Acetone-water solvent

In addition to the reactions discussed above, there are still other alkyne reactions carried out in aqueous media. Examples include the Pseudomonas cepacia lipase-catalyzed hydrolysis of propargylic acetate in an acetone-water solvent system,137 the ruthenium-catalyzed cycloisomerization-oxidation of propargyl alcohols in DMF-water,138 an intramolecular allylindination of terminal alkyne in THF-water,139 and alkyne polymerization catalyzed by late-transition metals.140... 

A typical isolation strategy is the preliminary purification of the n-butanol extract over dextran supports like Sephadex LH20 or Fractogel TSK, followed by further fractionation of the crude saponin mixtures [111]. A new generation of polymers has been exploited for the initial purification steps. They are highly porous polymers (Daion HP-20, MCI gel CHP-20P (both from Mitsubishi Chemical Industries, Tokyo), Amberlite XAD-2) [112], Methanol-water or acetone-water solvent gradients are used. 

Of particular interest are asymmetric dihydroxylation (AD) reactions. Depending on the oxidant employed, which is commonly either NMO or K3[Fe(CN)6]/K2C03, two different mechanisms may apply (see Schemes 5.12 and 5.13).[701 One essential difference is that A-morpholinc-A -oxide is typically used in a homogeneous acetone-water solvent mixture while a biphasic reaction mixture is usually observed with aqueous K3[Fe(CN)6 /K.2C03 as oxidant. In the latter case the olefin is oxidised... 

Figures 11-14 to 11-17 show the differential scanning calorimetry (DSC) thermograph of the acetone/ water solvent mixture with and without the presence of imipenem. The DSC curves indicate endothermic peaks which correspond to the phase transitions. The peaks around O C and —95°C represent the melting of the solid water and acetone phases, respectively. The peaks around — 19°C represent the melting of the solid clathrate phase (Rosso et al. 1975). The clathrate is a solid phase complex of 17 water molecules surrounding a single molecule of acetone, niLDOCllOrCO. In addition, the DSC thermograms indicate only slight temperature flucUiations for the endotherms with the addition of imipenem and the sodium bicarbonate. Therefore, the acetone/water binary phase behavior is not affected significantly by the addition of imipenem and sodium bicarbonate.

Higher yields, almost quantitative, are reported when the solvent DMSO is used either in combination or without ion-exchange resins [23-27]. But from the ecological point of view the use of DMSO is unfavorable and furthermore the separation of the solvent DMSO from the desired product HMF is difficult. A different solvent approach utilizing a solvent with higher volatility and thus easier separation from HMF is the use of a sub- and supercritical organic solvent like acetone. In a 9 1 mixture of acetone/water - water is needed due to the low solubility of D-fructose in pure acetone - and sulfuric acid catalysis at a temperature of 180°C and a pressure of 20 MPa, high fructose conversion and HMF selectivity (up to 77%) could be achieved without the formation of insoluble humic acids [28-31]. The tremendous increase in selectivity for the acetone/water solvent system could be... 

Figure 9.11 Scanning electron micrographs of slow drying (stagnant air) versus fast drying (impinging jet of air) coatings of cellulose acetate in mixed acetone-water solvent...

The aquation kinetics of [Co(NH3)5Cl] and [Co(NH3)5Br] have been studied using acetone-water solvent over a wide range of solvent compositions and temperatures in an attempt to correlate the rate constant with the dielectric constant of the medium.The variation of thermodynamic properties of the activated complex with the mole fraction of acetone reveals the existence of specific solvation. 

The universal solvent for cellulose acetate is acetone. Spinning dopes are prepared by dissolving the flake in an acetone-water solvent composition of about 95/5. The small amount of water significantly reduces the viscosity of a concentrated solution of cellulose acetate such as for a 25% solution. Other solvents for cellulose acetate are ethyl methyl ketone, dioxane, pyridine, nitroethane, dimethylformamide, dimethylacetamide, formic acid, and acetic acid. Although methylene chloride alone is not a good solvent for cellulose acetate, 9/1 methylene chloride-methanol is a good solvent. 

Fluorescence studies of volume phase transition of polyacrylamide (PAAM) in mixed acetone/ water solvent, with incorporated dansyl group and pyrenyl probe were reported by Hu and co-workers [70, 71]. They observed an increase in the fluorescence lifetime of the probe with increase of acetone content in the solvent. They reported that gradual increase of fluorescence lifetime accompanies the volume phase transition of the PAAM gels from the swollen to collapsed state with increasing hydrophobicity of the microenvironment. 

We believe that the presence of free H in the acetone/water solvent system plays a role in the monocationic system. The rate determining step, once again, is the reductive elimination of aldehyde with a calculated barrier of 21.6 kcal (Fig. 14). Protonation of the monocationic dirhodium acyl is an alternate and likely pathway for eliminating aldehyde and forming the dicationic dirhodium catalyst Hr. Due to the very low activation barrier for the monocationic aUcyl-CO migratory insertion step, protonation of Rh-alkyl species to produce alkane is far less likely and consistent with the much lower alkane side reactions for 15r. 

In hexane and 10% acetone water solvents, ozone readily oxidized aldrin to dieldrin (Hoffman and Eichelsdoerfer, 1971). 

The introduction of polar groups such as carboxylic acid groups modified polymer physical properties. As reported in Table 4, PHOioo-xUx samples are soluble in organic solvents such as dichloromethane, chloroform, tetrahydrofuran, but are insoluble in polar solvents such as methanol, acetone/water 85/15 (v/v). After oxidation PHO90U10 and PH09oDio(cooh) behaved differently in acetone/water solvent. More clearly, contrary to PHO75U25, PH075D25(cooh) was soluble in methanol, acetone, and in different acetone/water mixtures. 

The quest for additional conformational information has led to the investigation of hydroxyl protons in aqueous solution. Samples are dissolved in mixed methanol-water or acetone-water solvents, and analysed in capillary NMR tubes at low (-5 to -15°C) temperatures. Chemical exchange of hydroxyl protons is reduced to the point that it is possible to use them as probes of hydration and hydrogen bonding. Distance information can also be extracted from NOESY or ROESY spectra under these conditions. 

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