ORIGINAL ARTICLE Solubilizing and Hydrotropic Properties of Isosorbide Monoalkyl- and Dimethyl-Ethers Morgan Durand Æ Ying Zhu Æ Vale ´rie Molinier Æ Thierry Fe ´ron Æ Jean-Marie Aubry Received: 18 November 2008 / Accepted: 10 February 2009 / Published online: 19 May 2009 Ó AOCS 2009 Abstract Isosorbide is a diol readily obtained from starch that can be used as a polar building block for the synthesis of derivatives ranging from solvents to surfactants: dime- thyl isosorbide (DMI) is a ‘‘sustainable solvent’’ already on the market, used notably in cosmetic and pharmaceutical formulations; monoalkyl derivatives of isosorbide are non- ionic hydrotropes that could be potential substitutes to short-chain glycol ethers. The use of these isosorbide derivatives as bio-sourced alternatives to petroleum- derived products for applications such as compatibilizers in liquid detergent formulations or solubilizing agents in aqueous hard-surface cleaning is discussed in this paper. DMI reveals to have interesting coupling properties for the former applications, whereas the monopentyl ether of iso- sorbide (C 5 Iso) is a particularly efficient hydrotrope for the latter. Keywords Isosorbide  Dimethyl isosorbide  Sorbitol  Solvent  Co-solvent  Hydrotrope  Solubilization Introduction Hydrotropes are usually referred to as small molecules able to greatly enhance the aqueous solubility of a wide variety of organic compounds, as for instance perfumes, dyes, active ingredients or fatty soils. They find applications in many industrial fields [1]. In addition to this solubilizing action, hydrotropes exhibit properties of the so-called ‘‘coupling agents’’, i.e. they are able to increase the cloud point of non-ionic surfactant systems, thus allowing to get a clear solution at the temperature of use, and they also hinder the formation of gels by destabilizing surfactant liquid crystal assemblies [2]. Both the solubilizing and coupling actions of hydro- tropes are of great interest in the formulation of liquid detergents or liquid household cleaners [1, 3]. Liquids are often preferred to powdered products, because they are easy to use, as neat or diluted, dissolve rapidly in water, and can also incorporate in their formulation sensitive ingredients that could not suffer the drying processes in the manufacture of dry powders. Liquid detergents usually contain high amounts of surfactants (30–50% weight) [4], which makes it difficult to get a clear and stable formula- tion, and can also lead to thick and uneasy-to-pour prod- ucts. The addition of coupling agents, allowing to obtain a clear, homogeneous and low-viscosity solution, is often required. A wide range of molecular structures can lead to hydrotropic behavior [5–7]. Usual hydrotropes present a weak amphiphilic character, with small hydrophilic and hydrophobic moieties. They can be, among others, aro- matic salts (sodium xylene sulfonate SXS), aromatic alcohols (pyrogallol) or short-chain soaps (sodium n-pentanoate). Medium and short-chain alkylpolyglucosides (APG) have also been regarded as hydrotropes [8], as well as more unusual compounds such as long chain dicarboxylic acids [9]. Short-chain amphiphiles derived from ethylene glycol (C i E j ), propylene glycol (C i P j ) or glycerol (C i Gly 1 )[10] also present hydrotropic properties. These compounds are sometimes called ‘‘solvo-surfactants’’ because they M. Durand  Y. Zhu  V. Molinier (&)  J.-M. Aubry LCOM, Equipe ‘‘Oxydation et Physico-Chimie de la Formulation’’, UMR CNRS 8009, ENSCL BP 108, 59652 Villeneuve d’Ascq Cedex, France e-mail: valerie.molinier@univ-lille1.fr T. Fe ´ron Roquette Fre `res, 62080 Lestrem, France 123 J Surfact Deterg (2009) 12:371–378 DOI 10.1007/s11743-009-1128-4