Methanol-water System Research Articles

On the characterization of electrified interface

Estimation of zeta potential from experimental data on electroosmotic and electrophoretic effects for Zeokarb 225 (Na+ form)/methanol-water system has been made and discussed. Results indicate that zeta potentials estimated from electroosmotic flux and electrophoretic mobility are not in agreement and vary with applied potential difference in a linear manner. Reasons for the variation of zeta potential with electrical field have been discussed. It has been argued that zeta potentials estimated from electroosmotic data are more reliable in comparison to the values obtained from electrophoretic data.

Liquid Chromatography in Pharmaceutical Analysis XI: Determination of Muscle Relaxant-Analgesic Mixtures Using Reversed-Phase and Ion-Pair Techniques

High-pressure liquid chromatography using reversed-phase and/or ion-pair techniques was used to optimize resolution of aspirin-containing muscle relaxant mixtures as well as other therapeutic agents commonly found in muscle relaxant-analgesic mixtures. The compounds were chromatographed on an octadecylsilane column using methanol-water solvent systems, some of which contained tetrabutylammonium cation as counterion. Mixtures of methocarbamol-aspirin and chlorzoxazone-acetaminophen were selected to demonstrate separation and quantification. The methocarbamol-aspirin mixture was chromatographed with methanol-water (40:60, pH 6.8) containing 0.01M tetrabutylammonium cation at a flow rate of 2.0ml/min. The chlorzoxazone-acetaminophen mixture was chromatographed with methanol-water (50:50) at a 2.0-ml/min flow rate. The separation and quantitation of each mixture were achieved in approximately 8min with accuracy in the 2–3% range.

Selective measurements of the self-diffusion coefficients in acetic acid-water and methanol-water systems by pulsed-gradient fourier-transform NMR

Measurement of the self-diffusion coefficients was performed for the binary liquid mixtures acetic acid—water and methanol—water by the pulsed-field-gradient method over the whole concentration range at 32°C. The self-diffusion coefficient of each component was determined from the Fourier-transformed spectra of proton echo signals by means of a conventional Fourier-transform NMR system. In the methanol—water system a minimum of the self-diffusion coefficient of water appeared at mole fraction 0.4, and that of methanol appeared at mole fraction 0.25. In the acetic acid—water system the self-diffusion coefficient of water did not show a minimum, and the values were nearly constant above mole fraction 0.5. The self-diffusion coefficients of water in both mixtures were larger than those of solutes over the whole concentration range. The long-lived hydrated complexes do not exist in the acetic acid—water system.

Ionic Equilibria in Mixed Solvents. XII. Hydrolysis of Cadmium(II) Ion in Dioxane–Water and Methanol–Water Mixtures

Abstract The hydrolytic reactions of cadmium(II) ions were studied at 25 °C in dioxane–water and methanol–water mixtures with varying compositions of the organic solvents, each mixture containing 3 mol dm−3 (Li)ClO4 as an ionic medium. Emf measurements were carried out over the range of the total cadmium(II) concentrations of 0.2 to 0.8 mol dm−3 in all the systems. Two complexes Cd2OH3+ and CdOH+ were found in the dioxane–water mixtures, but the latter complex was not detected in the methanol–water system. The formation constant of the Cd2OH3+ complex was slightly larger in the methanol–water mixtures than in the dioxane–water mixtures at the same mole-fraction concentration of the organic solvents.

The Detemination of the Formation Constants of the Triiodide Ion in Water–Alcohol Mixed Solvents at Various Temperatures

Abstract The formation constants of the triiodide ion were determined in water-alcohol mixed solvents by a spectro-photometric method at various temperatures. The formation reaction of the triiodide ion from an iodide ion and an iodine molecule is accompanied by a negative enthalpy change and a positive entropy change at various alcohol contents: ΔH°/kJ mol−1, −15.4 (in water) to −14.3 (in methanol) in the water–methanol system, −15.4 (in water) to −21.4 (in ethanol) in the water–ethanol system; ΔSx°/J K−1 mol−1, 36 (in water) to 57 (in methanol) in the water–methanol system, and about 36 at various ethanol contents in the water-ethanol system. The enthalpy term is the dominant factor in the water–ethanol mixtures, whereas the entropy term is the dominant factor in the water–methanol mixtures. In order to explain the thermodynamic behavior, the changes in the solvation properties as well as the activity coefficients of solutes must be considered in both the mixture systems.

