WO2024194599A1 - Ionic liquids - Google Patents

Abstract

The application relates to an ionic liquid comprising a polyetherdiamine carboxylate or a polyethertriamine carboxylate.

Description

Ionic Liquids The invention relates to ionic liquids comprising a polyetherdiamine carboxylate or a polyethertriamine carboxylate, to methods of producing such ionic liquids and to uses and methods of using such ionic liquids. Solvents are important in most efficient chemical reactions and the chemistry of organic, bioorganic and inorganic chemistry.^1-3 They are often essential to carry out a successful chemical reaction.¹ Volatile organic compounds (VOCs) are commonly used in both laboratory and industrial processes with many advantageous properties, such as the ability to be easily separated from the reaction medium.² However, the use of VOCs in unsustainable in that they harm our environment due to intrinsic volatility and often toxicity. It is well documented and accepted that long-term exposure to VOCs may harm the liver, kidneys and other vital organs as well as damage the atmosphere and land. VOCs evaporate under ambient conditions resulting into transfer to the environment and atmosphere producing undesirable photochemical ozone smog which can be harmful and carcinogenic.⁴ The use of non-volatile ionic liquids as solvents and reagents has expanded in recent years being recognised as more sustainable with a significant reduction in waste and pollution at both laboratory and industrial scales⁵. Solvents can typically make up to 70 to 80 percent of the process medium.² Alternative liquids as solvents have been considered “green” with a reduced/low environmental impact during their full life cycle helping to solve environmental issues while also contributing to overall process optimisation.^{6, 7} There are five main categories, ionic liquids (ILs), deep eutectic, and thermomorphic, fluorous solvent and supercritical fluids.² ILs are amongst the most promising candidates for resolving some of our major challenges with regards to chemical pollution. Ionic liquids are considered as a clean, efficient, and environmentally friendly alternative to VOCs, and can offer other substantial benefits due to their unique thermal, physical and biological capabilities. ILs are sometimes called designer solvents as their properties can be tuned by changing the combination of cations and anions to fit a specific use.^{2, 8} They have characteristics that adhere to some of the 12 principles of green chemistry. The term environmental factor (E-factor) is a metric to assess how “green” a particular reaction is in terms of waste. The closer to zero the E-factor is, the better. In the case of ILs, E-factor values tend to be near or equal to zero.^{2, 9, 10} ILs are “molten salts” that are typically liquid at temperatures below 100 °C and even at ambient temperature.^{2, 11} Common ILs are a mixture of organic cations, quite often N derivatives or N’-substituted imidazolium, with organic or inorganic anions (i.e. HSO4-).^{8, 12} Strong electrostatic interactions between ions provide chemical and thermal stability, excellent solubility in organic and inorganic substances of various polarities, as well as low flammability and insignificant vapour pressure in temperatures below 400 °C.^{1, 13} They can provide highly viscous solvents in specific chemical reactions.² In order to generate reliable data for chemical and physical analyses, analytical grade ILs are required.^{8, 14} Other advantages of ILs include reduced waste production, easy solvent recovery and low environmental emissions.¹⁵ As a result, the use of ILs has expanded in a variety of sectors, including battery technology,¹⁶ medicine¹⁷ and solar cells.¹⁸ For example, tetraethylammonium tetrafluoroborate (Et4N⁺BF4-) in acetonitrile (ACN) is wildly utilised in various applications, including supercapacitors, as a background electrolyte in cyclic voltammetry due to a low viscosity leading to high conductivities. However, it is flammable, very volatile and non-renewable, resulting in environmental pollution.^{19, 20} ILs have shown excellent performance in clean energy generation reactions, particularly as electrolytes for hydrogen synthesis via water electrolysis.^{21, 22} They have grown in popularity due to their superior thermal stability, low volatility, and fire-retardant properties when compared to organic solvent-based electrolytes.^{1, 23} There are two main types of ILs: aprotic ILs (APILs) and protic ILs (PILs) ²⁴. Normally, proton transfer from a Brønsted acid to a Brønsted base produces PILs.²⁵ These can be inexpensive and easy to synthesise as their synthesis does not result in the formation of by-products.²⁶ Thermal stability of a PIL is important for use²⁷ with PILs containing a bis(trifluoromethane) sulfonamide anion (TFSI) alongside a range of cations such as alkyl ammonium have been found to be very thermally stable.^{24, 28} Viscosity and conductivity are important for PILs in different applications^{29, 25} . Dicationic ionic liquids (DILs) have received attention due to their high density of thermal storage improving charge density and an improvement in electrostatic energy.^30-32 Also, they can be less toxic than monocationic equivalents.^{33, 34} Recently, there has been research on the use of anions produced from carboxylates, particularly carboxylic acids, because they are derived from a wide range of environmentally friendly biological sources.^{32, 35} For example, a library of dicationic imidazolium-based dicarboxylate ILs was reported by Kuhn et al.³² Although research on DILs has increased, much of the work so far has focused on imidazolium-based carboxylate ILs. The invention relates to a new family of diamine-based carboxylate ILs. Colaino et al (ChemSusChem 2014, 7, 45-65) have written a review on poly(ethylene glycol) (PEG) based ionic liquids as alternative solvents (incorporated herein by reference in its entirety).³⁶ Many of these PEG based ILs contain quaternary nitrogen cations, conventional imidazole units in between two PEG chains as well as in the centre of the molecules. There is one report of two imidazole units and the two termini of the PEG chain ³⁷ however, these IL are prepared via a complex reaction scheme involving three or more steps using many organic solvents including toluene and ethanol at elevated temperatures thus impacting on the sustainability of the system in its entirety. Indeed, it is often overlooked that the synthesis of ionic liquids often uses solvents and temperatures which are actually counter to the philosophy of Green and Sustainable chemistry. US 9,717,668B describes a wide range of different active agents which are applied to hair to reduce damage to hair following treatment of it with hair relaxing treatments such as peroxide-containing hair treatments. Such active agents are produced and used in aqueous solutions and dispersions. The agents are stated to prevent reversion of the hair’s repaired bonds to the free thiol state and to provide a mixture of reversible covalent and non-covalent (salt) interactions. The Inventors were looking for possible alternative chemistries to be used in the reversible vulcanisation of polydienes (natural and synthetic rubber), so as to enable recycling. This traditionally uses the presence of thiols and disulphides and heating which results in the cross-linking of the polydiene molecules. They identified that the active agents could potentially be used in this application. In contrast to hair treatments, the chemistry needed to be adapted for the use in rubber and carried out in the absence of water. The Inventors therefore produced 4,7,10- trioxatridecane1,13-diamine dimaleate in aqueous solution and subsequently removed the water and the product formed. Unexpectedly, instead of the solid salt expected by the Inventors, a liquid was observed. Further investigation showed that this was not due to residual solvent, but due to the discovery of a new class of ionic liquids. The invention provides a family of ionic liquids comprising a polyether diamine carboxylate or a polyether triamine carboxylate. The polyether amine may be branched or unbranched. The terminal amine residues are typically protonated to form ammonium ions, that is the ionic liquid is typically in the form of a polyether di-ammonium or a carboxylate tri-ammonium carboxylate. The ionic liquid is typically liquid at ambient temperatures, typically 15°C – 30°C, most typically 25°C. Typically, the ionic liquid is a liquid between 0°C and 100°C. Typically, the ionic liquids are substantially stable below 125°C, below 120°C or below 115°C or below 110°C. Above such temperatures, the compounds may decompose to form solids typically by formation of amides with the evolution of water. Typically, the ionic liquid is substantially water-free. That is, the amount of water is typically below 2% water content, more typically below 1.85, 1.5, 1, 0.8, 0.6, 0.5, 0.4 or 0.3% as measured by the Karl-Fischer titration (for example as described herein). The ionic liquid may be a polyether diamine where in the polyetherdiamine or polyethertriamine has the structure: +3HN-A-NH3⁺ or

