Glucose-based deep eutectic solvents: Physical properties Adeeb Hayyan a, b , Farouq S. Mjalli a, ⁎, Inas M. AlNashef c , Yahya M. Al-Wahaibi a , Talal Al-Wahaibi a , Mohd Ali Hashim b a Petroleum and Chemical Engineering Department, Sultan Qaboos University, Muscat 123, Sultanate of Oman b Department of Chemical Engineering, Centre for Ionic Liquids (UMCiL), University of Malaya, Kuala Lumpur 50603, Malaysia c Chemical Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia abstract article info Article history: Received 15 April 2012 Received in revised form 22 November 2012 Accepted 23 November 2012 Available online 10 December 2012 Keywords: Glucose Monosaccharides Deep eutectic solvents Ionic liquids Deep eutectic solvents (DESs) are considered nowadays as green ionic liquid (IL) analogues. Despite their rel- atively short period of introduction as a special class of ILs, they have been under an increasing emphasis by the scientific community due to their favorable properties. In the present study, a glucose based DES of cho- line chloride (2-hydroxyethyl-trimethylammonium chloride) with the monosaccharide sugar D-glucose an- hydrous was synthesized at different molar ratios. The physical properties of density, viscosity, surface tension, refractive index, and pH were measured and analyzed as function of temperature in the practical temperature range of 298.15–358.15 K. The analysis of these physical properties revealed that these novel DESs have the potential to be utilized for several possible industrial applications involving processing and separation of food constituents, pharmaceutical applications, as well as mediums for chemical reactions. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Ionic liquids (ILs) have received escalating attention in organic synthesis, due to their unique physicochemical properties and their availability compared with conventional solvents. ILs have many favorable merits that distinguish them from conventional solvents. Not to mention all, ILs are known to have undetectable vapor pres- sure, wide liquid temperature range, special solubility for many organic or inorganic compounds, and less toxicity[1–3]. ILs have been used in many chemical applications such as CO 2 capture [4], battery development [5], electrochemical applications [6] and bio- logical applications such as biocatalysis [7]. ILs can be applied in many chemical and industrial processes [8]. Recently, ILs were ap- plied in the separation of food constituents such as separation of sugars from natural fruits [9]. This is due to the fact that their physi- cal and chemical properties can be tailored by the judicious selection of their basic building block (cation, anion and substituent) [9]. Deep eutectic solvents (DESs) are relatively new class of ionic liquids that can be simply synthesized via mixing of a salt with a hydrogen bond donor compound. A common example is the DES between choline chloride and urea [10,2]. Due to their favorable properties, DESs were reported in many industrial applications as attractive alternatives to ILs. DESs share with ILs many of their intrinsic merits such as their bio- degradable components, non-flammability due to their low or none measurable vapor pressure, and low toxicity [1,2,11]. Additionally, DESs are much cheaper than ILs which makes them readily available for large scale industrial applications. DESs were introduced in many applications and product preparations. Examples of such are in the syn- thesis of zeolite analogues [12], liquid–liquid extraction for aromatic separation from naphtha [13], mediums for the deposition of specific metals in the electro and electroless plating of metals [14,15] and in the removal of excess glycerol from biodiesel fuel [16]. Moreover, it was found that DES can be used as template-delivery agents in a con- trolled manner for the synthesis of materials [17]. The sugar industry sector is a very promising field which contributes much to the food and pharmaceutical industry. Research and develop- ment in the field of sugar separation and fractionation from natural bio-resource materials such as local fruits are necessary to improve the sugar industry and utilize the abundant bio-resource. Conventional sugar separation and fractionation technologies are expensive, compli- cated and sometimes not suitable to deal with sensitive food ingredi- ents. There exists a great need for improving these technologies and introducing new separation methods. The key concept that contributes in this direction is the adoption of green engineering methodologies which improve the sustainability, efficiency, biodegradability, and envi- ronmental friendliness [2,18–20]. Recently, AlNashef et al. [9] patented a novel process for the separation of sugars from mixtures of fructose and glucose from a liquid phase or a solid mixture containing the fruc- tose and glucose using ionic liquids. The patent claimed that ionic liquids work as selective agents that can separate glucose and fructose under ambient conditions. For example solubility of 1,3-dimethylimidazolium dimethylphosphate is 2–6 times higher than that of fructose [9]. The next step in improving this technology is by reducing its cost to make it practically available for industrial scale applications. DESs can contribute much in this area. These new and environmental friendly Journal of Molecular Liquids 178 (2013) 137–141 ⁎ Corresponding author. Tel.: +968 2414298 1558; fax: +968 24141354. E-mail address: farouqsm@yahoo.com (F.S. Mjalli). 0167-7322/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molliq.2012.11.025 Contents lists available at SciVerse ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq