Tetraalkylphosphonium Ionic Liquids Research Articles

Non-Isochronal Behavior of Charge Transport at Liquid-Liquid and Liquid-Glass Transition in Aprotic Ionic Liquids.

A reversible, first-order transition separating two liquid phases of a single-component material is a fascinating yet poorly understood phenomenon. Here, we investigate the liquid-liquid transition (LLT) ability of two tetraalkylphosphonium ionic liquids (ILs), [P666,14]Cl and [P666,14][1,2,4-triazolide], using differential scanning calorimetry and dielectric spectroscopy. The latter technique also allowed us to study the LLT at elevated pressure. We found that cooling below 205 K transforms [P666,14]Cl and [P666,14][Trz] from one liquid state (liquid 1) to another (the self-assembled liquid 2), while the latter facilitates the charge transport decoupled from structural dynamics. In contrast to temperature, pressure was found to play an essential role in the self-organization of a liquid 2 phase, resulting in different time scales of charge transport for rapidly and slowly compressed samples. Furthermore, τσ(PLL) was found to be much shorter than τσ(TLL, P=atm), which constitutes the first example of non-isochronal behavior of charge transport at LLT. In turn, dielectric studies through the liquid-glass transition revealed the non-monotonic behavior of τσ at elevated pressure for [P666,14]Cl, while for [P666,14][Trz] τσ(Pg) was almost constant. These results highlight the diversity of liquid-liquid transition features within the class of phosphonium ionic liquids.

Tailoring Phosphonium Ionic Liquids for a Liquid-Liquid Phase Transition.

The existence of more than one liquid state in a single-component system remains the most intriguing physical phenomenon. Herein, we explore the effect of cation self-assembly on ion dynamics in the vicinity of liquid-liquid and liquid-glass transition of tetraalkyl phosphonium ([Pmmm,n]+, m = 4, 6; n = 2-14) ionic liquids. We found that nonpolar local domains formed by 14-carbon alkyl chains are crucial in obtaining two supercooled states of different dynamics within a single ionic liquid. Although the nano-ordering, confirmed by Raman spectroscopy, still occurs for shorter alkyl chains (m = 6, n < 14), it does not bring calorimetric evidence of LLT. Instead, it results in peculiar behavior of ion dynamics near the liquid-glass transition and 20-times smaller size of the dynamic heterogeneity compared to imidazolium ionic liquids. These results represent a crucial step toward understanding the nature of the LLT phenomenon and offer insight into the design of efficient electrolytes based on ionic liquids revealing self-assembly behavior.

Solubility of Water in Aprotic Heterocyclic Anion (AHA) Ionic Liquids

The hydrophobic–hydrophilic character of a series of 15 tetra-alkylphosphonium ionic liquids with aprotic heterocyclic anions (AHAs) was studied by measuring their liquid–liquid equilibrium with wa...

Diffusional Dynamics of Tetraalkylphosphonium Ionic Liquid Films Measured by Fluorescence Correlation Spectroscopy.

Fluorescence correlation spectroscopy (FCS) is applied to investigate the diffusional dynamics of hydrophilic (Atto 590) and amphiphilic (DiD) fluorophores in a series of alkylphosphonium ionic liquid (IL) films ([P4448][Cl], [P6668][Cl], [P66614][Cl], and [P66614][NTf2]) in order to determine diffusional parameters and to elucidate nanoscale structural heterogeneities within the IL. From the measured correlation functions, the diffusion coefficients of the fluorescent molecules are estimated, rendering values that span from 0.39 to 1.2 and 0.146 to 5.2 μm2/s for Atto 590 and DiD, respectively. An increase in the diffusion coefficient values is correlated to the increase in the alkyl chain length, which in turn is correlated with a decrease in their viscosity. Interestingly, deviations from Brownian diffusion behavior of the fluorescent probes in the ILs are observed, showing a time-dependent diffusion coefficient in most of the cases. These deviations can be attributed to the presence of nanoscale structural heterogeneities in the tetraalkylphosphonium ILs. These results experimentally confirm the presence of nanosegregation in tetraalkylphosphonium ILs, which has been previously observed in molecular dynamics studies.

