Publications
255 results found
De Gregorio GF, Weber CC, Gräsvik J, et al., 2016, Mechanistic insights into lignin depolymerisation in acidic ionic liquids, Green Chemistry, Vol: 18, Pages: 5456-5465, ISSN: 1744-1560
Acidic anions of ionic liquids have been demonstrated as efficient catalysts for the cleavage of the β-O-4 ether linkage prevalent in the lignin superstructure. Through the use of lignin model compounds with varying functionality and by monitoring reaction kinetics, a full mechanistic investigation into the hydrolysis of the β-O-4 linkage in acidic ionic liquid solutions is reported. Hammett acidities are reported for different 1-butyl-3-methylimidazolium hydrogen sulfate [C4C1im][HSO4] ionic liquid systems with varying acid and water concentrations and were correlated to substrate reactivity. Results show that the rate of ether cleavage increases with an increase in acidity and the initial dehydration of the model compound is the rate-determining step of the reaction. The Eyring activation parameters of the reaction in hydrogen sulfate ionic liquids with a variety of cations are reported, indicating a consistent E1 dehydration mechanism. Hydrogen bonding in protic ionic liquids was shown to significantly influence anion–cation interactions, consequently altering the solvation of the protonated starting material and therefore the overall rate of reaction. Comparison of reaction rates in these ionic liquids with results within aqueous or aqueous/organic media indicate that the ionic liquids facilitate more rapid cleavage of the β-O-4 ether linkage even under less acidic conditions. All the reported results give a complete overview of both the mechanistic and solvation effects of acidic ionic liquids on lignin model compounds and provide scope for the appropriate selection and design of ionic liquids for lignin processing.
De Gregorio GF, Prado R, Vriamont C, et al., 2016, Oxidative Depolymerization of Lignin Using a Novel Polyoxometalate-Protic Ionic Liquid System, ACS Sustainable Chemistry and Engineering, Vol: 4, Pages: 6031-6036, ISSN: 2168-0485
Oxidative depolymerization of lignin obtained from pine and willow can be achieved in a novel system encompassing the ionic liquid (IL) 1-butylimidazolium hydrogensulfate coupled with a vanadium based polyoxometalate (POM) under oxygen rich conditions. Along with an array of phenols and functionalized aromatics, vanillin and syringaldehyde were the main products extracted from the IL. The overall yield of aldehyde products were shown to be higher on lignin samples obtained with shorter pretreatment times, with vanillin being the exclusive aldehyde product obtained from pine. In the presence of molecular oxygen, the highest yield of aldehyde products was obtained when 5 wt % of the POM relative to the IL was employed and constituted the major product in the extracted oils. This system succeeds in exploiting the ability of ILs to depolymerize lignin and the remarkable properties of the POM to oxidize the lignin fragments into useful platform chemicals.
Eyckens DJ, Demir B, Walsh TR, et al., 2016, Correction: Determination of Kamlet–Taft parameters for selected solvate ionic liquids, Physical Chemistry Chemical Physics, Vol: 18, Pages: 19975-19975, ISSN: 1463-9084
Correction for 'Determination of Kamlet-Taft parameters for selected solvate ionic liquids' by Daniel J. Eyckens et al., Phys. Chem. Chem. Phys., 2016, 18, 13153-13157.
