as the swelling–deswelling behaviour of the respective hydrogels, are shown to be temperature‐ and solvent‐sensitive. Copyright © 2006 Society of Chemical Industry

Solubility parameter of drugs for predicting the solubility profile type within a wide polarity range in solvent mixtures

The solubility enhancement produced by two binary mixtures with a common cosolvent (ethanol–water and ethyl acetate–ethanol) was studied against the solubility parameter of the mixtures ( δ 1) to characterize different types of solubility profiles. Benzocaine, salicylic acid and acetanilide show a single peak in the least polar mixture (ethanol–ethyl acetate) at δ 1 = 22.59, 21.70 and 20.91 MPa 1/2, respectively. Phenacetin displays two solubility maxima, at δ 1 = 25.71 (ethanol–water) and at δ 1 = 23.30 (ethyl acetate–ethanol). Acetanilide shows an inflexion point in ethanol–water instead of a peak, and the sign of the slope does not vary when changing the cosolvent. The solubility profiles were compared to those obtained in dioxane–water, having a solubility parameter range similar to that covered with the common cosolvent system. All the drugs reach a maximum at about 90% dioxane ( δ 1 = 23 MPa 1/2). A modification of the extended Hildebrand method is applicable for curves with a single maximum whereas a model including the Hildebrand solubility parameter δ 1 and the acidic partial solubility parameter δ 1a is required to calculate more complex solubility profiles (with inflexion point or two maxima). A single equation was able to fit the solubility curves of all drugs in the common cosolvent system. The polarity of the drug is related to the shape of the solubility profile against the solubility parameter δ 1 of the solvent mixtures. The drugs with solubility parameters below 24 MPa 1/2 display a single peak in ethanol–ethyl acetate. The drugs with δ 2 values above 25 MPa 1/2 show two maxima, one in each solvent mixture (ethanol–water and ethanol–ethyl acetate). The position of the maximum in ethanol–ethyl acetate shifts to larger polarity values (higher δ 1 values) as the solubility parameter of the drug δ 2 increases.

Reactions of elemental phosphorus and phosphine with electrophiles in superbasic systems: XVIII. Phosphorylation of 1-(chloromethyl)naphthalene with the elemental phosphorus

1-Chloromethylnaphthalene reacts with white and red phosphorus, and also with the “activated red phosphorus,” the complex organophosphorus polymer of unknown structure obtained by irradiation of a solution of white phosphorus in benzene by the 60Co source, in a system including KOH water solution, dioxane or benzene, and a phase transfer catalyst (22–98°C, argon), to form bis(1-naphthylmethyl)-and tris-(1-naphthylmethyl)phosphine oxides, and also (1-naphthylmethyl)phosphonous-and bis(1-naphthylmethyl)-phosphinic acids. The yield and the ratio of the reaction products depend on reaction conditions as well as on the nature of phosphorylating agent. It is shown that the reactivity of the “activated red phosphorus” is not worse than that of the white phosphorus and significantly exceeds the reactivity of the usual technical red phosphorus.

Micellar effects on the molecular aggregation and fluorescence properties of benzazole-derived push–pull butadienes

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-( p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in dioxane–water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties (such as polarity and CMC) have been determined using both dienes as probes.

Dielectric relaxation of dioxane-water mixtures using time domain technique

The complex permittivity of dioxane in water mixtures for various concentration and temperatures have been measured as a function of frequency between 10 MHz to 20 GHz using time domain reflectometry technique. Dielectric relaxa-tion parameters i.e. static dielectric constant and relaxation time were obtained from the complex permittivity spectra using the nonlinear least square fit method. The relaxation behaviour of these mixtures are explained by the Debye model. The Debye relaxation time of the mixture shows a maxima for the mixture with 40% of water by volume. This suggests that the tendency to form cluster between water and dioxane molecules is maximum for this mixture. The Kirkwood correlation factor, excess permittivity and Bruggeman factor have been determined at various concentration of water in dioxane.

Synthesis, characterisation and polar effect of the substituent on the reaction mechanism of 3-aminophenyl phosphate esters

The kinetics and mechanism of the acid hydrolysis of 3-aminophenyl phosphate esters have been studied in 0.1 to 6.0 mol dm -3 HCl at 90 ± 0.5 °C. The effects of temperature, solvent and substrate concentration on the rate of hydrolysis have been studied and the results suggest that the hydrolysis of monoester occurs by the cleavage of P-O bond fission. The rate coefficients estimated are fairly in good agreement with the experimentally observed ones. Bond fission, molecularity and order of reaction have been supported by Arrhenius parameters, Zucker-Hammett hypothesis, concentration, solvent effect etc. A study of the reaction in dioxane water mixture suggested the nature of transition state in which charges are developed due to the bimolecular attack of water molecule. Comparative isokinetic rate data of similarly substituted phenyl phosphate monoesters, whose mechanism is known, supported P-O bond fission.