Molecular insights into ionic liquid/aqueous interface of phosphonium based phase-separable ionic liquids

Phosphonium based phase-separable ionic liquids (PSILs) are promising green solvents for dissolution of cellulose and lignin, a necessary step for conversion of biomass to fuels and chemicals. The knowledge of interfacial behavior of ionic liquid/solvent systems is critical for designing efficient separation processes. Here, molecular dynamics simulations are carried out for aqueous interface of tetraalkylphosphonium ionic liquids with chloride and acetate as anions to investigate IL miscibility with water. The transition zone from miscible to immiscible behavior was observed for alkyl chain lengths of 6 to 8. Emulsion phase was observed for [P8888]+ ion and multiple IL/water interface was observed for [P12121212]+ phosphonium cation. IL/water interface is observed to be enriched with solvated anions with phosphorous atom oriented towards the aqueous phase. The potential of mean force calculations suggest that as the alkyl chain of the phosphonium cations increase, so does the driving force for aggregation of cations in the aqueous phase. Due to the difference in the molecular shape and size, anions are better solvated by the water molecules, and these ions diffuse into the aqueous phase. Furthermore, the analysis of selected pair interactions provides insights into the nature of intermolecular forces and the role of the alkyl side chains on the interfacial properties.

Vaporization thermodynamics of ionic liquids with tetraalkylphosphonium cations

Vapour pressures and vaporization enthalpies of tetraalkylphosphonium ionic liquids with [PF6]−, [NTf2]−, Cl−, and Br− anions have been measured by using quartz-crystal microbalance and thermogravimetry. Chain-length dependences of the vaporization enthalpies have been established and used for validation of experimental data. Quantification of Coulomb and dispersion forces was performed by comparison with vaporization enthalpies of alkanes and trialkylphosphines.

Absorption of n-butane in imidazolium and phosphonium ionic liquids and application to separation of hydrocarbon gases

In this report, the density, viscosity, and heat capacity of the tetraalkylphosphonium ionic liquids, containing newly synthesized trihexyltetradecylphosphonium p-dodecylbenzenesulfonate and bis(2-ethylhexyl)sulfobutanedioate, were measured at atmospheric pressure. Then, the n-butane absorption in the dialkylimidazolium and tetraalkylphosphonium ionic liquids were investigated at the n-butane pressure of 0.101 MPa and the temperatures of (298.15–353.15) K. In a series of bis(trifluoromethanesulfonyl)amide ionic liquids, the trihexyltetradecylphosphonium salt absorbed the largest amount of n-butane, followed by the triethyloctylphosphonium, 1-methyl-3-octylimidazolium, and 1-butyl-3-methylimidazolium salts. On the other hand, in the trihexyltetradecylphosphonium ionic liquids, the bis(2-ethylhexyl)sulfobutanedioate and p-dodecylbenzenesulfonate salts had the higher solubilities of n-butane than the bis(trifluoromethanesulfonyl)amide salt. In addition, the solubilities of water vapor in the trihexyltetradecylphosphonium salt were measured at 298.2 K and atmospheric pressure. Trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)amide was the most free from the moisture. We further performed the continuous gas absorption experiments of n-heptane and toluene using the present tetraalkylphosphonium ionic liquids. They removed successfully the vapors of hydrocarbons despite the very dilute concentrations of hydrocarbons, less than 1500 ppm. The initial absorption rates were calculated to discuss the absorption kinetics in the tetraalkylphosphonium ionic liquids.

Synthesis, characterization, and evaluation of iron nanoparticles as hydrogenation catalysts in alcohols and tetraalkylphosphonium ionic liquids: do solvents matter?

Best recyclability seen for Fe nanoparticles in alcohol solvents in which Fe-core, Fe oxide shell nanoparticles are formed.

Viscosity of Ionic Liquid–Ionic Liquid Mixtures

The viscosities of 23 ionic liquid (IL)–IL mixtures were measured at multiple temperatures and mole fractions. Many of the mixtures involved a dialkylimidazolium bis(trifluoromethylsulfonyl)imide ([Tf2N]) IL paired with a tetra-alkylphosphonium IL containing an aprotic heterocyclic anion (AHA). As a result, most of the mixtures contained both unlike anions and cations. The mixtures ranged from strongly positive deviations from the Arrhenius model (the mole fraction weighted logarithm of the viscosity), even having mixture viscosities greater than the viscosity of either pure IL, to negative deviations. Studies of complementary pairs ([C1][A1] + [C2][A2] and [C2][A1] + [C1][A2] mixtures) have identical viscosities at overall mole fractions of 0.50, clearly indicating that the anions and cations of the mixtures exchange freely. These mixtures cannot be well-represented by the Arrhenius model assuming a random distribution of the four possible cation/anion combinations (e.g., 0.25 mole fraction of each possi...

