Hydrotropic properties of alkyl and aryl glycerol monoethers.

Three pentyl and three aryl 1-O-monoglyceryl ethers prepared via a green catalytic route were investigated as hydrotropic solvents. Their amphiphilicities were quantified by comparing their so-called "fish" diagrams constructed with oils of increasing hydrophobicity (EACN). For the same number of carbon atoms, the presence of a methyl substituent in β position makes the hydrotrope slightly more hydrophobic, as evidenced by the more hydrophobic optimal oil. Branched isomers are also less efficient since they require higher concentrations to get microemulsions. The presence of an aromatic moiety within the hydrophobic chain increases the solubility of the hydrotrope in water in comparison to the alkyl derivative that has the same number of carbon atoms. It also modifies significantly the associative behavior in oil/water systems: Benzylglycerol monoether is able to form Winsor III systems, just as the pentyl derivatives, but with much more polar oils, whereas phenylglycerol is not. In oil/water systems, all glycerol-derived amphiphiles exhibit a twice-lower temperature-sensitivity compared to their ethyleneglycol counterparts. The pentyl and benzyl 1-O-monoglyceryl ethers can be classified as amphiphilic solvents, or "solvo-surfactants", as regards to their surface-active properties and good solubilizing abilities.