where A comprises a branched or unbranched polyether. The polyether is typically a poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), or a PEG-PPG, PEG-PPG-PEG copolymer. The ability to change the polyether allows, for example, properties such as the hydrophobic or hydrophilic nature of the ionic liquid to be varied. The number of ether residues in the polyether is typically between 2 and 50, more typically 5 and 40, 10 and 30, 15 and 25, or 2, 3, 4 or 5 ether residues. The molecular weight of the polyether diamine or polyether triamine may be between 134 and 5500, more typically of 50-4500, 250-4000, 350-3500, 450-3000, 550-2500, 500- 2000, 550-2000, 600-1500, 750-1000. The ionic liquid may be obtainable by reacting a polyether diamine, or polyether triamine with a carboxylic acid. Typically, the polyether diamine or polyether triamine is selected from a polyether diamine or polyether triamine selected from:

and x, y and z are independently integers;

and n are independently integers;

and n is an integer of 0 to 20 and x, y and z are independently integers;

and n, m and o are independently integers; wherein: one or more of the poly(propylene oxide) moieties may be replaced by one or more poly(ethylene oxide) moieties or one or more of the polyethylene oxide moieties may be replaced by one or more polypropylene oxide moieties. Where m, n and o are between 1 and 50, 1 and 40, 1 and 30, 1 and 20 or 1 and 10. Typically, the polyether diamines or polyether triamines do not comprise one or more imidazole moieties or indeed contain any cyclic or aromatic chemical entities. The ionic liquid may be a 4,7,10-trioxatridecane 1,13-diamine dicarboxylate or a 4,9- dioxadodecane-1,12- diamine dicarboxylate. The carboxylate is selected from a C1-C20, branched or unbranched, saturated or unsaturated or aromatic carboxylic acid. More typically, the carboxylate is C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11 or C12. The carboxylate may be a monocarboxylate or a dicarboxylate. More typically, the carboxylate is a monocarboxylate. The carboxylate optionally is not maleate. The invention also provides a method of producing an ionic liquid as defined above, comprising reacting a polyether diamine or a polyether triamine with a carboxylic acid. The polyether diamine or polyether triamine may be as defined above. The carboxylic acid may be a C1-C20, branched or unbranched, saturated or unsaturated or aromatic carboxylic acid. Typically, this is a C1, C2, C3, C4, C5, C6, C7, C8, C9, C10 carboxylic acid. It may be a monocarboxylic acid or dicarboxylic acid, most typically a monocarboxylic acid. Optionally, this is not maleic acid or form maleate. The invention also provides the use of an ionic liquid of the invention as an ionic liquid. Use of the ionic liquid of the invention is also provided when used as a solvent. The solvent may be used in an organic synthesis reaction. Methods of using the ionic liquid of the invention as a solvent and/or in an organic synthesis reaction are also provided. The ionic liquid may be substantially hydrophobic immiscible with water and an aqueous solvent is used to extract one or more components from a mixture of reactants or products in the organic synthesis reaction. That is, an aqueous solvent may be used to selectively remove the reactants or products whilst still leaving behind the ionic liquid. This is advantageous because one environmental problem of current ionic liquids is that organic solvents are still often required to remove the reactants or products from the ionic liquid. This still produces environmental concerns due to, for example, the solvent’s toxicity, flammability, or volatility. The organic synthesis reaction may be a Heck reaction. The Heck reaction is the chemical reaction of an unsaturated halide or triflate with an alkene in the presence of a base and a palladium catalyst to form a substituted alkene. Imidazole-based PEG-based di-cationic ionic liquids have been previously studied (Wang et al Synlett 2005, 1861-1864 incorporated here in its entirety). The organic synthesis reaction may be a Suzuki coupling reaction. This is a cross-coupling reaction, where the coupling partners are boronic acid and an organohalide, with a palladium (zero) complex. This has been studied by, for example, Wong H. T. et al (Chem. Eng. Sci. 2006, 61, 1338-1341) and Liu N. et al (Green Chem. 2012, 14, 592-597, hereby incorporated in their entirety). The organic reaction may be a rhodium-catalysed reaction, such as hydrogenation, hydrosilylation or hydroformylation. Imidazole based polyethers, have been used, for example, in the reaction of styrene and triethoxysilane with a rhodium salt (Wu C. et al Catal. Commun. 2008, 10, 248-250, incorporated herein in its entirety). Tan B. et al (Appl. Organomet. Chem. 2008, 22, 620-623 and Zeng Y. et al Catal. Commun. 