Fe(III) recovery from HCl solutions using amberlite XAD‐7 resin impregnated with a tetraalkyl phosphonium ionic liquid

AbstractFe(III) is efficiently extracted from concentrated HCl solutions using Amberlite XAD‐7 impregnated with tetraalkyl phosphonium chloride ionic liquid (IL) (synthesis of extractant‐impregnated resin, EIR). The sorption efficiency is controlled by metal speciation and IL loading in the EIR. Sorption isotherms in mono‐component solutions are described by the Langmuir equation, while the extended Langmuir equation perfectly fits sorption isotherms from binary Fe(III)/Zn(II) solutions. The thermodynamic study confirms the endothermic nature of the sorption. Uptake kinetics are fitted by the pseudo‐second order rate equation. While temperature and metal concentration have a relatively limited effect on kinetics, the IL content more significantly affects the mass transfer of Fe(III). Water, sodium sulphate, nitric acid, and sulphuric acid almost completely desorb Fe(III) from loaded EIRs. Resin recycling was tested for eight cycles without significant decrease of the sorption and desorption efficiencies.

Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid.

A new low-energy pathway is reported for the electrochemical reduction of CO2 to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P66614][124Triz] is able to chemisorb CO2 through equimolar binding of CO2 with the 1,2,4-triazole anion. This chemisorbed CO2 can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO2 within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P66614][NTf2]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.

Reduction of Carbon Dioxide to Formate at Low Overpotential Using a Superbase Ionic Liquid

AbstractA new low‐energy pathway is reported for the electrochemical reduction of CO2 to formate and syngas at low overpotentials, utilizing a reactive ionic liquid as the solvent. The superbasic tetraalkyl phosphonium ionic liquid [P66614][124Triz] is able to chemisorb CO2 through equimolar binding of CO2 with the 1,2,4‐triazole anion. This chemisorbed CO2 can be reduced at silver electrodes at overpotentials as low as 0.17 V, forming formate. In contrast, physically absorbed CO2 within the same ionic liquid or in ionic liquids where chemisorption is impossible (such as [P66614][NTf2]) undergoes reduction at significantly increased overpotentials, producing only CO as the product.

Optimization of transition metal nanoparticle-phosphonium ionic liquid composite catalytic systems for deep hydrogenation and hydrodeoxygenation reactions

Stable metal nanoparticles in tetraalkylphosphonium ionic liquids can catalyze hydrogenations, as well as phenol hydrodeoxygenation, owing to presence of adventitious borates.

Energy Efficient Capture and Release of Carbon Dioxide in Tetraalkyl Phosphonium and Tetraalkyl Ammonium Ionic Liquids