Simultaneous heat and mass transfer in binary distillation—II: Experimental

A theoretical study of simultaneous heat and mass transfer in binary distillation has shown that heat and mass transfer coefficients can be appropriately evaluated if liquid phase temperatures and compositions are measured as functions of height in a column. In this study, the experiments were carried out in a wetted-wall column using a methanol-water binary system at one atmosphere.Special probes were designed to determine the state of the liquid phase. Temperatures were measured with microthermocouples and liquid samples were analyzed with a high precision refractometer. The liquid phase was found to be saturated which indicated, in accordance with the conclusions from a theoretical study, that all the resistance to mass transfer was in the vapor phase. Local transfer coefficients were calculated using the composition data as a function of column height. The results were correlated by an equation showing close agreement with the Chilton-Colburn equation. kyamV = 0.039Scy−23Rey−0.20 cm−1.It is concluded that mass transfer in the vapor phase is the controlling resistance in distillation and that there is no additional evaporation within the liquid phase caused by heat transferred from the vapor phase as proposed by some previous investigators.

Rapid Screening Method for Aflatoxins and Zearalenone in Corn

The methanol-water extraction system used in AOAC Method II for aflatoxins extracts both the aflatoxins and zearalenone from corn. Using this methanol-water extraction system as a base, a rapid screening procedure has been developed for these mycotoxins. The methanol-water extract is defatted with hexane and the pigments are precipitated with copper carbonate. The aflatoxins and zearalenone are subsequently extracted into chloroform and are then detected by half-plate TLC. An elapsed time of about 1 hr is required to analyze 1 sample. The sensitivity of the method is about 2 mu-g/kg for aflatoxin B-1 and 100 mu-g/kg for zearalenone.

Distillation Performance of Beehive Packings

Using beehive packings which were regular and had nowall effect, a relationship between HOG and the reflux ratio γ (1 to ∞) was observed. Experimental conditions were as follows; tower diameter : 78 mm, packed height : 500 mm, sample : methanol-water system, determination of vapor concentration : differential condensation temperature method. HOG varies largely depending on r when r is less than 10 and mass velocity of vapor G is less than 60% of flooding velocity. This relation can be expressed by the following equations : packing A (ε = 0.92) HOG = 0.99 γ-0.82packing B (ε = 0.90) HOG =0.01 G 0.45 γ-0.47When γ is greater than 10, HOG approaches the values at total reflux.

Study of the interaction of water with other protic solvents by paper chromatography

Interaction in the methanol-water system has been studied (i) by the measurement of the mobile phase migration rate in mixed solvents of different composition and (ii) by the changes in chromatographic behaviour of hexacyanoferrate (III) and (II) anions produced by the solvent system. The formation of semi-, mono-, di-, and trihydrates of methanol has been observed. Paper chromatographic separation of hexacyanoferrate (III) and (II) anions has been achieved in the concentration range 85 to 65% (v/v) aqueous methanol, used as a mobile phase.

Some ionic reactions in frozen, organic matrices

The radiothermoluminescence (RTL) spectra of organic frozen compounds such as methanol, acetone and several hydrocarbons are presented and discussed. Some evidence concerning the negative species responsible for RTL emission and the mechanism of excited-state formation is given. A satisfactory correlation between the temperature of RTL peaks and phase transition points has been found for the methanol-water system as well as for acetone. Additional experimental results are provided concerning the tunnelling hypothesis as a best approach to the kinetics of electron decay in 3-MP glass in the presence of biphenyl and for isothermal radioluminescence (IRL) decay observed at 77 K in such systems as acetone, ethyl acetate and methylcyclohexane. The temperature and viscosity effects on electron decay in organic glasses are pointed out.

