Dimethylsulfoxide, hydrogen bonding, with

For example, according to Reichardt and references quoted by him (Reichardt 1988), the enol form of ethyl acetoacetate, CH3C(OH)=CHCOOC2H5, constitutes 65% of it in cyclohexane, 28% in toluene, 11.5% in acetone, and 5% in dimethylsulfoxide, due to competition between intra- and inter-molecular hydrogen bonding of the enol form. When such a competition is precluded, as in 5,5-dimethyl-l,3-cyclohexanedione, the opposite trend is observed there is 7% enol in toluene, 81% in acetone and 99% in dimethylsulfoxide (Reichardt 1988). In this case, the solvent with a higher electron pair donicity favours the hydrogenbonding enol form. 

Persistent interactions are not limited to hydrogen bonds. We mention for example those appearing in solutions of molecules with a terminal C=0 or C=N group dissolved in liquids such as acetone or dimethylsulfoxide. These solvents prefer at short distances an antiparallel orientation which changes at greater distances to a head-to-tail preferred orientation. The local antiparallel orientation is somewhat reinforced by the interaction with the terminal solute group and it is detected by the PCM calculation of nuclear shielding and vibrational properties. Recent experimental correlation studies [25] have confirmed the orientational behaviour of these solvents found in an indirect way from continuum calculations. The physical effect found in this class of solvent-solute pairs seems to be due to dispersion forces. 

Other Polymers. Other hydrophilic polymers also exhibit the shear stiffness anomaly when contacted with hydrogen bonding solvents. Films of amylose respond to water and dimethylsulfoxide as shown in Table III. When wet with water, there is a comparatively large increase in attenuation followed by a slow decline to a level plateau. We attribute this leveling out to the comparative water insolubility of retrograded amylose. Dimethyl sulfoxide is a much stronger solvent for amylose than is water and the increase in stiffness which is followed by a rapid decay to zero indicates complete film solution as was the case with water on PVA. The... 

Chemical fractionation of whole products and by-products from synthetic fuel production affords a logical first step in the evaluation of these materials for biological activity and the subsequent prediction of health hazards. Aliphatic and aromatic hydrocarbons, along with smaller amounts of heteroatomic species, constitute the bulk of all crude product materials and define a primary class separation need. Subfractionation of these fractions can lead to identification of bioactive components, Aliphatics are separated from the entire sample by a simple liquid chromatographic elution scheme. Aromatic compounds can be isolated by a cyclo-hexane-dimethylsulfoxide solvent partitioning scheme, A Sephadex LH-20 gel separation scheme appears feasible for the fractionation of crude liquids into aliphatic-aromatic, lipophilic-hydrophilic, polymeric, and hydrogen bonding classes of compounds. 

There are other polar solvents which are not protic. These involve liquids with large dipole moments. Some examples are acetonitrile, propylene carbonate, and dimethylsulfoxide. In each case, the solvent molecule possesses an electronegative group which is rich in electrons. The opposite end of the molecule is electron deficient but does not have acidic hydrogen atoms which can participate in hydrogen bonding. This class of solvents is called aprotic. 

The first Halex experiments have been carried out with neat chloroaromatics at high temperatures (400 - 500 °C) but the introduction of dipolar aprotic solvents in the late 50 s brought a dramatic improvement for the use of this process on a large scale under realistic conditions (0° < 200 - 250 °C) (ref. 4). It can be noticed that protic solvents, which decrease the nucleophilicity of the fluoride anion by strong hydrogen-bonding, are less adapted than aprotic ones. Commonly used dipolar aprotic solvents are dimethylsulfoxide (DMSO), tetramethylenesulfone (or... 

An analogous example is provided by the diaryl ureas, of which the parent molecule is 3. These are found to preferentially crystallize in homomeric fashion, i.e., with their own kind, as in 4, rather than forming cocrystals with guest molecules [99], This is true even for solutions containing strong hydrogen bond acceptors such as dimethylsulfoxide, which would be expected to interact with the amino hydrogens of... 

Contrary to expectations from the open tetrahedral hydrogen-bonded structure of ice, liquid water is a close-packed rather than an open liquid. It shares this property with 1,2-ethanediol, glycerol, and formamide, among common solvents, see Table 1.5. These four liquids have (1 — Vx/V) <0.1, whCTeas most otho" common solvents for ions have larger values of this quantity. Liquids that have large fractions of free volume, i.e., are open , are quite compressible, and there exists a moderate positive correlation of (1 — Vx /1 ) with the isothermal compressibility. Water shares a low isothermal compressibility, kj = 0.457 GPa at 25 °C, with the above named low-openness solvents for which kj < 0.5 GPa , whereas for other common solvents the values range from 0.524 (dimethylsulfoxide) to 1.706 (n-hexane) (Marcus 1998). 

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