Water-dioxan mixtures

Solvents Other Than Water A. Water-Dioxan Mixtures 

The evaluation of these basic fractionation parameters provides a basis for the study of dioxan-H20-D20 mixtures with a constant proportion of dioxan but varying relative amounts of the isotopic waters. No significant measurements in such systems or on systems with a non-aqueous component other than dioxan appear as yet to have been reported. Hine and Haworth (1958) have successfully studied the 

The formula of the monosolvated hydrogen ion in methanol solution is assumed to be MeOHj. This is a two-proton species, compared with the three-proton species H30+ considered for aqueous solutions. Similarly the methanol molecule itself contains one exchangeable proton less than water. As a result, the characteristic equations of the theory based on the general equation (32) change in form for the MeOH-MeOD system. If we consider the dissociation of a weak acid, for example, 

The fractionation factor LA correspondingly refers to the deuterium distribution between the acid and methanol ( LA = (D/H)LA/(D/H)Me0L). From the expression for the limit - -l, we obtain 

Equations (169) to (171) are the analogues of (29) to (31) for aqueous solutions and are different from them. These expressions put in more explicit form the suggestion (Gold, 1960) that the study of acid-base phenomena in non-aqueous isotopic solvent mixtures can give information concerning the formula of the dominant form of Bronsted acid present. 

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Physical properties of the acid and its anhydride are summarized in Table 1. Other references for more data on specific physical properties of succinic acid are as follows solubiUty in water at 278.15—338.15 K (12) water-enhanced solubiUty in organic solvents (13) dissociation constants in water—acetone (10 vol %) at 30—60°C (14), water—methanol mixtures (10—50 vol %) at 25°C (15,16), water—dioxane mixtures (10—50 vol %) at 25°C (15), and water—dioxane—methanol mixtures at 25°C (17) nucleation and crystal growth (18—20) calculation of the enthalpy of formation using semiempitical methods (21) enthalpy of solution (22,23) and enthalpy of dilution (23). For succinic anhydride, the enthalpies of combustion and sublimation have been reported (24). 

Fig 3.21. Rate of oxygen removal from a ZnO film (a.u.) as a function of s of water-dioxane mixtures (verification of the equation (3.29)). 

Yakolev, Y. B. Kul ba,F. Y. Zenchenko, D. A., Potentiometric measurement of the ionic products of water in water-dimetylsulphoxide, water-acetonitrile and water-dioxane mixtures, Russ. J. Inorg. Chem. 20, 975-976 (1975). 

Carell and Olin (58) were the first to derive thermodynamic functions relating to beryllium hydrolysis. They determined the enthalpy and entropy of formation of the species Be2(OH)3+ and Be3(OH)3+. Subsequently, Mesmer and Baes determined the enthalpies for these two species from the temperature variation of the respective equilibrium constants. They also determined a value for the species Be5(OH) + (66). Ishiguro and Ohtaki measured the enthalpies of formation of Be2(OH)3+ and Be3(OH)3+ calorimetrically in solution in water and water/dioxan mixtures (99). The agreement between the values is satisfactory considering the fact that they were obtained with different chemical models and ionic media. 

Exchange of unimers between two different types of block copolymer micelles has often been referred to as hybridization. This situation is more complex than for the case described above because thermodynamic parameters now come into play in addition to the kinetic ones. A typical example of such hybridization is related to the mixing of micelles formed by two different copolymers of the same chemical nature but with different composition and/or length for the constituent blocks. Tuzar et al. [41] studied the mixing of PS-PMAA micelles with different sizes in water-dioxane mixtures by sedimentation velocity measurements. These authors concluded that the different chains were mixing with time, the driving force being to reach the maximum entropy. 

Stability Constants for Kojate Complexes m Water-Dioxan Mixtures... 

A kinetic smdy of the acylation of ethylenediamine with benzoyl chloride (110) in water-dioxane mixtures at pH 5-7 showed that the reaction involves mainly benzoylation of the monoprotonated form of ethylenediamine. Stopped-flow FT-IR spectroscopy has been used to study the amine-catalysed reactions of benzoyl chloride (110) with either butanol or phenol in dichloromethane at 0 °C. A large isotope effect was observed for butanol versus butanol-O-d, which is consistent with a general-base-catalysed mechanism. An overall reaction order of three and a negligible isotope effect for phenol versus phenol- /6 were observed and are consistent with either a base- or nucleophilic-catalysed mechanism. Mechanistic studies of the aminolysis of substituted phenylacetyl chlorides (111) in acetonitrile at —15 °C have revealed that reactions with anilines point to an associative iSN2 pathway. ... 

In order to find the influence of compression on collapse of the polymer networks, the experiments on the swelling of the deformed gels of AA-SMA in water-methanol and water-dioxane mixtures were performed [29]. It was shown that uniaxial compression of the gel really affects the swelling curves and that, in a good agreement with the theory, the region of stability of the collapsed state increases and the sharpness of collapse decreases under compression. 

Another approach attempts to explain the different effect of the ester structure in different reaction media simply by the changing ability of the esters to be absorbed by the resin. Qualitatively, this approach was used [476] to interpret the results for water and aqueous acetone and a similar idea was suggested for the hydrolysis of dicarboxylic acid esters in water—dioxan mixtures [482,483]. Quantitative interpretation was based [481,489] on Helfferich s model [427]. It follows from eqn. (30) and from the relation... 