Hunt PA, Ashworth C, Matthews R, et al., 2016, Doubly Ionic Hydrogen Bond Interactions Within the Choline Chloride - Urea Deep Eutectic Solvent, Physical Chemistry Chemical Physics, Vol: 18, Pages: 18145-18160, ISSN: 1463-9084
Deep eutectic solvents (DESs) are exemplars of systems with the ability to form neutral, ionic and doubly ionic H-bonds. Herein, the pairwise interactions of the constituent components of the choline chloride–urea DES are examined. Evidence is found for a tripodal CH⋯Cl doubly ionic H-bond motif. Moreover it is found that the covalency of doubly ionic H-bonds can be greater than, or comparable with, neutral and ionic examples. In contrast to many traditional solvents, an “alphabet soup” of many different types of H-bond (OH⋯O[double bond, length as m-dash]C, NH⋯O[double bond, length as m-dash]C, OH⋯Cl, NH⋯Cl, OH⋯NH, CH⋯Cl, CH⋯O[double bond, length as m-dash]C, NH⋯OH and NH⋯NH) can form. These H-bonds exhibit substantial flexibility in terms of number and strength. It is anticipated that H-bonding will have a significant impact on the entropy of the system and thus could play an important role in the formation of the eutectic. The 2 : 1 urea : choline–chloride eutectic point of this DES is often associated with the formation of a [Cl(urea)2]− complexed anion. However, urea is found to form a H-bonded urea[choline]+ complexed cation that is energetically competitive with [Cl(urea)2]−. The negative charge on [Cl(urea)2]− is found to remain localised on the chloride, moreover, the urea[choline]+ complexed cation forms the strongest H-bond studied here. Thus, there is potential to consider a urea[choline]+·urea[Cl]− interaction.
Hunt PA, Welton T, Hallett J, et al., 2016, Solubility of Alkali Metal Halides in the Ionic Liquid [C4C1im][OTf], Physical Chemistry Chemical Physics, Vol: 18, Pages: 16161-16168, ISSN: 1463-9084
The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl,CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li+, Na+and K+salts with anionsmatching the ionic liquid have been also investigated to determine how well these cations dissolve in[C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility ofsalts within this ionic liquid. The highest solubility found was for iodide salts and the lowestsolubility, for the three fluoride salts. There is no outstanding difference in the solubility of salts withmatching anions in comparison to halide salts. The experimental data were correlated employingseveral phase equilibria models, including ideal mixtures, van’t Hoff, the λh (Buchowski) equation,the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that thevan’t Hoff model gave the best correlation results. On the basis of the experimental data thethermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systemstogether with computed gas phase metathesis parameters. Dissolution depends on the energydifference between enthalpies of fusion and dissolution of the solute salt. This demonstrates thatovercoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionicliquids.
Prado R, Erdocia X, De Gregorio GF, et al., 2016, Willow Lignin Oxidation and Depolymerization under Low Cost Ionic Liquid, ACS Sustainable Chemistry and Engineering, Vol: 4, Pages: 5277-5288, ISSN: 2168-0485
Willow biomass was subjected to different pretreatment conditions with triethylammonium hydrogen sulfate as solvent, and the produced lignin solutions were treated by oxidation either homogeneously using H2O2 as oxidant or by heterogeneous catalysis using TiO2. Lignin, residual lignin, oil, and the recovered ionic liquid (IL) were characterized in order to determine the effects of each treatment. Lignin was successfully extracted and depolymerized by oxidation and characterized by ATR-IR, HPSEC, and py-GCMS. The obtained oil was characterized by GCMS; it was composed mainly of acids derived from the sugar and lignin fractions, the TiO2 catalyzed oils being richer in phenolic derived compounds than sugar fractions. The final ionic liquid was characterized in order to determine its suitability to be reutilized.
Saugar AI, Marquez-Alvarez C, Villar-Garcia IJ, et al., 2016, Basicity and catalytic activity of porous materials based on a (Si,Al)-N framework, Applied Catalysis A: General, Vol: 520, Pages: 157-169, ISSN: 1873-3875
Eyckens DJ, Demir B, Walsh TR, et al., 2016, Determination of Kamlet–Taft parameters for selected solvate ionic liquids, Physical Chemistry Chemical Physics, Vol: 18, Pages: 13153-13157, ISSN: 1463-9084
The normalised polarity ENT and Kamlet–Taft parameters of recently described solvate ionic liquids, composed of lithium bis(trifluoromethyl)sulfonimide (LiTFSI) in tri- (G3TFSI) or tetraglyme (G4TFSI) have been determined and compared to the parent glyme (G3 and G4). We show that these solvate ionic liquids have a high polarity (G3TFSI, (ENT) = 1.03; G4TFSI, (ENT) = 1.03) and display very high electron pair accepting characteristics (G3TFSI, α = 1.32; G4TFSI, α = 1.35). Molecular dynamics simulations suggest that the chelated lithium cation is responsible for this observation. The relatively small hydrogen bond acceptor (β) values for these systems (G3TFSI, β = 0.41; G4TFSI, β = 0.37) are thought to be due primarily to the TFSI anion, which is supplemented slightly by the glyme oxygen atom. In addition, these solvate ionic liquids are found to have a high polarisability (G3TFSI, π* = 0.94; G4TFSI, π* = 0.90).
