Solvent reversibility

The majority of practical micellar systems of Tionnal micelles use water as tire main solvent. Reverse micelles use water immiscible organic solvents, altlrough tire cores of reverse micelles are usually hydrated and may contain considerable quantities of water. Polar solvents such as glycerol, etlrylene glycol, fonnamide and hydrazine are now being used instead of water to support regular micelles [10]. Critical fluids such as critical carbon dioxide are... 

Reverse Osmosis and Ultrafiltration. Reverse osmosis (qv) (or hyperfiltration) and ultrafilttation (qv) ate pressure driven membrane processes that have become well estabUshed ia pollution control (89—94). There is no sharp distinction between the two both processes remove solutes from solution. Whereas ultrafiltration usually implies the separation of macromolecules from relatively low molecular-weight solvent, reverse osmosis normally refers to the separation of the solute and solvent molecules within the same order of magnitude in molecular weight (95) (see also Membrane technology). 

When carboxylate salts are put into nonpolar solvents, reversed micelles often are formed, where the polar parts of the molecules are on the inside and the nonpolar parts are on the outside. 

An additional study revealed similar agglomeration behavior when the batch in DMF was charged into the antisoivent IP AC solvent (reverse addition). As shown in Fig. 9-21, PSD data revealed distinct shoulders from 10 to 100 pm for reverse addition operation. Again, this result corroborated the criticality of local mixing for the reverse addition operation. Oil droplets were also observed during this mode of addition. 

Methylation and benzylation of the pyrrolidine dienamine of 3-methyl-A "-2-octa-lone gives a mixture of N- and jS-alkylated products in protic and aprotic solvents. However, the position of attack by acrylonitrile and methyl acrylate is solvent-dependent. In protic solvents the / -alkylated octalone is obtained on hydrolysis, whereas in aprotic solvents the -alkylated product is produced (Scheme 7). This change in the regioselectivity arises from the C-3 methyl group being forced into a quasi-axial orientation because of allylic strain in the equatorial orientation. As a consequence the carbanionic centre in the initially formed zwitterion 6 cannot be neutralized by an internal proton transfer of an axial proton at C-3. In protic solvents intermolecular protonation renders the reaction irreversible, but in aprotic solvent reversion to starting material occurs. This allows 5- or -alkylation to occur and this is rendered irreversible by internal proton transfer from the 6 - or 5-position, respectively, to the carbanionic centre in the resulting zwitterion (Scheme 7). 

Reverse micelles have an inverted structure in comparison to the conventional normal micelles in aqueous systems. Therefore, they are often known as inverse or inverted micelles. In reverse micelles, the micellar cores consist of a hydrophilic polar component and the shells consist of lipophilic nonpolar part of the surfactant molecules. The dipole-dipole interaction between the hydrophilic headgroups acts as one of the driving forces for the formation of reverse micelles in organic solvents. Reverse micelles are mostly observed in the ternary mixtures of surfactant/ water/oil, mostly in oil-rich regions [1-3]. Furthermore, reverse micelles have also been observed in aqueous systems of UpophUic surfactant in surfactant-rich regions [4, 5]. In most of the studies carried out in the past, water was regarded as an essential component in the formulation of reverse micelles. Only a few reports exist in the literature of surfactant science that describe the formation of reverse micelles in organic solvents without water addition [6-10]. 

This phenomenon, called reverse osmosis, is used in a number of processes. An important commercial use is in the desalination of seawater or brackish water to produce fresh water. Unlike distillation and freezing processes used to remove solvents, reverse osmosis can operate at ambient temperature without phase change. This process is quite useful for processing of thermally and chemically unstable products. Applications include concentration of fruit juices and milk, recovery of protein and sugar from cheese whey, and concentration of enzymes. 

Molybdenum alkoxides, Mo2(OR)e, react in hydrocarbon solvents reversibly with two moles of CO2 to yield the corresponding bis (alkyl carbonates) (Eq. 2.285). ... 

Russell A E, Shuttleworth S G, Williams-Wynn D A 1967 Further studies on the mechanism of vegetable tannage. Part III. Solvent reversibility of wattle tannage. J Soc Leather Trades Chem 51(10) 349-361... 

The evolution of the two-phase system may, however, be more complex. Solubilization of some hydrocarbons in the micellar aqueous phase can take place. Surfactant molecules can migrate across the water-liquid hydrocarbon interface and form structures that have been called reversed micelles, providing the surfactant concentration in the whole system is high enough to reach the critical aggregation concentration in the considered hydrocarbon solvent. Reversed micelles have an aqueous core ensuring the hydration of hydrophilic head group, whereas hydrophobic tails orient toward the nonpolar liquid. It is not our purpose to discuss surfactant behavior in nonaqueous media. 

If a mixture of tetrahydrofuran and tetramethylethylenediamine (TMEDA) is used, predominantly (97 3) the meta product 40 is obtained. In contrast, using diethyl ether as a solvent reverses the selectivity in favor of the ortho product 39, albeit with somewhat lower selectivities (78 22). 

There are several synthetic methods to produce this representative superabsorbent polymer (SAP). In general ttiey are (1) an aqueous solution polymerization method in which organic solvents are not used and (2) a suspension polymerization method in which the aqueous solution of a monomer is suspended in an organic solvent (reverse phase suspension polymerization). 

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