Imperial College London

Professor Tom Welton

Faculty of Natural Sciences

Dean of the Faculty of Natural Sciences
 
 
 
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Contact

 

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

 
 
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Assistant

 

Ms Mary Scott +44 (0)20 7594 5477

 
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Location

 

305Faculty BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

216 results found

Clark R, von Domaros M, McIntosh AJS, Luzar A, Kirchner B, Welton Tet al., 2019, Effect of an external electric field on the dynamics and intramolecular structures of ions in an ionic liquid., J Chem Phys, Vol: 151

Simulations of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in an external electric field have been performed using a Drude particle polarizable force field. The structure of the ions has been analyzed, with close attention paid to the configurations of the ions. The "charge arm" concept is used to explain certain changes of these configurations that would be difficult to rationalize otherwise, e.g., trans → cis isomerization of the bis(trifluoromethylsulfonyl)imide anion and extension of the alkyl chain of the cation. It has also been shown that the ions orient themselves so that their charge arms align with and stretch out along the field, and these effects occur at lower external electric field strengths than cause a change in the inherent diffusion of the ions. The dynamics of the system parallel and perpendicular to the field were analyzed, and it was found that the applied field affected the diffusion normal to the field. This is explained as a secondary effect of a change in the ion cage formed by the surrounding counterions of a given ion in the ionic liquid. The breakdown of the ion cages was rationalized by correlating changes to the inherent diffusion of the ions with other changes to the diffusion and bulk structure of the liquid, as well as considering the average forces on the ions compared to the force the ions would be expected to experience in an electric field. Parallel to the field, a drift was observed at every electric field studied. In electric fields with no changes to the ion cage structure, the relationship between the drift and electric field was found to be linear, becoming nonlinear as the ion cage structure breaks down.

Journal article

Weber CC, Brooks NJ, Castiglione F, Mauri M, Simonutti R, Mele A, Welton Tet al., 2019, On the structural origin of free volume in 1-alkyl-3-methylimidazolium ionic liquid mixtures: a SAXS and 129Xe NMR study., Physical Chemistry Chemical Physics, Vol: 21, Pages: 5999-6010, ISSN: 1463-9076

Ionic liquid (IL) mixtures enable the design of fluids with finely tuned structural and physicochemical properties for myriad applications. In order to rationally develop and design IL mixtures with the desired properties, a thorough understanding of the structural origins of their physicochemical properties and the thermodynamics of mixing needs to be developed. To elucidate the structural origins of the excess molar volume within IL mixtures containing ions with different alkyl chain lengths, 3 IL mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ILs have been explored in a joint small angle X-ray scattering (SAXS) and 129Xe NMR study. The apolar domains of the IL mixtures were shown to possess similar dimensions to the largest alkyl chain of the mixture with the size evolution determined by whether the shorter alkyl chain was able to interact with the apolar domain. 129Xe NMR results illustrated that the origin of excess molar volume in these mixtures was due to fluctuations within these apolar domains arising from alkyl chain mismatch, with the formation of a greater number of smaller voids within the IL structure. These results indicate that free volume effects for these types of mixtures can be predicted from simple considerations of IL structure and that the structural basis for the formation of excess molar volume in these mixtures is substantially different to IL mixtures formed of different types of ions.

Journal article

Gehrke S, Reckien W, Palazzo I, Welton T, Hollóczki Oet al., 2019, On the Carbene-Like Reactions of Imidazolium Acetate Ionic Liquids: Can Theory and Experiments Agree?, European Journal of Organic Chemistry, Vol: 2019, Pages: 504-511, ISSN: 1434-193X

© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The N-heterocyclic carbene organocatalytic reactivity of the 1-ethyl-3-methylimidazolium acetate ionic liquid was investigated on the model reaction between this solvent and anisaldehyde. The formation of carbenes by a proton transfer from the cation to the anion was compared to a direct reaction mechanism, in which the proton transfer and the C–C bond formation between catalyst and substrate occurs in a single elementary step. Interestingly, the two reaction mechanisms show a much smaller difference in activation energies than those observed for analogous catalytic systems with neutral bases, showing that the mechanism might switch from one to the other at different temperatures or with different substrates. In this particular case, however, the direct reaction mechanism, avoiding free carbenes in the solution, is apparently more feasible. Based on the detailed analysis of this reaction path, the earlier contradictions between theory and experiments can be resolved, resulting in a consistent mechanistic picture for the related processes. Additionally, we show on the example of a platinum surface that introducing metal probes into the liquid may induce carbene-like reactions, as the formation of a strong coordinative bond between the carbene and a platinum atom at the surface is highly exothermic, shifting the acid-base equilibrium considerably.

Journal article

Welton T, 2018, Editorial Overview: UN Sustainable Development Goals: How can sustainable/green chemistry contribute? There can be more than one approach, Current Opinion in Green and Sustainable Chemistry, Vol: 13, Pages: A7-A9, ISSN: 2452-2236

Journal article

Welton T, 2018, Ionic liquids: a brief history., Biophysical Reviews, Vol: 10, Pages: 691-706, ISSN: 1867-2450

There is no doubt that ionic liquids have become a major subject of study for modern chemistry. We have become used to ever more publications in the field each year, although there is some evidence that this is beginning to plateau at approximately 3500 papers each year. They have been the subject of several major reviews and books, dealing with different applications and aspects of their behaviours. In this article, I will show a little of how interest in ionic liquids grew and developed.

Journal article

Welton T, 2018, Ken Seddon-obituary., Biophys Rev, Vol: 10, ISSN: 1867-2450

Journal article

Vincent S, Prado R, Kuzmina O, Potter K, Bhardwaj J, Wanasekara ND, Harniman RL, Koutsomitopoulou A, Eichhorn SJ, Welton T, Rahatekar SSet al., 2018, Regenerated cellulose and willow lignin blends as potential renewable precursors for carbon fibers, ACS Sustainable Chemistry and Engineering, Vol: 6, Pages: 5903-5910, ISSN: 2168-0485

We report on the extraction of lignin from willow and its use to manufacture cellulose-lignin fibers as potential precursors for the manufacture of carbon fibers. The lignin from willow was extracted using triethylammonium hydrogen sulfate [Et3NH][HSO4]. The lignin extracted by this process was characterized by ATR-IR and elemental analysis, which indicated a high carbon yield. 1-Ethyl-3-methylimidazolium acetate [C2C1im][OAc] was then used as a common solvent to dissolve cellulose and lignin to manufacture lignin-cellulose fiber blends. The Young’s modulus of a 75:25 lignin/cellulose fiber was found to be 3.0 ± 0.5 GPa, which increased to 5.9 ± 0.6 GPa for a 25:75 lignin/cellulose blend. From a characterization of the surface morphology, using scanning electron microscopy (SEM) and atomic force microscopy (AFM), it was observed that higher lignin content in the fiber blend increased the surface roughness. FT-IR analysis confirmed the presence of aromatic groups related to lignin in the obtained fibers from the presence of peaks located at ∼1505 cm–1 and ∼1607 cm–1. The presence of lignin improves the thermal stability of the fiber blends by allowing them to degrade over a wider temperature range. The presence of lignin also improved the carbon yield during carbonization. Therefore, the lignin-cellulose fibers developed in this work can offer an excellent alternative to pure cellulose or lignin filaments.

Journal article

Bastos JC, Carvalho SF, Welton T, Canongia Lopes JN, Rebelo LPN, Shimizu K, Araujo JMM, Pereiro ABet al., 2018, Design of task-specific fluorinated ionic liquids: nanosegregation versus hydrogen-bonding ability in aqueous solutions, Chemical Communications, Vol: 54, Pages: 3524-3527, ISSN: 1359-7345

We demonstrate that fluorinated ionic liquids reduce the impact of the addition of water upon the ionic liquid's H-bond acceptance ability. This is a key factor to obtain functionalized materials to be used e.g. in the dissolution of biomolecules, extraction processes or material engineering.