Albrecht T, Godfrey D, Bannock JH, et al., 2016, A robotic platform for high-throughput electrochemical analysis of chalcopyrite leaching, Green Chemistry, Vol: 18, Pages: 1930-1937, ISSN: 1463-9262
Cu extraction from chalcopyrite ores is typically a slow process that involves aggressive chemical reagents with significant environmental impact. Ionic liquids (IL) have been proposed as a potentially more benign solution, but the sheer number of IL variants complicates the search for the most efficient solvent systems. Here, we present an automated electrochemical platform that allows for screening of 180 and more leaching samples in parallel with minimal solvent consumption. In a proof-of-concept study, we screen 25 samples with different IL and water contents, and find two orders of magnitude difference in leaching performance within this array. The best performing system is then applied in a tank leaching configuration, with real-time electrochemical monitoring of Cu evolution in solution. All electrochemical data is found to be in excellent agreement with off-line ICP-AES data.
Welton T, Griffith J, Clough M, et al., 2016, Enhancing the stability of ionic liquid media for cellulose processing: acetal protection or carbene suppression?, Green Chemistry, Vol: 18, Pages: 3758-3766, ISSN: 1463-9262
Although excellent candidate solvents for cellulose, capa-ble of dissolving 20 wt% of the carbohydrate for electro-spinning processes, dialky-limidazolium carboxylate ionic liquids undergo unde-sirable side reactions with the reducing end of saccharides, terminating in an equilibrium concentration of a 2-(hydroxymethyl)-substituted imidazolium ‘adduct’. The addition of small molar quantities of a benign, non-toxic and inexpensive co-solvent, e.g. glycerol, mini-mises the rate of adduct ac-cumulation, thereby enhanc-ing the long-term thermal stability and recyclability of the expensive ionic liquid component. NMR, UV-vis and mass spectrometry ex-periments reveal that the im-proved stability is likely at-tributable to suppression of the transient dialkylimidazol-2-ylidene carbene, via hy-drogen-donation by the pro-tic co-solvent, rather than by cyclic acetal protection of the carbohydrate. The incor-poration of (up to) 10 wt% of glycerol into the solvent mix-ture does not exacerbate the rate of cellulose depolymeri-sation compared to in the neat ionic liquid, and high solubility of cellulose is main-tained. Furthermore, a col-ourimetric comparison of the recovered solvents, following cellulose re-precipitation, demonstrates that glycerol does not increase the concen-tration of contaminant re-ducing sugars in the organic electrolyte.
