Dimethylsulphoxide-water mixtures

In view of the diversity of medium effects between water and dimethylsulphoxide, we must expect any acidity function that is anchored to the pH scale in water to apply only to acids with very similar structures. Dolman and Stewart have reported values of the H acidity function in dimethylsulphoxide-water mixtures based on 24 substituted aniline and diphenylamine indicators. Dimethylsulphoxide containing 0.4 mol per cent water has a H value of 26.2. 

The use of ISEs in non-aqueous media(for a survey see [125,128]) is limited to electrodes with solid or glassy membranes. Even here there are further limitations connected with membrane material dissolution as a result of complexation by the solvent and damage to the membrane matrix or to the cement between the membrane and the electrode body. Silver halide electrodes have been used in methanol, ethanol, n-propanol, /so-propanol and other aliphatic alcohols, dimethylformamide, acetic acid and mixtures with water [40, 81, 121, 128]. The slope of the ISE potential dependence on the logarithm of the activity decreases with decreasing dielectric constant of the medium. With the fluoride ISE, the theoretical slope was found in ethanol-water mixtures [95] and in dimethylsulphoxide [23], and with PbS ISE in alcohols, their mixtures with water, dioxan and dimethylsulphoxide [134]. The standard Gibbs energies for the transfer of ions from water into these media were also determined [27, 30] using ISEs in non-aqueous media. 

An outstanding exception is the solvation of ions in dimethylsulphoxide (DMSO)-water mixtures. While in dimethylsulphoxide AG (Ag ) related to water is negative, in highly aqueous DMSO mixtures Ag is preferentially hydrated The change of preferential solvation of an ion with solvent composition has also been noticed for other ions This behavior can be attributed to the stabilization ... 

Cell (D) has been used several times to determine the solvent transference number A of the sparingly soluble salt Ag2S04 in the binary solvent mixtures acetonitrile-water l, dimethylsulphoxide-water and dimethylsulphoxide-methanol In Fig. 3 the solvent transference number of Ag2S04 is plotted versus Xdmso =... 

If a compound is poorly soluble in water, the pKa may be difficult to measure. One way around this problem is to measure the apparent pKa of the compound in solvent and water mixtures and then extrapolate the data back to a purely aqueous medium using a Yasuda-Shedlovsky plot. The organic solvents most frequently used are methanol, ethanol, propanol, dimethylsulphoxide (DMSO), dimethyl formamide (DMFA), acetone and tetrahydrofuran (THF). However, methanol is by far the most popular because its properties are closest to water. A validation study in water-methanol mixtures has been reported by Takacs-Novdk et al. (1997) and the determination of the pfCas of ibuprofen and quinine in a range of organic solvent-water mixtures has been reported by Avdeef et al. (1999). 

A 50% w/v solution of sodium hydroxide in water (12.5 ml, 0.32 mol) was added to a mechanically stirred suspension of diphenylacetonitrile (15.0 g,0.08 mol) and dibenzo-18-crown-6 (0.5 g, cat.) in dimethylsulphoxide (12.5 ml). The color rapidly deepened to an orange/brown. R-(-)-l-Dimethylamino-2-chloropropane (30.0 g, 0.095 mol) was added in portions over 30 min, this caused the temperature to rise to 30°C. After the addition was complete the mixture was warmed to 45°-50°C (water bath) and stirred for a further hour. The reaction mixture was then allowed to cool to room temperature and was poured into ice/water (250 ml) and extracted with ethyl acetate (3 times 150 ml). The combined extracts were dried (MgS04) and filtered and evaporated down to -100 ml. The product was extracted into IN HCI (100 ml+50 ml) and this was back washed with ethyl acetate. The aqueous was basified with 2 M sodium hydroxide and extracted into ethyl acetate (3 times 100 ml). The extracts were washed with brine (70 ml), dried (MgS04), and evaporated down to a yellow oil. This was chilled and triturated with cold hexane (50 ml) to give a white solid which was collected by filtration and washed thoroughly with a further portion of cold hexane (100 ml). 14.65 g (33%) of S-(+)-2,2-diphenyl-4-dimethylaminopentanenitrile were obtained, melting point 100°-101°C (recrystallised from hexane). 

TABLE 4. Transition state bond orders, n, and mixing entropy parameters, X, for the proton transfer between acetylacetone and RCOO in mixtures of dimethylsulphoxide and water. ... 

The next reaction for which we presented evidence in favour of mechanism is the aquation of pentaammine(dimethylsulphoxide)cobalt (III) perchlorate in water-organic solvent mixtures (non-aqueous components were dioxan, acetone, acetonitrile, methanol, ethanol, and n-propanol)(21). The D mechanism is represented by equations ( ) and (2), and the I mechanism by equation (3) (M = Co(NH2)5 ) ... 

Without presenting actual conductivities, Bhat and Manjunatha [188, 189] presented only the limiting conductances and the ion association constants of citric acid in water, in water + methanol, water + ethanol, water + acetonitrile and water + dimethylsulphoxide mixtures at 10, 20, 30 and 40 °C. Conductivity measurements of calcium ions in citrate buffers were performed by Davies and Hoyle [190, 191] and Wiley [192]. The citric acid interactions in acetonitrile were studied by Huyskens andLambeau [193,194]. 

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