DMSO-water binary mixture solvents

Reaction kinetics and mechanisms for oxidation of [Fe(diimine)2(CN)2], [Fe(diimine)(CN)4] (diimine = bipy or phen) (and indeed [Fe(CN)6] ) by peroxoanions such as (S20g, HSOs", P20g ) have been reviewed. Reactivity trends have been established, and initial state— transition state analyses carried out, for peroxodisulfate oxidation of [Fe(bipy)2(CN)2], [Fe(bipy)(CN)4] , and [Fe(Me2bsb)(CN)4] in DMSO—water mixtures. Whereas in base hydrolysis of iron(II)-diimine complexes reactivity trends in binary aqueous solvent mixtures are generally determined by hydroxide solvation, in these peroxodisulfate oxidations solvation changes for both partners affect the observed pattern. ... 

Figure 16.5. Snapshots of flie simulation of different binary mixtures - water-DMSO in the top panel, water-eflianol in die middle, and water-TBA in the bottom panel. Water moleeules are shown in silver. Co-solvents (DMSO, edianol, and TBA) are represented in blue. The snapshot is shown at two different coneentrations - one before the onset of percolation to show the microheterogeneity in the system, and one after the onset of percolation to show the spanning cluster of the cosolvent. Figure adapted with permission from J. Phys. Chem. B, 115 (2011), 685. Copyright (2011) American Chemical Society.

The diffusion coefficients of ionic solutes show nonideal behavior with variation of composition of the solvent mixture in water-methanol binary mixtures. The degree of non-ideality of the solute diffusion is found to be similar to the nonideality that is observed for the diffusion of water and methanol molecules in these mixtures and is attributed to the enhanced stability of the HBs and formation of interspecies complexes in the mixtures. The diffusion coefficient of water is found to be minimum at 0-5 and that of methanol shows the minimum at = 0.7. However, the observed deviation from linear behavior with composition is found to be a bit weaker than that found in simulations of water-DMSO mixtures [11,12],... 

Interestingly, mostly those aqueous binary mixtures that contain a marked amphiphilic character towards water are found to be particularly important in chemistry and biology. This is clearly manifest in all useful aqueous binary mixtures such as DMSO, methanol, ethanol, TBA, acetone, and dioxane to name a few. Some of these solvents (DMSO, EtOH) are used at high concentration as effective denatur-ants of protein. At low concentration they can exhibit a reversal of role and serve as a promoter of stability. In this low-concentration regime the binary mixtures also promote the catalytic activity of enzymes, as discussed above. Recent experimental, theoretical, and simulation results exhibit the phase-transihon-hke scenarios discussed in this chapter. These systems need to be studied in great detail as much remains to be understood. 

Catalan, J., Diaz, C., and Garcia-Bianco, F. 2001. Characterization of binary solvent mixtures of DMSO with water and other cosolvents. J. Org. Chem. 66, 5846-5852. 

HP he study of the behavior of electrolytes in mixed solvents is currently arousing considerable interest because of its practical and fundamental implications (1). Among the simpler binary solvent mixtures, those where water is one component are obviously of primary importance. We have recently compared the effects of small quantities of water on the thermodynamic properties of selected 1 1 electrolytes in sulfolane, acetonitrile, propylene carbonate, and dimethylsulfoxide (DMSO). These four compounds belong to the dipolar aprotic (DPA) class of solvents that has received a great deal of attention (2) because of their wide use as media for physical separations and chemical and electrochemical reactions. We interpreted our vapor pressure, calorimetry, and NMR results in terms of preferential solvation of small cations and anions by water and obtained... 

From the above and similar investigations [Mo 71, Be 73], it could be seen that, in various binary solvent mixtures containing water, acetonitrile, methanol and dimethyl sulphoxide, the solvating effects of the individual components are generally proportional to the effects displayed by the pure solvents. An exception is the H2O-DMSO mixture, in which the silver ion occurs only in the forms of its pure aquo complex and its pure DMSO complex. 

The acetone-methanol binary homogeneous minimum-boiling azeotropic system is considered with some of the solvents studied by Kossack et al. Three solvents are explored that have different normal boiling points (373 K for water, 464 K for DMSO, and 405 K for chlorobenzene). These solvents have different effects on the azeotropic mixture. The first and second solvents drive the acetone overhead in the extractive column. The chlorobenzene solvent drives the methanol overhead in the extractive column. The normal boiling points of acetone and methanol are 329 and 338 K, respectively, so acetone is the lighter component and would preferentially go overhead. The composition of the acetone-methanol azeotrope is 77.6 mol% acetone at atmospheric pressure as shown in Figure 11.1. 

One type of solvent-effect study considers diverse solvents such as water, methanol, acetonitrile, toluene, dimethyl sulfoxide (DMSO), and so on. These studies showed a variation in the alpha effect but, as may have been expected, did not point to a single factor such as solvent polarity as causing the rate enhancement. Interestingly, it was the variation in solvent composition of binary solvent mixtures, such as DMSO-H O and MeCN-HjO, that gave the most valuable clues concerning the origin of this solvent effect of alpha nucleophiles. 

Miscellaneous kinetic studies of solvolysis in binary aqueous mixtures have included those of the [Co(NH3)5(dmso)] + cation in seventy-one such mixtures, of the /rans-[Co(dmgH)2Cl(N02)] anion and its methylglyoximate analogue in ethanol- and propan-2-ol-water, of [Cr(sal)3] and of ajffy5-tetra-(p-sulphonato-phenyl)porphineiron(m) in ethanol-water, of the 5,6-dimethylbenzimidazoIe derivative of methylcobalamin, of the acid-catalysed hydrolysis of (BHJ- in acetonitrile containing small amounts of water, and of the rate-determining aquation prior to redox of the [Mn(ox)2(OH2)a] anion in aqueous dimethylformamide. A kinetic study of the reaction of thallium(m) with dimethylformamide indicates caution in the use of this co-solvent in binary aqueous mixtures at elevated temperatures or in the presence of oxidants. ... 

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