2012, 19, 70- 73, incorporated herein in their entirety). These use PEG-based rhodium-catalysed reactions using imidazol-based polyethers. The organic synthesis reaction may be a copper-catalysed reaction, such as the amination of halides or Huisgen cycloaddition. Hu Y.-L. et al (J. Chin. Chem. Soc. 2010, 57, 604-611, incorporated herein in its entirety), describes the amination of organic halides in a biphasic system consisting of a PEG-based ionic liquid and methylcyclohexane in the presence of a copper catalyst. The Huisgen cycloaddition reaction is a cycloaddition between an azide and a terminal or internal alkyne to give a 1,2,3-triazole. This has been described using a PEG-based monoammonium mesylate salt (see, for example, Vecchi A. et al, Synthesis Stuttgart 2010, 12, 2043-2048, incorporated herein in its entirety). Venturello catalysts may be used in the organic synthesis reaction, as demonstrated using imidazole-substituted PEG ionic liquids (see, for example, Wang Y. et al, Austr. J. Chem. 2013, 66, 586-593, incorporated herein in its entirety). The organic synthesis may also be an organocatalyzed reaction, such as a Michael reaction or a Knoevenagel condensation (see, for example, Meclarova M. et al, Monatsh. Chem. 2007, 138, 1181-1186) or Luo J. et al, New J. Chem. 2013, 37, 269-273, incorporated herein in their entirety). Multi-component reactions may also be carried out using the ionic liquids of the invention. They are especially useful in the synthesis of heterocycles and complex structures in a single operation. They provide a straightforward preparation in very diverse molecules. See, for example, Hakkou H. et al, Tetrahedron, 2004, 60, 3745-3758, Zhi H. Z. et al, Chem. Commun. 2009, 2878-880 and Fang D. et al, Catal. Sci. Technol. 2011, 1, 243- 245, incorporated herein in their entirety). The organic synthesis reaction may be an aromatic substitution reaction as demonstrated by Wang P.C. and Liu M. Tetrahedron Lett., 2011, 52, 1452-1455; Hu Y.L. et al, J. Iran. Chem. Soc. 2011, 8, 131-141; and Hu Y.-L. et al, ChemCat Chem., 2010, 2, 392-396, incorporated herein in their entirety). The ionic liquids of the invention may also be used in the synthesis of organic compounds from carbon dioxide. The recovery and use of CO2 in chemistry has become an innovative, important approach to find solutions of sustainable development. CO2 can be transformed chemically to prepare new organic molecules that are useful as solvents or intermediates for organic synthesis. PEG-ionic liquids have been reported using PEG-supported phosphonium, as discussed, for example, in the articles by Wang Z. et al (Green Chem. 2012, 14, 519-527; Zhao Y. -N. et al, Catal. Today, 2013, 200, 2-8; and Tian J. -S. et al, Green Chem. 2007, 9, 566-571, incorporated herein in their entirety). In some cases the ionic liquid may accelerate the rate of reaction acting as a catalyst as well as a solvent but not directly participating in the chemical transformations. The organic synthesis reaction may also be a hydrolysis reaction, a fluorination reaction, a reaction protecting carbonyl compounds, or a peptide synthesis, as described in, for example, Hu Y.L. et al, New J. Chem. 2011, 35, 292-298; Jadhav V.H. et al, Org. Lett. 2011, 13, 2502-2505; Wren Y.-M. and Cai C., Tetrahedron Lett. 2008, 49, 7110-7112; and Petiot P. et al, Chem. Commun. 2010, 46, 8842-8844, incorporated herein in their entirety). The ionic liquid may also have potential as a person care product. As discussed above, the compounds have the potential to be used in, for example, the care and protection of, for example, skin, nail, or hair. The ionic liquids of the invention may also have potential uses in batteries as shown by their cyclic voltammetry properties. Accordingly, a battery comprising an ionic liquid of the invention may also be provided. In addition they may be used in any application where ionic liquids are employed. The invention will now be described by way of example only with reference to the following figures: Fig. 1 TGA graph of ILs, under nitrogen from 30°C to 600 °C at a rate of 10 °C/min in 90 μL alumina pans. Fig. 2 DSC of [TTDDA][HexA], under nitrogen from -100 °C to 220 °C at a rate of 10 °C/min in an aluminium pan. Fig. 3 Average viscosity (η) of ILs at 25 °C, 35 °C and 45 °C at a shear rate of 25 S^-1. Fig. 4 Viscosity (η) as a function of temperature for ILs studied in this work. Fig. 5 Average conductivity of ILs at 25 °C, 35 °C and 45 °C. Fig. 6 Conductivity as a function of temperature for the ILs studied in this work. Fig. 7 Cyclic voltammograms of 50 mM Fe(III) in [TTDDA][MA] at a glass carbon electrode with various scan rates at 358 K. Fig. 8 The plot of ip,c versus v^1/2 of [TTDDA][MA]. Fig 9 ¹H NMR (400 MHz, DMSO-d6) spectrum of TTDDA, PA and [TTDDA][PA]. Experimental Section Materials 4,7,10-Trioxa-1,13-tridecanediamine (Trioxa-TDD, 97%), (JEFFAMINE D-230, average Mwt ~230) acetic acid (AA, ≥ 99%), butyric acid (BuA, , ≥ 99%), valeric acid (VA, ≥ 