Cooperative effects involved in esterolytic reactions of cationic long chain esters catalyzed by benzimidazole-containing polymers

The solvolyses of positively charged esters with varying chain length catalyzed by benzimidazole, poly[5(6)-vinylbenzimidazole] and copolymers of 5(6)-vinylbenz-imidazole with acrylic acid were studied. Poly[5(6)-vinylbenzimidazole] showed a marked selectivity for the positively charged esters with varying aliphatic chain length but the catalytic activity was suppressed. In order to investigate the more detailed characteristics of the 5(6)-vinylbenzimidazole-acrylic acid copolymers in the solvolyses of these esters, the effects of copolymer composition on their catalytic activities were studied. In the solvolyses of every ester employed, the copolymer compositions affected their catalytic activities. In 40% 1-propanol-water the activities of the copolymers indicated a strong dependence on the carboxylatebenzimidazole-carboxylate triad. These effects were due to strong electrostatic interactions between these sequences and the substrates. The effects of solvent composition on the catalytic activities of the copolymer-catalyzed solvolyses were also investigated. The copolymers of 5(6)-vinylbenzimidazole with acrylic acid were found to have entirely different characteristics in methanol-water than in 1-propanol-water systems. The catalytic ability was found to be a function of the benzimidazole content and on the size of the substrate. Apolar interactions became a dominant force in the methanol-water system.

Complexation of polyvinyl acetate with iodine

Polyvinyl acetate and iodine form a characteristic red complex in the presence of potassium iodide. Spectrophotometry of the complex at 510 nm in a methanol—water system at 20° yields linear calibration curves over the range 25–100 mg of polyvinyl acetate per 1. of final solution. The limit of detection is 0·1 mg of polyvinyl acetate in 0·5 ml of initial sample. Replacement of acetate groups by inert groups reduces the sensitivity of the method, and other details of the system are discussed.

Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part 15.—Free energies of transfer of cadmium chloride from water to 10–40%(w/w) methanol-water mixtures at 25°C; dissociation of CdCl+; use of dilute cadmium amalgam electrodes. The group II cations.

The cell Cd(Hg)∣ CdCl2∣ AgCl—Ag has been used to obtain the standard molar free energies of transfer, ΔG°t, of cadmium chloride from water to 10%, 20% and 40%(w/w) methanol-water mixtures. Cadmium chloride is a weak electrolyte. This was allowed for in computing the standard e.m.f. values of the cell; dissociation constants of CdCl+ were also determined. The behaviour of the Group II cations, Cd2+, Zn2+, Sr2+ and Ba2+, in the methanol-water system is discussed in terms of the “acid-base” theory and their “hardness” or “softness” as Lewis acids, and they are briefly compared with the univalent cations of Group I.

Univalent cation-exchange in organic solvent water and organic solvent-water-phenol mixtures

Selectivity coefficients, K H M, for the exchange of alkali metal ions and ammonium ions with the hydrogen form of ZeoKarb 225 cation-exchange resin have been determined in various organic solvent-water and organic solvent-water-phenol mixtures. There is an increase in K H M in passing from purely aqueous conditions to media of increasing organic solvent content, frequently with the effect of producing magnified differences and selectivity reversals between one ion and another. The results are discussed in terms of the relationship between K H M and the reciprocal of the dielectric constant of the medium and also in the light of free energies of transfer of cations between methanol-water systems. The effect of phenol giving a lowering of K H Cs in methanol-water, of K H K and K H Na in ethanol-water and of K H Na and K H L1 in acetone-water systems cannot be fully reconciled with the mechanism involving ▪ bonding proposed by earlier workers.

Effect of solvent structure on the transport of water in methanol–water–alkali-metal halide systems

In the methanol–water system, the Washburn number of water, ww, in alkali-metal halide solutions is inflected with respect to solvent composition; particularly pronounced maxima are observed for sodium iodide at ca. 15 and 40%(w/w) methanol.

