No abstract

The potential use of isosorbide, an original diol readily obtained by the double dehydration of sorbitol, has been investigated for the synthesis of novel amphiphilic species. The hydrophilicity of this polar head has been assessed via the synthesis and evaluation of three short-chain monoalkyl derivatives. The isosorbide polar head appears to have an unexpectedly low hydrophilicity, comparable to a diethylene oxide unit and it exhibits similar sensitivity to temperature changes. The monobutyl and monopentyl ethers of isosorbide have been found to be very efficient for the solubilisation of a model hydrophobic compound in water, giving promising hints on the use of isosorbide for the design of hydrotropic compounds.

The hydrotropic properties of short-chain monoalkyl ethers of isosorbide have been studied with emphasis on the difference between the two regioisomers (2-O- and 5-O-monoalkylisosorbide, C(i)Iso-exo and C(i)Iso-endo, respectively). On the one hand, the partitioning in a water/cyclohexane system has been measured, and on the other hand, the "optimal formulation" of C(i)Iso/oil/water systems has been determined by changing the oil polarity. In both cases, whatever the alkyl chain length (four or five carbons), C(i)Iso-exo appears to be less hydrophilic due to an intramolecular hydrogen bond that makes the free hydroxyl group less available. With one substituted position, the hydrophilicity contribution of isosorbide is slightly higher than the one of two ethylene glycols when the exo hydroxyl remains free, whereas it is closer to one ethylene glycol when this hydroxyl is substituted. With regard to the sensitivity to temperature, the hydrophilicity loss on heating seems to be similar for both isomers and close to what is obtained for poly(ethylene glycol) derivatives if we consider the evolution of the partition coefficients. In C(i)Iso-endo/oil/water systems, however, the variation of the optimal oil with temperature tends to show that the isosorbide derivatives are approximately 2 times less sensitive than their poly(ethylene glycol) counterparts to temperature changes.