Imperial College London

Professor Tom Welton

Faculty of Natural SciencesDepartment of Chemistry

Professor of Sustainable Chemistry
 
 
 
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Contact

 

+44 (0)20 7594 5763t.welton Website

 
 
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Location

 

601AMolecular Sciences Research HubWhite City Campus

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Summary

 

Publications

Publication Type
Year
to

219 results found

Hunt PA, Ashworth C, Matthews R, Welton Tet 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.

Journal article

Hunt PA, Welton T, Hallett J, Schmauck J, Bordes E, Kuzmina Oet 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.

Journal article

Prado R, Erdocia X, De Gregorio GF, Labidi J, Welton Tet 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.

Journal article

Saugar AI, Marquez-Alvarez C, Villar-Garcia IJ, Welton T, Perez-Pariente Jet 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

Journal article

Eyckens DJ, Demir B, Walsh TR, Welton T, Henderson LCet 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).

Journal article

Albrecht T, Godfrey D, Bannock JH, Kuzmina O, Welton Tet 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.

Journal article

Welton T, Griffith J, Clough M, Kuzmina Oet 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.

Journal article

Prado R, Brandt A, Erdocia X, Hallett J, Labidi J, Welton Tet al., 2016, Depolymerisation of lignin by oxidation in ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Vincent SR, Prado R, Koutsomitopoulou A, Potter K, Eichhorn S, Kuzmina O, Welton T, Rahatekar Set al., 2016, Fibre spinning of lingo-cellulose biomass using ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Kuzmina O, Welton T, 2016, Physicochemical properties of cellulose-dissolving superbase ionic liquids, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Rahatekar S, Zhu C, Eichhorn S, Wanasekara N, Kuzmina O, Welton T, Potter Ket al., 2016, Manufacturing strong regenerated cellulose nano-composite fibres, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Welton T, Edel J, McIntosh A, 2016, Ion diffusion in ionic liquids: Single molecule fluorescence spectroscopy, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Wanasekara N, Zhu C, Eichhorn S, Rahatekar S, Welton T, Bismarck A, Potter Ket al., 2016, Molecular deformation in high performance cellulose fibres, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Welton T, Matthews RP, Villar-Garcia IJ, Weber CC, Griffith J, Cameron F, Hallett JP, Hunt PAet 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.

Journal article

Welton T, 2016, Much to be proud of, Chemical & Engineering News, Vol: 94, Pages: 3-3, ISSN: 1520-605X

Journal article

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

Journal article

Eyckens DJ, Champion ME, Fox BL, Yoganantharajah P, Gibert Y, Welton T, Henderson LCet 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.

Journal article

Clough MT, Geyer K, Hunt PA, McIntosh AJ, Rowe R, Welton T, White AJet 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.

Journal article

Welton T, 2016, Foreword, ISBN: 9781849739795

Book

Welton T, 2015, Ionic Liquids and Organic Reaction Mechanisms, Ionic Liquids Completely UnCOILed: Critical Expert Overviews, Pages: 209-230, ISBN: 9781118439067

© 2015 by John Wiley & Sons, Inc. All rights reserved. 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.

Book chapter

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.

Journal article

Prado R, Brandt A, Erdocia X, Hallet J, Welton T, Labidi Jet 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.

Journal article

Eichhorn S, Rahatekar S, Welton T, Potter K, Bismarck A, Wanasekara Net al., 2015, Revisiting regenerated cellulose fibers, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Clough M, Grasvik J, Hunt P, Niedermeyer H, Welton Tet al., 2015, Physicochemical investigation of ionic liquid mixtures, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Clough M, Geyer K, Hunt P, Son S, Vagt U, Welton Tet al., 2015, Ionic liquids: Not always innocent solvents for cellulose, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Matthews RP, Welton T, Hunt PA, 2015, Hydrogen bonding and pi-pi interactions in imidazolium-chloride ionic liquid clusters, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 17, Pages: 14437-14453, ISSN: 1463-9076

Journal article

Brandt A, Chen L, van Dongen BE, Welton T, Hallett JPet al., 2015, Structural changes in lignins isolated using an acidic ionic liquid water mixture, GREEN CHEMISTRY, Vol: 17, Pages: 5019-5034, ISSN: 1463-9262

