Volatile short-chain amphiphiles derived from isosorbide: Hydrotropic properties of esters vs. ethers

Two series of short-chain isosorbide monoalkanoates, differing from the free hydroxyl position, were synthesized and evaluated as volatile non-ionic hydrotropes, also known as solvo-surfactants''. Their aqueous solubilities, solubilizing efficiencies and volatilities were evaluated and compared to the corresponding 5-O-alkylisosorbides. Whatever the acylation position (5-O- or 2-O-), isosorbide monoalkanoates are poorly water-soluble for acyl chains longer than four carbons, whereas 5-O-alkylisosorbides are completely miscible with water up to a pentyl chain, which seems to indicate that an ether link brings more hydrophilicity than an ester bond for these types of molecules. The shorter isosorbide monoalkanoates are completely miscible with water and the butanoates are particularly efficient in terms of aqueous solubilization of hydrophobic compounds. In addition, all hydrotropes exhibit some volatility albeit being non-VOC and contrarily to their ethers homologues, isosorbide alkanoates are easily hydrolysed in basic medium, which suggests a good biodegradability.