99%), hexanoic acid (HexA, ≥ 99%), heptanoic acid (HepA, ≥ 99%), benzoic acid (BenA, 99%), octanoic acid (OA, ≥ 98%), potassium ferricyanide (K3Fe(CN)6, 99%) were all purchased from Sigma-Aldrich, were used without further purification. Formic acid (FA, ≥ 98%), propionic acid (PA, ≥ 99%) were all from Fluka, and maleic acid (MA, Fisher Scientific, 99%) was used as received. Deionised water was used for the preparation of aqueous solutions (15.6 MΩ, VEOLIA Elga Purelab). Instruments and analysis NMR NMR spectra were obtained on a Bruker DPX-400 and Bruker AV III-500 spectrometers at ambient temperature to confirm the production of the expected carboxylate. Polymer samples were dissolved in deuterated dimethyl sulfoxide (d⁶-DMSO) obtained from Sigma- Aldrich with ca. 100 mg/mL. All chemical shifts are reported in ppm (δ). Data was processed and analysed using the ACD/NMR software. Differential scanning calorimetry (DSC) DSC measurements were performance on a TA DSC with autosampler. Measurements were carried out under nitrogen. DSC measurements of ionic liquids samples were carried out < -100 to 220 °C at a rate of 10 °C/min in an aluminium pan. Thermogravimetric analysis (TGA) TGA was performed on a TA TGA with autosampler. Measurements were carried out under nitrogen from 30 °C to 600 °C at a heating rate of 10 °C/min in a 90 μL alumina pan. Except [Trioxa-TDD][Maleic acid] was analysed at a heating rate of 2 °C/min. Thermogravimetric analysis (TGA-MS) The sample were run on Mettler-Toledo TGA/DSC with autosampler and Hiden HPR20 Mass Spectrometer. The TGA was performed under a 20 mL / min nitrogen atmosphere at temperatures between 25 to 600 °C at a ramp rate of 5 °C / min. The Mass Spectrometer was run with a multiplier voltage of 1123 V, with a scan range of 1 to 100 m/z. The samples were prepared in 70 µL alumina pans. Rheometry Viscosity was measured using an Anton Paar MCR 320 rheometer equipped with a plate to plate configuration with diameter of 25 mm with RheoCompass software. Fourier-Transform infrared spectroscopy (FT-IR) FT-IR measurements were performed on a Shimadzu Spirit IR equipped with a SpecAc Golden Gate ATR. The wavelength was from 500 to 4000 cm^-1, with 40 scans at 4 resolution. Conductivity Ionic conductivity was measured using a Mettler Toledo SevenGo Duo conductivity meter and an InLab 738-ISM-5M conductivity probe. At 25 °C, the electrodes were calibrated using Mettler Toledo’s calibration standards. Cyclic Voltammetry (CV) Cyclic voltammetry was performed on a CH-Instruments 600E potentiostat with a 3 mm glassy carbon disc electrode polished with 0.05 m alumina powder and rinsed with acetone, ethanol, and MilliQ water before each use. A platinum wire coil served as the counter electrode. The reference electrode was Ag/AgCl, and the silver wire was polished and cleaned with acetone, ethanol, and MilliQ water in that order. The wire was then placed in a glass capillary tube equipped with a vycor frit and filled with a 3 M KCl solution. The ILs with 50 mM of potassium ferricyanide were added. Karl-Fischer titration Mettler Toledo Karl-fisher titrator was used for the determination of ionic liquids water content with range from 100 ppm to 100%. Hydranal Coulomat AG was used as titration reagent. For analysis, 1 mL of 20 w/w% solutions of the ILs in methanol were injected (A. W. Tamar L. Greaves, Celesta Fong, Irena Krodkiewska, and and C. J. Drummond, J. Phys. Chem. B, 2006, 110, 22479-22487), and mixing method was used with a magnetic stirring bar. Synthetic Procedures 4,7,10-Trioxa-1,13-tridecanediamine (TTDDA) of Jeffamine D-230, average molecular weight approx.. 230 g/mol^-1(1 equiv), acid (2 equiv) and 20 wt% water was added into round-bottom flask along with a stir bar. The reaction was carried under room temperature. After 24 hours, the water was removed by rotary evaporation for 4 hours (27 mbar; 50 °C) before thermal, viscosity, and electrochemical characterization. In a separate reaction the water was removed by freeze drying overnight. Results and Discussion Synthesis These protic ionic liquids (PILs) were prepared via the stoichiometric combination/mixing of a trioxa-1,13-tridecanediamine, an inexpensive and readily available diamine, and a simple Brønsted acid (Scheme 1). Reactions were monitored using ¹H NMR with the disappearance of the proton signal from propionic acid for example, (CH3-CH2-COOH) at 11.9 ppm indicating the formation of the propionate (CH3-CH2-COO-), Figure 9, supporting information. Furthermore, the peak shifting from 1.2 ppm to 6.8 ppm demonstrates that the amine (H2N-(CH2)3-O-(CH2)2-O-(CH2)2-O-(CH2)3-NH2) was successfully protonated to an ammonium salt (H3N⁺-(CH2)3-O-(CH2)2-O-(CH2)2-O-(CH2)3-N⁺H3). Water is the by- product of the reaction as measured by Karl-Fisher (KF) titration. Water is easier to remove from these ILs with linear monoanions when the alkyl chain length is increased, table 1.