Described herein is an electrochemical method for the energy efficient capture and release of CO2 that employs electrochemically-generated thiolates as the CO2 capture agents. In N,N-dimethylformamide at glassy carbon electrodes the onset of CO2 reduction precludes capture by electrochemically generated thiolates. This is not the case in tetraalkyl phosphonium and tetraalkyl ammonium ionic liquids. In these media saturated with CO2, electrochemical reduction of disulfides to thiolates proceeds via a two-electron process with potential inversion.1 One-electron reduction of the disulfide results in dissociative electron transfer (DET), the first step of which is the formation of a short-lived radical anion.2 The S–S σ bond of the radical anion is subsequently cleaved leading to a thiolate and a sulfur-based radical.2 Resultant sulfur radicals are reduced at potentials positive of the potential applied for reduction of the corresponding disulfide. Thus, electrochemical thiolate generation is best formulated as a two-electron reduction with concomitant disulfide cleavage.3 In this presentation we will show that the potent, electrochemically generated sulfur nucleophiles capture CO2 via a facile SN2 reaction leading to formation of a thiocarbonate (Scheme 1). We will further demonstrate that the mechanism for the release of CO2 and regeneration of the disulfide is the one-electron Kolbe oxidation of the thiocarbonate followed by coupling of two sulfur radicals (Scheme 2).4 Cyclic voltammograms show that thiocarbonate oxidation occurs at potentials positive of thiolate oxidation. Increases in the peak-to-peak separation between thiolate oxidation and thiocarbonate oxidation have been ameliorated by targeted modifications to the disulfide. (1) Evans, D. H. Chem. Rev. 2008, 108, 2113–2144.(2) (a) Antonello, S.; Benassi, R.; Gavioli, G.; Taddei, F.; Maran, F. J. Am. Chem. Soc. 2002, 104, 7529–7538. (b) Meneses, A. B.; Antonello, S.; Arévalo, M. C.; Gonzáles, C. C.; Sharma, J.; Wallette, A. N.; Workentin, M. S.; Maran, F. Chem. Eur. J. 2007, 13, 7983–7995.(3) Hall, G. B.; Kottani, R.; Felton, G. A. N.; Yamamoto, T.; Evans, D. H.; Glass, R. S.; Lichtenberger, D. L. J. Am. Chem. Soc. 2014, 136, 4012–4018.(4) Vijh, A. K.; Conway, B. E.; Chem. Rev. 1967, 67, 623–664.

Hg(II) removal from HCl solutions using a tetraalkylphosphonium ionic liquid impregnated onto Amberlite XAD‐7

ABSTRACTExtractant impregnated resins (EIRs) were prepared by impregnation of Amberlite XAD‐7 with tetraalkylphosphonium chloride ionic liquid (IL). The EIRs were tested for the sorption of Hg(II) in HCl solutions. Mercury is bound on the EIR through an ion exchange mechanism involving chloroanionic species and the IL. The effect of HCl concentration and IL content is studied and the sorption isotherms are obtained in 1 M HCl solutions: the sorption capacity linearly increases with IL loading up to 100 mg Hg L−1. A little fraction of the IL immobilized on the resin (about 40 mg IL g−1) is tightly bound to the polymer limiting its reactivity with metal ions. The uptake kinetics are mainly controlled by intraparticle diffusion. At high IL loading the kinetics are slowed down, while the temperature has a limited impact. Nitric acid can be used for desorbing mercury and recycling the EIR for at least five cycles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41086.

Design, synthesis, catalytic application, and strategic redispersion of plasmonic silver nanoparticles in ionic liquid media

Silver nanoparticles synthesized in tetraalkylphosphonium ionic liquids are found to be excellent catalysts for borohydride-induced reductive degeneration of Eosin-Y, a dye that has been classified as a Class 3 carcinogen by the International Agency for Research on Cancer. TEM images indicated that the size of the Ag nanoparticles was significantly influenced by heat-induced sintering. A strategy was devised to redisperse smaller Ag nanoparticles from their aggregated/sintered counterparts via a two-step protocol that involved oxidative etching of Ag nanoparticles, followed by a re-reduction step. This protocol led to a reduction in the sintered Ag nanoparticle size from 15.7±6.1nm to 3.7±0.8nm, which was consistent with the size of the as-synthesized nanoparticles. The as-synthesized and the redispersed Ag nanoparticles were found to catalyze the bleaching of Eosin-Y with comparable efficiencies; first order rate constants for Eosin Y reduction were ∼8 times higher for smaller Ag nanoparticles compared to their sintered counterparts. An examination of the kinetics of Ag nanoparticle etching was performed via temperature-controlled UV–vis spectroscopy. Changes in the oxidation state of Ag during this sequence of events were also followed by in situ X-ray absorption spectroscopy of Ag nanoparticles in the ionic liquid.