Reactivity of Solvated Electrons in Radiolyzed Cyclohexane, Cyclohexane-2-Propanol and Methanol-Water

Hammett's reaction constants for the reactions of solvated electrons with substituted chrolobenzene series are 0.7 and 2.5 in cyclohexane-2-propanol and methanol-water systems respectively. The simple relation observed in alcoholic solvents between Hammett's reaction constants and the dielectric constant fails to apply to the present systems. These findings can be semi-quantitatively explained as being a result of the closer correlation presented by Hammett's reaction constants to the transition energy for the optical excitation of solvated electrons rather than to the dielectric constants of the medium.

Cellulose graft copolymers. IV. Graft copolymerization of methacrylonitrile with γ‐irradiated cellulose from DMSO–, acetone–, and methanol–water systems

AbstractMethacrylonitrile was graft‐copolymerized from DMSO–, acetone–, and methanol–water systems with γ‐irradiated, purified cotton cellulose. The relative extents of scavenging of the free radicals in the irradiated cellulose after immersion in the solvents for 3 min at 25°C, as determined by electron spin resonance spectroscopy, were: methanol (77%) > water (70%) ≫ acetone (5%) > DMSO (0%). After immersion of irradiated cellulose in the solvents for 60 min at 25°C, the relative extents of scavenging of the radicals were: methanol, water (80–85%) > DMSO (80%) > acetone (62%). From these data, it would appear that the overall rates of diffusion of methanol and water into the fibrous macrostructure were greater than the rates of diffusion of DMSO and acetone into the structure. The relative radiochemical yields of the graft copolymerization reactions of methacrylonitrile with irradiated cellulose in the different solvents were: water ≫ DMSO > methanol ≫ acetone. The addition of water to the systems increased the yields of the reactions.

蒸留理論を学ぶための教材実験 : 水-メタノール系蒸留曲線を作る

蒸留理論を学ぶための教材実験 : 水-メタノール系蒸留曲線を作る

Ion exchange equilibria in synthetic zeolite 4 A in a mixed solvent system

The ion exchange behaviour of alkali metal ions on synthetic zeolite 4 A in the water-methanol system has been studied as a function of D, the macroscopic dielectric constant of the external solution. The anomalous behaviour of Li + in the presence of organic solvent is observed. Applying a statistical-thermodynamic treatment, thermodynamic equilibrium constants are determined; from these the standard free energies of exchange are evaluated for the systems Na + ↔ M + ( M + = Li +, K +, Rb +and Cs +) in a 50 mole % water-methanol mixture. The thermodynamic affinity sequence, based on the standard free energies of exchange, is Na + > K + > Rb + > Cs + > Li +.

Cellulose graft copolymers. III. Effects of oxygen on graft copolymerization of ethyl acrylate with γ‐irradiated cellulose

AbstractThe effects of oxygen on graft copolymerization of ethyl acrylate from methanol–water systems with γ‐irradiated fibrous cotton cellulose were investigated by electron spin resonance spectroscopy and by the formation of cellulose–poly(ethyl acrylate) copolymer. The concentrations of free radicals in cellulose irradiated dry in an atmosphere of nitrogen at 25°C decreased during postirradiation storage in nitrogen or oxygen. The concentration of free radicals in the irradiated cellulose, moisture regain of the irradiated cellulose, and formation of cellulose–poly(ethyl acrylate) copolymer decreased with increase in temperature and time of postirradiation storage and to a greater extent when stored in oxygen rather than in nitrogen. From the decrease in moisture regain of irradiated cellulose during postirradiation storage, it was concluded that increased intermolecular bonding occurred in irradiated cellulose during storage in both nitrogen and oxygen atmospheres. When irradiated celluloses which had been stored in either oxygen or nitrogen were copolymerized with ethyl acrylate at 60°C, less formation of copolymer was observed than when the copolymerization reactions were conducted at 25°C. It was concluded that there was no evidence for the formation or decomposition of cellulose peroxides during these reactions and that formation of graft copolymer depended primarily on the concentration of free radicals in the irradiated cellulose at the time of copolymerization.