Journal article

Clark R, Edel J, Kirchner B, Kuimova M, McIntosh A, Nawawi M, von Domaros M, Welton Tet al., 2018, Ion diffusion in ionic liquids in electric fields, 255th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nexus of Food, Energy, and Water, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727

Conference paper

Holbrey J, Welton T, 2018, Obituary: Kenneth R. Seddon: 1950-2018, GREEN CHEMISTRY, Vol: 20, Pages: 776-776, ISSN: 1463-9262

Journal article

Gehrke S, von Domaros M, Clark R, Holloczki O, Brehm M, Welton T, Luzar A, Kirchner Bet al., 2018, Structure and lifetimes in ionic liquids and their mixtures, FARADAY DISCUSSIONS, Vol: 206, Pages: 219-245, ISSN: 1359-6640

Journal article

Florindo C, McIntosh AJS, Welton T, Branco LC, Marrucho IMet al., 2017, A closer look into deep eutectic solvents: exploring intermolecular interactions using solvatochromic probes., Physical Chemistry Chemical Physics, Vol: 20, Pages: 206-213, ISSN: 1463-9076

Deep eutectic solvents (DESs) constitute a new class of ionic solvents that has been developing at a fast pace in recent years. Since these solvents are commonly suggested as green alternatives to organic solvents, it is important to understand their physical properties. In particular, polarity plays an important role in solvation phenomena. In this work, the polarity of different families of DESs was studied through solvatochromic responses of UV-vis absorption probes. Kamlet-Taft α, β, π* and ETN parameters were evaluated using different solvatochromic probes, as 2,6-dichloro-4-(2,4,6-triphenyl-N-pyridino)-phenolate (Reichardt's betaine dye 33), 4-nitroaniline, and N,N-diethyl-4-nitroaniline for several families of DESs based on cholinium chloride, dl-menthol and a quaternary ammonium salt ([N4444]Cl). In addition, a study to understand the difference in polarity properties between DESs and the corresponding ILs, namely ILs based on cholinium cation and carboxylic acids as anions ([Ch][Lev], [Ch][Gly] and [Ch][Mal]), was carried out. The chemical structure of the hydrogen bond acceptor (HBA) in a DES clearly controls the dipolarity/polarizability afforded by the DES. Moreover, Kamlet-Taft parameters do not vary much within the family, but they differ among families based on different HBA, either for DESs containing salts ([Ch]Cl or [N4444]Cl) or neutral compounds (dl-menthol). A substitution of the HBD was also found to play an important role in solvatochromic probe behaviour for all the studied systems.

Journal article

Kuzmina O, Bhardwaj J, Vincent SR, Wanasekara ND, Kalossaka LM, Griffith J, Potthast A, Rahatekar S, Eichhorn SJ, Welton Tet al., 2017, Superbase ionic liquids for effective cellulose processing from dissolution to carbonisation, Green Chemistry, Vol: 19, Pages: 5949-5957, ISSN: 1463-9262

A range of superbase derived ionic liquids (SILs) was synthesised and characterised. Their ability to dissolve cellulose and the characteristics of the produced fibres were correlated to their specific structural and solvent properties. 17 ionic liquids (ILs) (including 9 novel) were analysed and six ILs were selected to produce fibres: 1-ethyl-3-methylimidazolium acetate [C2C1im][OAc], 1-ethyl-3-methylimidazolium diethyl phosphate [C2C1im][DEP] and the SILs 1-ethyl-1,8-diazabicyclo[5.4.0]undec-7-enium diethylphosphate [DBUEt][DEP], 1,8-diazabicyclo[5.4.0]undec-7-enium acetate [DBUH][OAc], 1,5-diazabicyclo[4.3.0]non-5-enium acetate [DBNH][OAc] and 1-ethyl-1,5-diazabicyclo[4.3.0]non-5-enium diethylphsophate [DBNEt][DEP]. The mechanical properties of these fibres were investigated. The obtained fibres were then carbonised to explore possible application as carbon fibre precursors. The fibres obtained using a mixture of 1,5-diazabicyclo[4.3.0]non-5-enium based SILs with acetate and hexanoate anions (9 : 1), [DBNH][OAc][Hex], showed a promising combination of strength, stiffness and strain at failure values for applications in textiles and fibre reinforcement in renewable composites. Using Raman spectroscopy it is demonstrated that these fibres exhibit a relatively high degree of structural order, with fewer defects than the other materials. On the other hand, analogous fibres based on imidazolium cation with acetate and hexanoate anions (9 : 1), [C2C1im][OAc][Hex] showed a decline in the quality of the produced fibres compared to the fibres produced from [C2C1im][OAc], [C2C1im][DEP] or [DBNH][OAc][Hex].