Scheme 1 Synthesis of dicationic diamine-based carboxylate ionic liquids: OOCR’ = formate (FA), acetate (AA), propionate (PA), butyrate (ButA), maleate (MA), valerate (VA), hexanoate (HexA), heptanoate (HepA), benzoate (BenA) and octanoate (OA).

Table 1 Water content and physical appearance of the ILs. Karl-fisher Ionic liquid Ionic liquid abbrev (%) Physical appearance 4,7,10-Trioxa-1,13-tridecanediammonium formate [TTDDA][FA] 1.84 Colourless liquid 4,7,10-Trioxa-1,13-tridecanediammonium acetate [TTDDA][AA] 1.83 Viscous pale yellow liquid 4,7,10-Trioxa-1,13-tridecanediammonium propionate [TTDDA][PA] 1.83 Viscous pale yellow liquid 4,7,10-Trioxa-1,13-tridecanediammonium butyrate [TTDDA][ButA] 1.83 Viscous pale yellow liquid 4,7,10-Trioxa-1,13-tridecanediammonium maleate [TTDDA][MA] 1.81 Viscous colourless liquid 4,7,10-Trioxa-1,13-tridecanediammonium valerate [TTDDA][VA] 1.44 Viscous pale yellow liquid 4,7,10-Trioxa-1,13-tridecanediammonium hexanoate [TTDDA][HexA] 0.79 Viscous pale yellow liquid 4,7,10-Trioxa-1,13-tridecanediammonium heptanoate [TTDDA][HepA] 0.41 Viscous pale yellow liquid 4,7,10-Trioxa-1,13-tridecanediammonium benzoate [TTDDA][BenA] 1.83 Viscous colourless liquid 4,7,10-Trioxa-1,13-tridecanediammonium octanoate [TTDDA][OA] 0.57 Viscous pale yellow liquid

