Developing new green solvents is one of the key subjects in Green Chemistry. Ionic liquids (ILs) and deep eutectic solvents, thus, have been paid great attention to replace current harsh organic solvents and have been applied to many chemical processing such as extraction and synthesis. However, current ionic liquids and deep eutectic solvents have still limitations to be applied to a real chemical industry due to toxicity against human and environment and high cost of ILs and solid state of most deep eutectic solvents at room temperature. Recently we discovered that many plant abundant primary metabolites changed their state from solid to liquid when they were mixed in proper ratio. This finding made us hypothesize that natural deep eutectic solvents (NADES) play a role as alternative media to water in living organisms and tested a wide range of natural products, which resulted in discovery of over 100 NADES from nature. In order to prove deep eutectic feature the interaction between the molecules was investigated by nuclear magnetic resonance spectroscopy. All the tested NADES show clear hydrogen bonding between components. As next step physical properties of NADES such as water activity, density, viscosity, polarity and thermal properties were measured as well as the effect of water on the physical properties. In the last stage the novel NADES were applied to the solubilization of wide range of biomolecules such as non-water soluble bioactive natural products, gluten, starch, and DNA. In most cases the solubility of the biomolecules evaluated in this study was greatly higher than water. Based on the results the novel NADES may be expected as potential green solvents at room temperature in diverse fields of chemistry.

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Mixtures of solid chemicals may become liquid under certain conditions. These liquids are characterized by the formation of strong ionic (ionic liquids) or hydrogen bonds (deep eutectic solvents). Due to their extremely low vapor pressure, they are now widely used in polymer chemistry and synthetic organic chemistry, yet little attention has been paid to their use as extraction solvents of natural products. This review summarizes the preparation of ionic liquids and deep eutectic solvents with natural product components and recent progress in their applications to the extraction and analysis of natural products as well as the recovery of extracted compounds from their extracts. Additionally, various factors affecting extraction features of ionic liquids and deep eutectic solvents, as well as potential useful technologies including microwave and ultrasound to increase the extraction efficiency, are discussed.

Deep eutectic solvents (DESs) based on terpenes are identified and characterized. 507 combinations of solid components are tested, which results in the identification of 17 new hydrophobic DESs. Four criteria are introduced to assess the sustainability of these hydrophobic DESs from a chemical engineering point of view. These criteria include a viscosity smaller than 100 mPa•s, a density difference between DES and water of at least 50 kg•m −3 upon mixing of the DES and water, low transfer of the DES to the water phase and minor to no pH change. The results show that five new hydrophobic DESs based on natural components satisfy these criteria; thymol and coumarin (2:1), thymol and menthol (1:1), thymol and coumarin (1:1), thymol and menthol (1:2) and 1-tetradecanol and menthol (1:2), and thus are promising DESs. These new DESs can be considered as natural deep eutectic solvents, which have the potential to be environmentally friendly. A selected group of the hydrophobic DESs were used for the extraction of riboflavin from water. They all show higher removal of riboflavin in comparison to decanoic acid:tetraoctylammonium bromide (2:1). The highest extraction efficiency of riboflavin from water, 81.1%, was achieved with the hydrophobic DES DecA:Lid (2:1).

The phase behavior of the binary system consisting of the supercritical fluid carbon dioxide (CO2) and the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) was studied experimentally. A synthetic method was used to measure its phase behavior. Bubble-point pressures of the system CO2 + [bmim][BF4] are reported for carbon dioxide concentrations ranging from (10.22 to 60.17) mole % and within a temperature range of (278.47 to 368.22) K. The CO2 + [bmim][BF4] binary system has a two-phase liquid−vapor region extending up to very high pressures. Most likely, the type of fluid-phase behavior is type III according to the classification of Scott and Van Konynenburg. The experimental results obtained were compared with the available phase behavior data of the binary system CO2 + 1-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4]) to investigate the effect of the length of the alkyl group on the phase behavior of this type of system. A larger alkyl group leads to lower bubble-point pressures and, therefore, to higher solubilities of carbon dioxide in the imidazolium-based ionic liquid.

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Development of a water-free dyeing process for cotton is essential for the textile industry due to ecological and economical reasons. In this study, a dyeing method is described where cotton has been effectively dyed in supercritical carbon dioxide (scCO 2 ). Excellent dye fixation of 100%, and colour strength (K/S) values up to 30, were achieved in a small batch reactor and in a scale-up vessel. A series of non-polar reactive dyes with fluorotriazine as reactive group were synthesised at our laboratory. Fluorotriazines were found to be the best dyes for dyeing cotton and their reaction with cotton was improved by adding small quantities of acids to the reaction medium. H 3 PO 4 and HAc were tested at different concentrations on cotton dyed with fluorotriazines. Evenly dyed pieces of cotton without any damage to the cotton fibres were observed in all experiments. An important step forward has been made for the future commercialization of a green process for industrially dying cotton in scCO 2 . Elimination of water and its costly treatment can be now achieved in the cotton dyeing process.