Bismuth(III) recovery from hydrochloric acid solutions using Amberlite XAD-7 impregnated with a tetraalkylphosphonium ionic liquid

An Ionic Liquid (IL) (Cyphos IL 101: tetradecyl(trihexyl)phosphonium chloride was immobilized on Amberlite XAD-7 for preparing extractant impregnated resins (EIRs). The IL content was varied between 59 and 586mgILg−1 EIR. The EIRs were tested for Bi(III) recovery from (0.01–8M) HCl solutions. The EIRs were very efficient at extracting Bi(III), the sorption efficiency increased with IL content in the resin, but decreased with HCl concentration. Bi(III) was extracted through an ion exchange mechanism involving the binding of its anionic chloro-complexes to IL phosphonium cation. Sorption isotherms were fitted with the Langmuir equation and they were found to be very favorable with maximum sorption capacities up to 84.3mgBig−1 EIR (in 1M HCl solution using an EIR with 401mgLig−1 EIR at 20°C). Temperature slightly influenced Bi(III) sorption capacity. Bi(III) recovery selectivity was studied in bimetallic (1M HCl) solutions, where, Cu(II) and Ni(II) were not removed but Zn(II) was partially extracted slightly affecting Bi(III) recovery. Sorption kinetics was not affected by agitation speed: the resistance to film diffusion is not the limiting step. The uptake kinetics were controlled by the resistance to intraparticle diffusion. The intraparticle diffusivity coefficients decreased with increasing IL loading but increased with temperature due to the decrease of IL viscosity (in the EIRs). Bi(III) can be easily desorbed from EIRs using either citric acid, nitric acid or sodium sulfate solutions. The EIRs could be recycled maintaining high efficiencies for sorption and desorption for at least five cycles.

Spectroscopic and photophysical study of the demetallation of a zinc porphyrin and the aggregation of its free base in a tetraalkylphosphonium ionic liquid

Dissolving zinc tetraphenylporphyrin in the tetraalkylphosphonium chloride ionic liquid P4448Cl results in progressive demetallation of the solute and quantitative production of the free base porphyrin. Aggregation of the free base occurs in which the monomer and J aggregates are in fully reversible thermal equilibrium in the ionic liquid. The thermodynamic, kinetic and spectroscopic behaviour of this system is described based on absorption, emission and excited state lifetime measurements. Both the thermodynamics of the ground state aggregation and the kinetics of the excited state relaxation processes are unusual due to the particular role played by the ionic liquid solvent.

Hybrid macroporous Pd catalytic discs for 4-nitroaniline hydrogenation: Contribution of the alginate-tetraalkylphosphonium ionic liquid support

Tetraalkylphosphonium ionic liquid (IL) was immobilized in a composite material made of alginate and cellulose fibers (to strengthen the gel) conditioned under the form of highly porous discs. These materials have been used for immobilizing Pd(II) by adsorption from HCl solutions. The metal reduction allows to prepare a catalytic material that was successfully used for the hydrogenation of 4-nitroaniline into p-phenylenediamine using formic acid as the hydrogen donor. The main objective of the study is to understand the contribution of the IL in the catalytic activity. The hydrogenation kinetics were compared for raw material (containing the IL) and for methanol-washed material (without IL) for 8 successive catalytic runs. The presence of the IL allows to stabilize Pd micro/nanoparticles and prevents their release to the solution.

Aerobic oxidation of α,β-unsaturated alcohols using sequentially-grown AuPd nanoparticles in water and tetraalkylphosphonium ionic liquids

Metallic and bimetallic nanoparticles (NPs) (Au, Pd, and AuPd) were synthesized in water with poly(vinylpyrroldine) (PVP) as a polymer stabilizer, as well as in tetraalkylphosphonium chloride ionic liquids (ILs). A borohydride reduction technique was used for the preparation of the monometallic NPs, while a sequential reduction strategy was seen to generate the putative core–shell varieties. Pd and sequentially grown Au–Pd NPs were seen to serve as efficient catalysts for the oxidation of α,β-unsaturated alcohols, while the Au NPs themselves showed minimal activity. However, a system with both Au NPs and a Pd(II) salt (K2PdCl4) also efficiently catalyzed the oxidation reaction in water. A number of aliphatic and aromatic unsaturated alcohols were oxidized using oxygen as an oxidant with these as-prepared catalysts at 60°C in the absence of base. TEM and EXAFS studies of the nanoparticle catalysts before and after the oxidation reaction revealed that the Pd(II) salt was reduced in situ during catalytic conditions, and that there was large changes in particle size and morphology after catalysis, which suggests Ostwald ripening and the presence of a redox mechanism. In the IL system, the ease of Pd reduction led to high activities for many α,β-unsaturated alcohols in the absence of the Au promoter.