Heating 4,7,10-Trioxa-1,13-tridecanediammonium propionate ([TTDDA][PA]) at 220°C for 6 hours leads to the intramolecular condensation of the PIL to form a diamide, as observed by ¹H NMR (Scheme 1). The peak from the ammonium salt (δ = 6.8 ppm) shifts to the amide peak (δ = 7.8 ppm) on completion. Fourier transform infrared (FT-IR) also supports the synthesis of the amide; (figure S91, supporting information). The νN-H in the amine is shown by the weak broad band on 3410 cm^-1. After heating, there is a very strong and broad band assigned to the amide in the range of 3100 to 3500 cm^-1. Solubility The solubility of these ILs in commonly used solvents was determined. Common representative organic solvents were selected with a range of relative polarity water: 1.00; TFE: 0.90; methanol: 0.76; ethanol: 0.65; DMSO: 0.44; DMF: 0.39; acetone: 0.35; DCM: 0.31; chloroform:0.25; THF: 0.21; toluene: 0.10 and hexane: 0.01³⁸. Each IL was dissolved in 0.1 g amounts and was given the following solubility ratings: good in 1 mL of the solvent, medium in 3 mL of the solvent, and poor when insoluble in 3 mL at 25 °C and ambient pressure.³² The ILs were generally more soluble in solvents with higher relative polarity such as water and methanol, table 2. Low solubility was observed in aprotic polar solvents (acetone, chloroform) and nonpolar solvents (toluene, hexane) whereas DMSO, which was miscible with all ILs. The presence of the anionic carboxylate group facilitates miscibility in polar protic solvents.³² Additionally, increasing the length of the alkyl group increased the solubility with [TTDDA][HepA] and [TTDDA][OA] being soluble in the widest range of solvents. The presence of dianions ([TTDDA][MA]) or ring structures ([TTDDA][BenA]) in the ILs leads to poorer solubility than their linear analogues ([TTDDA][ButA] and [TTDDA][HepA]).

Table 2 Solubilities of ILs in common solvents.

Thermal stability The thermal stability of an IL is an important parameter in many applications.^{39, 40} Several factors can affect the thermal stability of the ILs including cation modification, as well as cation and anion types.⁴¹ In the present case, the anion is a carboxylate with alkyl chain length ranging from one to eight carbons. The onset temperature (Ton) obtained from thermogravimetric analysis (TGA) is taken as the thermal decomposition temperature of the IL.^{32, 39-41} The TGA traces of the ILs (Figure 1 and Table 3) show a Ton over the range of 30 °C to 600 °C with more than one apparent decomposition step. Water loss is the first mass loss step, observed between 130 °C and 240 °C. There is visual evidence of a condensation reaction presumably to the amide in the TGA pan. Taking the second Ton as the main thermal degradation step, following amide formation, (Figure 1 and Table 3), it was observed that increasing the alkyl chain of the anion resulted in a decrease in thermal stability from [TTDDA][FA] to [TTDDA][PA]. The increase of the alkyl chain from [TTDDA][ButA] to [TTDDA][OA] leads to an increase in the thermal stability of the IL through lower hydrophilicity of the anion, figure 1 and table 3. Based on their Ton, it is evident that the IL of a linear monoanion ([ButA]-) is less thermally stable than its analogues with dianions ([MA]-). Additionally, the thermostability of the IL can be enhanced by substituting the linear anion ([HepA]-) with one containing an aromatic ring ([BenA]-) (figure 1 and table 3). Table 3 Characterisation of TGA data for ILs, under nitrogen from 30°C to 600 °C at a rate of 10 °C/min in 90 μL alumina pan.

Thermal-Phase change Behaviour Glass transition temperatures (Tg) were determined by differential scanning calorimetry (DSC).³² A library of 10 ILs manifested solid-liquid and liquid-solid transitions, table 4, suggesting these ILs exhibited both an amorphous and crystalline phase (see supporting information for DSC curves). In the case of [TTDDA][HexA], figure 2, the first heating cycle reveals a Tg at -70 °C (heating rate of 10 °C/min) with a water loss step between 120 to 220 °C indicating a condensation reaction of the [TTDDA][HexA] IL to the diamide. The phase change is seen as a Tg shift to -73 °C on the second heating cycle and both crystallisation and the melting points are observed. All ILs (table 4) showed a Tg only during the first heating cycle, which suggests that the material is amorphous⁴². [TTDDA][FA] exhibited the lowest Tg (-75 °C), whereas [TTDDA][AA] showed the highest Tg (-54°C) of all the ILs with linear monoanions. The Tg of the ILs can be increased either by substituting the dianion (maleic acid) with a monoanion (butyric acid) or by using an anion with an aromatic structure (benzoic acid) rather than a linear one (heptanoic acid), table 4. A low Tg is expected to lead to favourable physicochemical features such as low viscosity and good ionic conductivity⁴² . Following complete removal of water from the condensation reaction two different behaviours were observed in the second heating cycle. Firstly, ILs exhibiting a glass transition, indicating that the amide produced following the reaction the product remains amorphous, more than half were in this category: [TTDDA][FA], [TTDDA][AA], [TTDDA][PA], [TTDDA][ButA], [TTDDA][MA] and [TTDDA][BenA]. The second behaviour showed a glass transition, crystallisation, and subsequent melting temperature, [TTDDA][VA], [TTDDA][HexA] and [TTDDA][HepA]. A further family of ILs were synthesized with Jeffamine D-230, a polyether amine in place of TTDDA exhibited thermal properties similar to the former group. It is noted that there are many different commercially available polyether amines which should show similar behaviour, Table 4. Table 4 Characterisation of DSC data for the ILs, under nitrogen from -100 °C to 220 °C at a rate of 10 °C/min in an aluminium pan. Table 4 1^st heating cycle 2^nd heating cycle ΔHm Ionic liquid Tg (°C) Tg (°C) Tc (°C) ΔHc(J/g) Tm(°C) (J/g) [TTDDA][FA] -75 -66 N/A N/A N/A N/A [TTDDA][AA] -55 -64 N/A N/A N/A N/A [TTDDA][PA] -69 -65 N/A N/A N/A N/A [TTDDA][ButA] -70 -75 N/A N/A N/A N/A [TTDDA][MA] -66 -8 N/A N/A N/A N/A [TTDDA][VA] -70 -69 9 26 51 25 [TTDDA][HexA] -70 -73 -19 140 56 188 [TTDDA][HepA] -62 -76 -27 14 63 43 [TTDDA][BenA] -54 -23 N/A N/A N/A N/A [TTDDA][OA] -62 N/A N/A N/A 7; 72 9; 33 [JEFFAMINE][AA] -37 -52 N/A N/A N/A N/A [JEFFAMINE][PA] -36 -63 N/A N/A N/A N/A [JEFFAMINE][HepA] -64 -51 N/A N/A N/A N/A [JEFFAMINE][OA] -57 -56 N/A N/A N/A N/A Temperature Dependence on Shear Viscosity Viscosity was measured between 25 °C and 45 °C, Table 5⁴². Each IL showed Newtonian behaviour within this temperature range (figure S92 and S93, supporting information), figure 3. This decrease in viscosity on increasing temperature is in agreement with Khan et al.⁴². The viscosities for [TTDDA][ButA], [TTDDA][MA], [TTDDA][HepA], [TTDDA][BenA] are 1140, 6132, 6227, and 15940 mPa·s at 25 °C respectively, table 5. Analogues with linear monoanions, [TTDDA][MA] and [TTDDA][BenA] have higher viscosities. Increasing the alkyl chain length did not directly correlate with a specific trend in viscosity⁴³. A plot of ln η vs. 1/T gives the activation energy (Eη) for the ILs (Figure 4 and Table S1.). [TTDDA][MA] and [TTDDA][BenA] have higher Eη values, presumably due to stronger electrostatic interactions between their anions and cations⁴⁴. The estimated Eη values for the ILs synthesized in this work range from 12 to 28 KJ·mol^-1. Table 5 Average viscosity (η) of ILs at 25 °C, 35 °C and 45°C at shear rate of 25 S^-1.