Journal article

George A, Brandt A, Tran K, Zahari SMSNS, Klein-Marcuschamer D, Sun N, Sathitsuksanoh N, Shi J, Stavila V, Parthasarathi R, Singh S, Holmes BM, Welton T, Simmons BA, Hallett JPet al., 2014, Design of low-cost ionic liquids for lignocellulosic biomass pretreatment, Green Chemistry, Vol: 17, Pages: 1728-1734, ISSN: 1744-1560

The cost of ionic liquids (ILs) is one of the main impediments to IL utilization in the cellulosic biorefinery, especially in the pretreatment step. In this study, a number of ionic liquids were synthesized with the goal of optimizing solvent cost and stability whilst demonstrating promising processing potential. To achieve this, inexpensive feedstocks such as sulfuric acid and simple amines were combined into a range of protic ionic liquids containing the hydrogen sulfate [HSO4]− anion. The performance of these ionic liquids was compared to a benchmark system containing the IL 1-ethyl-3-methylimidazolium acetate [C2C1im][OAc]. The highest saccharification yields were observed for the triethylammonium hydrogen sulfate IL, which was 75% as effective as the benchmark system. Techno-economic modeling revealed that this promising and yet to be optimized yield was achieved at a fraction of the processing cost. This study demonstrates that some ILs can compete with the cheapest pretreatment chemicals, such as ammonia, in terms of effectiveness and process cost, removing IL cost as a barrier to the economic viability of IL-based biorefineries.

Journal article

Clough MT, Crick CR, Grasvik J, Hunt PA, Niedermeyer H, Welton T, Whitaker OPet al., 2014, A physicochemical investigation of ionic liquid mixtures, Chemical Science, Vol: 6, Pages: 1101-1114, ISSN: 2041-6539

Ionic liquids have earned the reputation of being ‘designer solvents’ due to the wide range of accessible properties and the degree of fine-tuning afforded by varying the constituent ions. Mixtures of ionic liquids offer the opportunity for further fine-tuning of properties. A broad selection of common ionic liquid cations and anions are employed to create a sample of binary and reciprocal binary ionic liquid mixtures, which are analysed and described in this paper. Physical properties such as the conductivity, viscosity, density and phase behaviour (glass transition temperatures) are examined. In addition, thermal stabilities of the mixtures are evaluated. The physical properties examined for these formulations are found to generally adhere remarkably closely to ideal mixing laws, with a few consistent exceptions, allowing for the facile prediction and control of properties of ionic liquid mixtures.

Journal article

Clough MT, Geyer K, Hunt PA, Son S, Vagt U, Welton Tet al., 2014, Ionic liquids: not always innocent solvents for cellulose, Green Chemistry, Vol: 17, Pages: 231-243, ISSN: 1744-1560

The decomposition pathways of a series of carbohydrates dissolved in carboxylate ionic liquids have been investigated in detail using a broad range of thermal and chromatographic techniques. Mixtures of the carboxylate ionic liquid 1-ethyl-3-methylimidazolium acetate with carbohydrates were found to undergo reaction of the C2 carbon of the imidazolium ring with the aldehyde functionality on the open chain sugar, yielding an imidazolium adduct with a hydroxylated alkyl chain. Subsequently, degradation of the hydroxyalkyl chain occurs by sequential loss of formaldehyde units, to yield a terminal adduct species, 1-ethyl-2-(hydroxymethyl)-3-methylimidazolium acetate. Identities of the final and intermediate adduct species, and the reaction mechanisms connecting adducts, were elucidated by NMR, HPLC and LCMS techniques. Factors affecting the rate and quantity of adduct formation were explored. Changing the ionic liquid cation and anion, the acid number, sugar concentration and temperature influenced the rate of formation and relative quantities of the adduct species. Formation of adducts could not be entirely prevented when employing carboxylate ionic liquids. By contrast, 1-butyl-3-methylimidazolium chloride was identified as an ionic liquid capable of dissolving a significant quantity of cellulose, yet without reacting with carbohydrates.

Journal article

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