Journal article

Hallett J, Welton T, Brandt-Talbot A, 2017, Treatment, EP3244371 (A1)

The present disclosure relates to an improved method for treating a lignocellulose biomass in order to dissolve the lignin therein, while the cellulose does not dissolve. The cellulose pulp obtained can be used to produce glucose. In addition the lignin can be isolated for subsequent use in the renewable chemical industry.

Patent

Daud NMAN, Bakis E, Hallett JP, Weber CC, Welton Tet al., 2017, Evidence for the spontaneous formation of N-heterocyclic carbenes in imidazolium based ionic liquids, Chemical Communications, Vol: 53, Pages: 11154-11156, ISSN: 1359-7345

We present a study of the reactions of aldehydes in ionic liquids which gives evidence for the spontaneous formation of N-heterocyclic carbenes in ionic liquids based on 1,3-dialkyl substituted imidazolium cations from the lack of a deuterium isotope effect on the reaction of these ionic liquids with aldehydes.

Journal article

Kuzmina O, Symianakis E, Godfrey D, Albrecht T, Welton Tet al., 2017, Ionic liquids for metal extraction from chalcopyrite: solid, liquid and gas phase studies, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 19, Pages: 21556-21564, ISSN: 1463-9076

Journal article

Kuzmina O, Hassan NH, Patel L, Ashworth C, Bakis E, White AJP, Hunt PA, Welton Tet al., 2017, The impact of ionic liquids on the coordination of anions with solvatochromic copper complexes, Dalton Transactions, Vol: 46, Pages: 12185-12200, ISSN: 1477-9234

Solvatochromic transition metal (TM)-complexes with weakly associating counter-anions are often used to evaluate traditional neutral solvent and anion coordination ability. However, when employed in ionic liquids (IL) many of the common assumptions made are no longer reliable. This study investigates the coordinating ability of weakly coordinating IL anions in traditional solvents and within IL solvents employing a range of solvatochromic copper complexes. Complexes of the form [Cu(acac)(tmen)][X] (acac = acetylacetonate, tmen = tetramethylethylenediamine) where [X]− = [ClO4]−, Cl−, [NO3]−, [SCN]−, [OTf]−, [NTf2]− and [PF6]− have been synthesised and characterised both experimentally and computationally. ILs based on these anions and imidazolium and pyrrolidinium cations, some of which are functionalised with hydroxyl and nitrile groups, have been examined. IL-anion coordination has been investigated and compared to typical weakly coordinating anions. We have found there is potential for competition at the Cu-centre and cases of anions traditionally assigned as weakly associating that demonstrate a stronger than expected level of coordinating ability within ILs. [Cu(acac)(tmen)][PF6] is shown to contain the least coordinating anion and is established as the most sensitive probe studied here. Using this probe, the donor numbers (DNs) of ILs have been determined. Relative donor ability is further confirmed based on the UV-Vis of a neutral complex, [Cu(sacsac)2] (sacsac = dithioacetylacetone), and DNs evaluated via23Na NMR spectroscopy. We demonstrate that ILs can span a wide donor range, similar in breadth to conventional solvents.