Thermodynamics of electrolytes in mixed solvent media — Application of the Pitzer ion interaction approach

Although for a long time considerable attention has been paid to the application of the Pitzer ion interaction approach to describe the thermodynamic properties of a variety of aqueous electrolyte solutions, such studies in mixed solvent media are still scarce. The present paper discusses the application of the Pitzer ion interaction approach in the case of electrolyte solutions in mixed solvent media. In particular, a comprehensive equation for the thermodynamic properties of hydrochloric acid in dioxane–water mixtures within the temperature range 273.15 to 323.15 K has been generated in the ion interaction (Pitzer) equation form on the basis of electrochemical cell measurements of the hydrochloric acid available in the literature. It was necessary to set varying values of the exponential coefficients α1 and α2 of the standard Pitzer model in different mixed solvent media to achieve a satisfactory fit. The present model quantitatively reproduces the experimental cell electromotive forces over the entire concentration and temperature range used for the experiments. The Pitzer ion interaction approach is, thus, proved to be a very valuable method for the correlation and prediction of thermodynamic properties of electrolytes in mixed solvent media. The implications of the Pitzer ion interaction parameters (β(0), β(1) β(2), and Cϕ) have also been discussed in terms of interionic forces. The present study also stresses the need for additional emf measurements to help interpolation through the dioxane composition. Key words: Pitzer's equations, Pitzer ion interaction parameter, activity coefficients, emf, hydrochloric acid.

Control of the lower critical solution temperature—type cononsolvency properties of poly( N-isopropylacrylamide) in water—dioxane mixtures through copolymerisation with acrylamide

The behaviour of the homopolymers poly( N-isopropylacrylamide) (PNIPAM), polyacrylamide (PAM) and random copolymers of N-isopropylacrylamide (NIPAM) with acrylamide (AM) was studied by turbidimetry and viscometry in mixtures of water with dioxane. It was found that the well-known lower critical solution temperature-type cononsolvency properties of PNIPAM in water–dioxane mixtures, observed in the water-rich region, can be effectively controlled by copolymerisation of NIPAM with AM. Thus, the cononsolvency properties of the copolymers in water–dioxane mixtures are shifted to higher temperatures and restricted within a narrower solvent composition region as the acrylamide content of the copolymers increases. A significant decrease of the reduced viscosity of the systems exhibiting phase separation properties was observed upon heating, indicative of the collapse of the (co)polymer chains as temperature approaches the corresponding cloud point temperature. Furthermore, when temperature is fixed close to the cloud point temperature, the reduced viscosity decreases with increasing the volume fraction of dioxane, φ, as far as the solvent mixtures are rich in water. On the contrary, the reduced viscosity of PNIPAM in dioxane-rich mixtures is found significantly higher, indicative of an expansion of the polymer chain, as compared to the reduced viscosity of this polymer in the two pure solvents.

Self-association of free base porphyrins with aminoacid substituents in AOT reverse micelles

The aggregation properties of aminosulfonyl porphyrins with aminoacid substituents: methionine with the acid function methylated, PMe t C H 3 ; phenylalanine, PPhe; attached to the para positions of the meso phenyls of the porphyrin, was followed in organic solvents, water–dioxane mixtures and in reverse micelles of aerosol OT (AOT RM), using absorption, steady-state and time-resolved fluorescence. In AOT RM in the absence of water, both porphyrins are mainly present as monomers with the Soret band around 420 nm and with emission maxima around 649 and 717 nm. In the presence of water accounted for by parameter ω 0, ω 0 = [H 2O]/[AOT], the solubility of both porphyrins is enhanced and followed by important spectral changes similar to those observed in the solvent mixtures: new maxima in absorption around 405 nm and in emission around 670 nm. A concomitant increase of the aggregates’ contribution is found for PMe t C H 3 , whereas for PPhe the effect is much more pronounced until ω 0 = 10, above which a de-aggregation process occurs, due to competition between intra- and inter-molecular interactions. The small resonant light scattering signals observed points to the existence of aggregates of small dimensions whose nature is discussed in terms of exciton theory.