Solubilization in Nonaqueous Solvents

In micellar solutions of ionic surfactants the mechanism for solubilization of the small polar molecules appears to involve, initially at least, ion-dipole interaction between the solubilizate and the counterion of the surfactant present in the interior of the micelle, possibly followed by weaker interaction (e.g., via hydrogen bonding) between the solubilizate and the surfactant ion (Kaufman, 1964 Kitahara, 1969, Kon-no, 1971a). In solutions of nonionic POE surfactants, solubilization of polar molecules appears to be by interaction with the ether oxygens of the POE chain. 

A classification of solubilization isotherms for small polar molecules into nonaqueous solvents by surfactants, based on the strength of interaction between solubilizate and surfactant, has been proposed by Kon-no and Kitahara (Kon-no, 1972a). When the moles of material solubilized per mole of surfactant are plotted against the relative vapor pressure, p/p°, of the system at constant temperature (where p is the vapor pressure of the water in the system and p is the vapor pressure of pure water), isotherms are obtained whose shapes reflect the strength of the solubilizate-surfactant interaction. Systems having strong surfactant-solubilizate interaction are concave to the plp° axis, whereas those showing weak interaction are convex to that axis. Systems with very weak solubilizate-surfactant interaction show almost linear isotherms. 

The maximum amount of water solubilized into hydrocarbon solvents by ionic surfactants appears to increase with increase in the concentration of the surfactant, the valence of the counterion, and the length of the alkyl chain (Kon-no, 1971b) and with the introduction of double bonds into the hydrophobic group (Demchenko, 1971). Straight-chain compounds appear to solubilize less water than branched-chain ones, possibly because the former form micelles that are more compact and rigid than the latter (Frank, 1969 Kon-no, 1971c). 

Change in the nature and molecular weight of the solvent affects the extent of solubilization of water. The amount solubilized by sodium di(2-ethylhexyl)sulfo- 

From the data available for surfactants with similar hydrophobic groups, the solubilizing power for water into hydrocarbon solvents appears to decrease in the following order anionics nonionics cationics (Kon-no, 1971c). 

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The versatility of permanganate as an oxidant has been greatly enhanced in the past decade by the observation that it can be solubilized in nonaqueous solvents with the aid of phase transfer agents (1). The literature contains descriptions for the use of this procedure for the oxidation of alkenes (2-13), alkynes (13-18), aldehydes (19), alcohols (20), phenols (21,22), ethers (23), sulfides (24,25), and amines (20,26). The dehydrogenation of triazolines has also been achieved by the use of permanganate and a phase transfer agent (27). ... 

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