Journal article

Brooks NJ, Castiglione F, Doherty CM, Dolan A, Hill AJ, Hunt PA, Matthews RP, Mauri M, Mele A, Simonutti R, Villar-Garcia IJ, Weber CC, Welton Tet al., 2017, Linking the structures, free volumes, and properties of ionic liquid mixtures, Chemical Science, Vol: 8, Pages: 6359-6374, ISSN: 2041-6520

The formation of ionic liquid (IL) mixtures has been proposed as an approach to rationally fine-tune the physicochemical properties of ILs for a variety of applications. However, the effects of forming such mixtures on the resultant properties of the liquids are only beginning to be understood. Towards a more complete understanding of both the thermodynamics of mixing ILs and the effect of mixing these liquids on their structures and physicochemical properties, the spatial arrangement and free volume of IL mixtures containing the common [C4C1im]+ cation and different anions have been systematically explored using small angle X-ray scattering (SAXS), positron annihilation lifetime spectroscopy (PALS) and 129Xe NMR techniques. Anion size has the greatest effect on the spatial arrangement of the ILs and their mixtures in terms of the size of the non-polar domains and inter-ion distances. It was found that differences in coulombic attraction between oppositely charged ions arising from the distribution of charge density amongst the atoms of the anion also significantly influences these inter-ion distances. PALS and 129Xe NMR results pertaining to the free volume of these mixtures were found to strongly correlate with each other despite the vastly different timescales of these techniques. Furthermore, the excess free volumes calculated from each of these measurements were in excellent agreement with the excess volumes of mixing measured for the IL mixtures investigated. The correspondence of these techniques indicates that the static and dynamic free volume of these liquid mixtures are strongly linked. Consequently, fluxional processes such as hydrogen bonding do not significantly contribute to the free volumes of these liquids compared to the spatial arrangement of ions arising from their size, shape and coulombic attraction. Given the relationship between free volume and transport properties such as viscosity and conductivity, these results provide a link between the s

Journal article

Poulos AS, Griffith J, Mcqueen L, Welton T, Brooks N, Ces Oet al., 2017, Model phospholipid self-assembly in ionic liquids and deep eutectic solvents, 19th IUPAB Congress / 11th EBSA Congress, Publisher: SPRINGER, Pages: S363-S363, ISSN: 0175-7571

Conference paper

Mahmood H, Moniruzzaman M, Yusup S, Welton Tet al., 2017, Ionic Liquids Assisted Processing of Renewable Resources for the Fabrication of Biodegradable Composite Materials, Green Chemistry, Vol: 19, Pages: 2051-2075, ISSN: 1744-1560

In recent years, the utilization of renewable resources, particularly lignocellulosic biomass based raw materials, to replace synthetic materials/polymers for the manufacture of green materials has gained increased worldwide interest due to growing global environmental awareness, concepts of sustainability and the absence of conflict between food and chemical/materials production. However, structural heterogeneity and the presence of networks of inter- and intra-molecular interactions in biopolymer matrices remain unsolved challenges to clean pretreatment for biocomposite processing. A number of techniques including physical, physico-chemical and chemical methods have been investigated for the pretreatment of renewable resources. Most of these methods require high temperatures and pressures, as well as highly concentrated chemicals for the pretreatment process. Fortunately, ionic liquids (ILs) – potentially attractive “green” recyclable alternatives to environmentally harmful organic solvents – have been increasingly exploited as solvents and/or (co)solvents and/or reagents for biopolymer processing. Compared to conventional approaches, ILs in processing biodegradable composites exhibit many advantages such as being noncorrosive and nonvolatile, having excellent dissolution power under relatively mild conditions and high thermal stability. Presently, a wide range of different approaches have been explored to further improve the performance of ILs processing of biobased polymers for composites manufacturing. The main goal of this review is to present recent technological developments in which the advantages of ILs as processing solvents for biopolymers for the production of a plethora of green composites have been gradually realized. It is hoped that the present article will inspire new ideas and new approaches in ILs-assisted processing of renewable resources for green composite production.