Vincent SR, Prado R, Koutsomitopoulou A, et al., 2016, Fibre spinning of lingo-cellulose biomass using ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Prado R, Brandt A, Erdocia X, et al., 2016, Depolymerisation of lignin by oxidation in ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Kuzmina O, Welton T, 2016, Physicochemical properties of cellulose-dissolving superbase ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Rahatekar S, Zhu C, Eichhorn S, et al., 2016, Manufacturing strong regenerated cellulose nano-composite fibres, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Welton T, Edel J, McIntosh A, 2016, Ion diffusion in ionic liquids: Single molecule fluorescence spectroscopy, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Wanasekara N, Zhu C, Eichhorn S, et al., 2016, Molecular deformation in high performance cellulose fibres, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Welton T, Matthews RP, Villar-Garcia IJ, et al., 2016, A structural investigation of ionic liquid mixtures, Physical Chemistry Chemical Physics, Vol: 18, Pages: 8608-8624, ISSN: 1463-9084
The structures of mixtures of ionic liquids (ILs) featuring a common 1-butyl-3-methylimidazolium ([C4C1im]+) cation butdifferent anions have been investigated both experimentally and computationally. 1H and 13C NMR of the ILs and theirmixtures has been performed both on the undiluted liquids and these diluted by CD2Cl2. These experiments have beencomplemented by quantum chemical density functional theory calculations and molecular dynamics simulations. Thesetechniques have identified the formation of preferential interactions between H2 of the imidazolium cation and the moststrongly hydrogen bond (H-bond) accepting anion. In addition, a preference for the more weakly H-bond accepting anionto interact above the imidazolium ring through anion-π+ interactions has been identified. The modelling of these data hasidentified that the magnitude of these preferences are small, of the order of only a few kJ mol−1, for all IL mixtures. Noclustering of the anions around a specific cation could be observed, indicating that these interactions arise from thereorientation of the cation within a randomly assigned network of anions. π+-π+ stacking of the imidazolium cations wasalso studied and found to be promoted by ILs with a strong H-bond accepting anion. Stacking interactions are easilydisrupted by the introduction of small proportions (< 50 mol%) of a weakly coordinating anion due to their propensity toform anion-π+ interactions. These results suggest that the formation of IL mixtures with different anions leads to subtlestructural changes of much lower energy than the Coulombic ordering of ions, accounting for why most IL mixtures exhibitideal, or nearly ideal, behaviour.
Welton T, 2016, Much to be proud of, Chemical & Engineering News, Vol: 94, Pages: 3-3, ISSN: 1520-605X
Welton T, 2016, Building an Inclusive Culture in the Chemistry Department at Imperial College, Chemistry-A European Journal, Vol: 22, Pages: 3535-3536, ISSN: 1521-3765
Eyckens DJ, Champion ME, Fox BL, et al., 2016, Solvate ionic liquids as reaction media for electrocyclic transformations, European Journal of Organic Chemistry, Vol: 2016, Pages: 913-917, ISSN: 1434-193X
Solvate ionic liquids (SILs) consisting of lithium bis(trifluoromethylsulfonyl)imide dissolved in tri- or tetraglyme have recently emerged as a novel class of ionic liquids. Herein, the first use of solvate ionic liquids as a replacement for molecular solvents in electrocyclization reactions is reported. The SILs promoted both Diels–Alder and [2+2] cycloaddition reactions, compared to an appropriate molecular solvent, and 5 m lithium perchlorate in diethyl ether. The Gutmann acceptor number (AN) of these solvate ionic liquids has also been determined by 31P NMR spectroscopy to be 26.5, thus being modest Lewis acids.
Clough MT, Geyer K, Hunt PA, et al., 2016, Azoniaspiro salts: towards bridging the gap between room-temperature ionic liquids and molten salts., Physical Chemistry Chemical Physics, Vol: 18, Pages: 3339-3351, ISSN: 1463-9084
In a continued effort to improve the suitability of ionic liquids in applications operating at raised temperatures, novel spirocyclic 'azoniaspiro' salts (with cations derived from five-, six-, seven- and eight-membered rings) are prepared and characterised. The structural and thermal properties of these salts are compared against those of established analogues. The stable geometries and ion pairing behaviour of these species are investigated via a combined experimental/computational approach, employing X-ray crystallography and Density Functional Theory (DFT) methods. Subsequently, the thermal stabilities of these organic salts are characterised and compared using a broad range of techniques. Hyphenated Thermogravimetry-Mass Spectrometry investigations enable complex mechanisms underlying thermal decomposition to be elucidated. Lastly, transition state structures are optimised, corresponding to plausible decomposition mechanisms of the azoniaspiro salt, 6-azoniaspiro[6.5]dodecanium chloride, and one prototypical monocyclic species 1-butyl-1-methylpiperidinium chloride, using DFT. The observed improved thermal stabilities of the azoniaspiro salts, and their potential higher-temperature stable-liquid ranges, render them promising candidates for future ionic liquid applications.