Temperature Dependence on Shear Viscosity The ionic conductivity is dependant upon viscosity, ion dissociation degree, ionic charge, and ion mobility and is important for many applications. ^{45, 46} The ionic conductivity was measured at 25 °C, 35 °C and 45 °C showing values between 6.64 x 10^-3 to 2.98 mS.cm- ¹, figure 5 and table 6. The conductivities increased slightly as temperature increased. Changing the chain length of the anion did not significantly affect conductivity, however, it varied considerably when rigidity was introduced into the anion. For example, when the anion was changed from [MA]- to [ButA]-, the conductivity decreased from 0.18 to 5.31 x 10^-2 mS.cm^-1, at 25 °C. Conductivity followed the Arrhenius equation in logarithmic form, lnλ = lnλ0 + Ea/RT, with Ea and λ0 indicating the activation energy of conductivity and limiting conductivity, respectively, in the temperature range of 25 to 45 °C, figure 6. They all demonstrate a weak dependence on the anion’s alkyl length and a stronger dependence on the anion’s change from linear to dianion or ring structure. [TTDDA][FA] showed the highest ionic conductivity, with 1.25 mS.cm^-1 at 25 °C (table 6). In general, the series of ILs with the lowest viscosity had the highest ionic conductivity, which is consistent with earlier studies by Greaves et al.⁴⁶ Table 6 Average conductivity of ILs at 25 °C, 35 °C and 45 °C.

Electrochemical stability The electrochemical stability of the ILs was investigated by cyclic voltammetry (CV) ⁴⁷ provided a working electrochemical window of 1.2 V (-0.6 V to 0.6 V) with the presence of potassium ferricyanide (K3Fe(CN)6).⁴⁸ In order to counteract the high viscosity and hygroscopic nature of these ILs, the electrochemical cell was kept at 358 K during the experiment, figure 7 and supporting information. As the scan rate increases from 0.05 to 0.4 V/s, the reduction peak (Ep,c) becomes more negative and the cathodic peak current (ipc) rises, Figure 7. With a scan rate of 0.05 V/s, the peak separation (Δ E = Ep,a-Ep,c) was found to be 0.226 V increasing at higher scan rates. Conversely, the average peak potential (E1/2 = (Ep,c + Ep,a)/2) remains constant at all scan rates, figure 7 and table 7. In all cases as the scan rate is increased, the reduction and oxidation peak potentials increasingly move apart with (Ep,c) shifting to a more negative potential and (Ep,a) increasing. These results demonstrate that the Fe(III)/Fe(II) reduction in an IL medium at a GC electrode is quasi-reversible and governed by both charge transfer and diffusion processes.⁴⁸ The Randles-Sevcik equation (eq 1) can be used to calculate the diffusion coefficient for electrochemically reversible electron transfer processes that involve freely diffusing redox species such as Fe(III)/Fe(II) as applied to a quasi-reversible systems,^{47- 49}