Journal article

Weigand L, Mostame S, Brandt-Talbot A, Welton T, Hallett JPet al., 2017, Effect of pretreatment severity on the cellulose and lignin isolated from Salix using ionoSolv pretreatment, Faraday Discussions, Vol: 202, Pages: 331-349, ISSN: 1359-6640

The ionoSolv pretreatment is a new technique employing protic low-cost ionic liquids and has previously been applied to successfully fractionate switchgrass and the grass Miscanthus giganteus. This study investigates the effect of using the protic ionic liquid solution [N2220][HSO4]80% with two different acid/base ratios (1.02 and 0.98) at 120, 150 and 170 °C on the pretreatment outcome of the hardwood willow. The ionic liquid solution was able to fractionate willow, and a pulp and lignin fraction were recovered after treatment. The pretreatment success was determined via enzymatic hydrolysis of the pulp, which showed that the ionoSolv pretreatment was able to increase enzymatic glucose yields compared to untreated willow biomass. The pretreatment produced a cellulose-rich pulp with high hemicellulose and lignin removal. The pulp composition and glucose yield after saccharification were greatly influenced by the acidity of the ionic liquid solution, temperature and pretreatment time. The extracted lignin was analysed via 2-D HSQC NMR spectroscopy and GPC to investigate the changes in the lignin structure induced by the pretreatment severity. The lignin structure (in terms of inter-unit linkages and S/G ratio) and molecular weight varied significantly depending on the pretreatment conditions used.

Journal article

Prado R, Weigand L, Zahari SMSNS, Erdocia X, Hallett JP, Labidi J, Welton Tet al., 2017, An easy and reliable method for syringyl:guaiacyl ratio measurement, TAPPI JOURNAL, Vol: 16, Pages: 145-152, ISSN: 0734-1415

Journal article

Prado R, Weigand L, Zahari SMSNS, Erdocia X, Hallett JP, Labidi J, Welton Tet al., 2017, An easy and reliable method for syringyl: guaiacyl ratio measurement, TAPPI JOURNAL, Vol: 16, Pages: 145-152, ISSN: 0734-1415

Journal article

Tome LC, Gouveia ASL, Ab Ranii MA, Lickiss PD, Welton T, Marrucho IMet al., 2017, Study on Gas Permeation and CO2 Separation through Ionic Liquid Based Membranes with Siloxane-Functionalized Cations, Industrial & Engineering Chemistry Research, Vol: 56, Pages: 2229-2239, ISSN: 0888-5885

This work explores ionic liquid-based membranes with siloxane functionalized cations using two different approaches: supported ionic liquid membranes (SILMs) and poly(ionic liquid)–ionic liquid (PIL–IL) composite membranes. Their CO2, CH4, and N2 permeation properties were measured at T = 293 K with a trans-membrane pressure differential of 100 kPa. The thermophysical properties of the synthesized siloxane-functionalized ILs, namely viscosity and density (data in the Supporting Information), were also determined. Contrary to what was expected, the gas permeation results show that the SILMs containing siloxane-functionalized cations have CO2 permeabilities that are lower than those of their analogues without the siloxane functionality. The addition of siloxane-based ILs into PILs increases both CO2 permeability and CO2/N2 permselectivity, although it does not significantly change the CO2/CH4 permselectivity. The prepared membranes present very diverse CO2 permeabilities, between 57 and 568 Barrer, while they show permselectivities varying from 16.8 to 36.8 for CO2/N2 and from 9.8 to 11.5 for CO2/CH4. As observed for other ILs, superior CO2 separation performances were obtained when the IL containing [C(CN)3]− is used compared to that having the [NTf2]− anion.

Journal article

De Gregorio GF, Weber CC, Gräsvik J, Welton T, Brandt A, Hallett JPet 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.

Journal article

De Gregorio GF, Prado R, Vriamont C, Erdocia X, Labidi J, Hallett JP, Welton Tet 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.

Journal article

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

Journal article

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

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