Welton T, 2016, <i>Ionic Liquids in the Biorefinery Concept Challenges and Perspectives Foreword</i>, IONIC LIQUIDS IN THE BIOREFINERY CONCEPT: CHALLENGES AND PERSPECTIVES, Editors: BogelLukasik, Publisher: ROYAL SOC CHEMISTRY, Pages: VII-IX, ISBN: 978-1-84973-976-4
Welton T, 2015, Ionic Liquids and Organic Reaction Mechanisms, Ionic Liquids Completely UnCOILed: Critical Expert Overviews, Pages: 209-230, ISBN: 9781118439067
Although hundreds, perhaps thousands, of organic reactions have been reported in ionic liquids, detailed studies of their mechanisms are sparse. The following overview is a critical summary of these mechanistic studies. It will be seen that ionic liquids can have dramatic effects upon chemical reaction mechanisms, leading to changes in rates, changes in product selectivity, and even changes in the reaction occurring.
Welton T, 2015, Solvents and sustainable chemistry, Proceedings of the Royal Society A: Mathematical, Physical & Engineering Sciences, Vol: 471, ISSN: 1471-2946
Solvents are widely recognised to be of great environmental concern. The reduction of their use is one of the most important aims of green chemistry. In addition to this, the appropriate selection of solvent for a process can greatly improve the sustainability of a chemical production process. There has also been extensive research into the application of so-called green solvents, such as ionic liquids and supercritical fluids. However, most examples of solvent technologies that give improved sustainability come from the application of well-established solvents. It is also apparent that the successful implementation of environmentally sustainable processes must be accompanied by improvements in commercial performance.
Brandt A, Chen L, van Dongen BE, et al., 2015, Structural changes in lignins isolated using an acidic ionic liquid water mixture, Green Chemistry, Vol: 17, Pages: 5019-5034, ISSN: 1463-9262
Recently, acidic ionic liquid water mixtures based on the hydrogen sulfate anion have been shown to effectively extract lignin from lignocellulosic biomass. This study analyses Miscanthus giganteus lignin isolated after extraction with the protic ionic liquid 1-butylimidazolium hydrogen sulfate ([HC4im][HSO4]) followed by precipitation with the antisolvent water. Several analytical techniques were employed, such as quantitative 13C-NMR, 1H–13C HSQC NMR, 31P-NMR, Py-GC-MS, GPC and elemental analysis. The analysis shows that the ionic liquid pretreatment breaks lignin-hemicellulose linkages and depolymerizes the lignin through the cleavage of glycosidic, ester and β-O-4 ether bonds. This is accompanied by solubilization of the newly generated lignin fragments. At longer pretreatment times, repolymerization of lignin fragments through condensation reactions occurs. The isolated lignins were carbohydrate-free, had low sulfur contents, low molecular weights. Early stage lignins were structurally similar to ball-milled lignin, while more treated lignins were enriched in p-hydroxyphenyl and guaiacyl units and had a high phenolic hydroxyl group content. We conclude that, depending on the treatment conditions, lignins with a variety of characteristics can be isolated using this type of ionic liquid solution.
Prado R, Brandt A, Erdocia X, et al., 2015, Lignin oxidation and depolymerisation in ionic liquids, Green Chemistry, Vol: 18, Pages: 834-841, ISSN: 1463-9262
The depolymerisation of lignin directly in the black liquor was studied, comparing two ionic liquids as extracting solvents (butylimidazolium hydrogen sulphate and triethylammonium hydrogen sulphate), under oxidising conditions. H2O2 was chosen as the oxidant agent. It was observed that lignins derived from butylimidazolium hydrogen sulphate were more susceptible to degradation. The main degradation products found in the extracted oils were aromatic acids, such as vanillic acid, benzoic acid and 1,2-benzenedicarboxylic acid.
Eichhorn S, Rahatekar S, Welton T, et al., 2015, Revisiting regenerated cellulose fibers, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Clough M, Grasvik J, Hunt P, et al., 2015, Physicochemical investigation of ionic liquid mixtures, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
Clough M, Geyer K, Hunt P, et al., 2015, Ionic liquids: Not always innocent solvents for cellulose, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727
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