where ip,c (A) is the cathodic peak current, n the number of electrons transferred in the redox event, F (C/mol) the Faraday constant, A (cm²) the electrode surface area, C⁰ the concentration of Fe(III) ion (mol/cm³), v (V/s) the scan rate, Do (cm²/s) the diffusion coefficient, R (J/K/mol) the gas constant and T (K) is the absolute temperature. The diffusion coefficient at 358 K of each IL are reported in table S4. Cathodic peak current (ip,c) increases with increasing scan rate (v). Faster scan rates cause a reduction in the size of the diffusion layer, resulting in larger currents.⁴⁷ The Randles-Sevcik equation also illustrates how cathodic peak current (ip,c) increases linearly with the square root of the scan rate (v^1/2), figure 8 shows the linear plot of ip,c against v^1/2. Table 7 Cyclic voltammograms of Fe(III)/(Fe(II) reversible couple in [TTDDA][MA] at a glassy carbon electrode at 358 K.

We illustrate the invention with a family of ten new dicationic ionic liquids (DILs) and four DILs with a polyether amine of nominal molecular weight 270 g mol^-1 with the same dication, protonated trioxa-1,13-tridecanediamine([TTDDA], and different simple anions synthesised by the simple mixing of inexpensive reagents which have been analysed using ¹H and ¹³C NMR and LC-MS. The DILs show a good temperature window where thy remain as free flowing liquids but on heating in excess of approximately 120 °C they undergo a condensation reaction to a diamide and further thermal degradation at higher temperatures. Replacing a linear acyclic anion with one that has an aromatic ring or a dianion such as maleic anhydride both the thermostability and glass transition temperature are enhanced. 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Claims

CLAIMS 1. An ionic liquid comprising a polyetherdiamine carboxylate or a polyethertriamine carboxylate.

2. An ionic liquid according to claim 1 where in the polyetherdiamine or polyethertriamine has the structure: +3HN-A-NH3⁺ or

where A comprises a branched or unbranched polyether.

3. An ionic liquid according to claims 1 or 2 wherein the polyether is a polyethylene glycol, polypropylene glycol or a polyethylene-polypropylene glycol or polyethylene-polypropylene-polyethylene glycol copolymer.

4. An ionic liquid according to any preceding claim wherein the number of ether residues in the polyether is between 2 and 50.

5. An ionic liquid according to any preceding claim wherein the molecular weight of the polyetherdiamine or polyethertriamine is 134 to 5500.

6. An ionic liquid according to any preceding claim wherein the polyetherdiamine or polyethertriamine is obtainable by reacting a polyetherdiamine or polyethertriamine with a carboxylic acid.

7. An ionic liquid according to claim 6, wherein the polyetherdiamine or polyethertriamine is selected from:

and x, y and z are independently integers;

and n are independently integers;

and n is an integer of 0 to 20 and x, y and z are independently integers;

and n, m and o are independently integers; wherein: one or more of the polypropylene oxide moieties may be replaced by one or more polyethylene oxide moieties or one or more of the polyethylene oxide moieties may be replaced by one or more polypropylene oxide moieties.

8. An ionic liquid according to any preceding claim, which is a 4,7,10- trioxatridecane1,13-diamine dicarboxylate or a 4,9-dioxadodecane-1,12- diamine dicarboxylate.

9. An ionic liquid according to any preceding claim wherein the carboxylate is selected from a C1 to C20, branched or unbranched, saturated or unsaturated, or aromatic carboxylate.

10. An ionic liquid according to any preceding claim wherein the carboxylate is a monocarboxylate or a dicarboxylate.

11. An ionic liquid according to any preceding claim substantially free of water <2 wt% as determined by Karl Fisher titration.

12. An ionic liquid according to any preceding claim which is stable below 120’C.

13. A method of producing an ionic liquid according to any preceding claim, comprising reacting a polyetherdiamine or a polyethertriamine with a carboxylic acid.

14. A method according to claim 13 comprising removing water from the product of the reaction of a polyetherdiamine or a polyethertriamine with a carboxylic acid.

15. Use of an ionic liquid according to claims 1 to 12 as an ionic liquid.

16. Use of an ionic liquid according to claims 1 to 12 as a solvent.

17. Use according to claim 16, where in the solvent is used as a solvent in an organic synthesis reaction.

18. Use according to claim 17, wherein the ionic liquid is hydrophobic and an aqueous solvent is used to extract one or more components from a mixture of reactants or products in the organic synthesis reaction.

19. Use according to claim 17, wherein the organic synthesis reaction is a Heck reaction; a Suzuki coupling reaction; a rhodium catalysed reaction selected from a hydrogenation, a hydrosilylation, and a hydroformylation reaction; a copper catalysed reaction selected from halide amidation and Huisgen cycloaddition; as a Venturello catalyst; organocatalysis; in a multicomponent reaction; aromatic substitution reaction; synthesis of organic compounds from carbon dioxide; or an addition reaction.

20. Use of an ionic liquid according to claims 1 to 12 in a personal care product.

21. A personal care product comprising an ionic liquid according to claims 1 to 12.

22. A personal care product according to claim 21 which is a skin, nail or hair care product.

23. A battery comprising an ionic liquid according to claims 1 to 12.