Specifically the concentration equilibrium constant for the hydration is about 180 in water-dioxane mixtures at 25°. The main reaction for the interconversion, starting from the enol, is therefore ... 

Aptel et al. [40] observed a reduction of separation factor as a function of decreasing membrane thickness for grafted polytetrafluoroethylene films using a water/dioxane mixture. They have shown in a different study [41] that transport rate is inversely proportional to thicknes in the pervaporation separation of water through poly(tetra fluoroethylene)-poly(4-vinylpyridine) membranes. 

FIGURE 3.2 Variation of the solubility of a nonelectrolyte solute (caffeine) in a water— dioxane mixture. [Graph reconstructed from data by Djei et al., J. Pharm. Set, 69, 659 (1980).]... 

The fluorescence lifetimes (t determined at 580 nm) and quantum yields () of SRB were determined in water-dioxane mixtures and a series of alcohols at 25°C. The km value varied with the medium in the range of (4.1-0.7) x 10 s whereas the radiative decay rate constant (kr) was rather insensitive to the medium properties (2.8-1.7) X 10 s" . The relationship between In km and t(30) fall on a straight line and the slope value of the plot was 0.074 0.01. Therefore, the photophysical properties of SRB and Equation (20) are applicable to probing the polarity at a water/oil interface. 

Regarding water-dioxane mixtures, the maxima observed in Walden products are smaller than in water-alcohol mixtures and in these mixtures too the ions having a lower structure-breaking capacity show a higher increase in Walden products than in water. 

Table XV.5. Effect of Dielectric Constant on Dissociation op Tetrisoamyl Ammonium Nitrate (Water-Dioxane Mixtures)...

This continuum model predicts that all of these thermodynamic properties should preserve their sign and increase in magnitude as D is decreased. This is, of course, subject to the behavior of the derivatives (din D/d In T) and (din D/d In F) as D changes. In the case of weak electrolytes this is qualitatively the observed behavior. Some values are given in Table XV.7 for the dissociation of HaO and acetic acid in water-dioxane mixtures. Since the derivatives of D and F are not the same as the values in pure HaO, the values cannot be expected to follow D in any simple fashion. However, it is seen that qualitative agreement is obtained. If one uses Eqs. (XV.12.2) to (XV.12.5) and the experimental values of the derivatives for water, it is possible to calculate AFp from the experimental values of each of the thermodynamic quantities in turn. For acetic acid the values are 4.7 Kcal from AS, 0.3 Kcal from AH, 5.5 Kcal from ACp, and 5 Kcal from AF. Except for AH, this can be considered quite good correlation compared to AFion = 6.5 Kcal observed directly. For H2O the values are 4 Kcal from AS, 6 Kcal from ACp, 33 Kcal from AH, and... 

Fig. 4.107. Comparison of the concentration dependence of the equivalent conductivity of tetraisoamylammonium nitrate dissolved in water and in water-dioxane mixtures.

Fig. 4.109. Minimum in the curve for equivalent conductivity vs. concentration in the case of tetraisoamylammonium nitrate in a water-dioxane mixture of dielectric constant e = 2.56.

FIGURE 2-3 Activity coefficients calculated by the limiting Debye-Huckel equation (dotted lines) and those observed experimentally. Left, electrolytes of three charge types in water. Right, hydrochloric acid in water-dioxane mixtures with bulk dielectric constants as indicated. Adapted from Homed and Ow . )... 

In addition to the more usual application to solids, dielectric relaxation or dispersion measurements are also used on solutions (and pure liquids). Cook (425) related the relaxation mechanism in water-dioxane mixtures to the rupture of H bonds. Hasted and co-workers (890) found that water-dioxane mixtures had longer relaxation times as the dioxane proportion increased or the temperature was lowered. Both trends are explained by formation of a H bonded complex. Yasumi (2219) found similar effects when large amounts of hexane... 

H. F. Cook. Trans. Faraday Soc. 47, 751-5 (1951). Dielectric relaxation water-dioxane mixtures, 15-50 C. 

An inspection of the values of the parameter (e) (Table 1) shows that this parameter has always positive values for the systems investigated and depends on the natures of both the drug and cosolvent. Eor the solubilities of structurally related caffeine and theophyllene in aqueous A,A-dimethylformamide, the values of (e) are close to each other (45.2 and 42.8). However, the values of (e) for the stmcturally more different sulfonamides (sulfadiazine, sulfadimidine, sulfamethizole, sulfamethoxazole, sulfapyridine, sul-famethoxypyridazine, sulfanilamide, and sulfisomi-dine) in water/dioxane mixtures differ by a factor of two and even three for sulfamethizole. 

Figure 38. A, Circular dichroism spectra of -nicotinamide-adenine dinucleotide ( -NAD) as a function of temperature showing the reciprocity between the adenine band just below 260 nm and the nicotinamide band near 270 nm. These reciprocal relations in optical rotation qualitatively demonstrate a close interaction of the two aromatic rings. Reproduced, with permission, from [98]. B, Circular dichroism curves of flavin-adenine dinucleotide (FAD) as a function of water/dioxane mixtures. As the solvent becomes more polar, there is increased proximity of the two aromatic rings, as shown by the reciprocal changes in the intensity of the adenine band below 260 nm and the isoalloxazine band of flavin near 270 nm. Reproduced, with permission, from [99].

Table III. Standard Potentials of the Silver-Silver Chloride Electrode, at 25°, in Water-Dioxane Mixtures...

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