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Kenneth R Seddon

Publications and source records attributed to Kenneth R Seddon.

16 recordsLinked to original sources
PubMed2007

Decolorization of ionic liquids for spectroscopy.

It has been widely recognized that although ionic liquids should be colorless, they are frequently not. Colored samples appear to be pure by most analytical techniques (e.g., NMR spectroscopy, mass spectrometry, HPLC, and ion chromatography), and there have been many attempts to identify the source of color in our own laboratories and others-after 20 years the best that can be said is that the impurities are at a very low level (probably parts per billion) with very high molar extinction coefficients. In this paper, we do not identify these impurities but describe a practical method for removing them for spectrochemical applications. We clearly note that the method is not "green", but we anticipate that it will only be applied to the small volumes of ionic liquids required for fundamental spectroscopic studies in academia but not in industrial processes.

Journal Article↗
PubMed2006

Mutually immiscible ionic liquids.

This work presents the novel discovery of room-temperature ionic liquids that are mutually immiscible, some of which are also immiscible with solvents as diverse as water and alkanes; an archetypal biphasic system is trihexyltetradecylphosphonium chloride with 1-alkyl-3-methylimidazolium chloride (where the alkyl group is shorter than hexyl).

Journal Article↗
PubMed2006

Uranium halide complexes in ionic liquids: an electrochemical and structural study.

The electrochemistry of the salts, [emim]2[UBr6] and [emim]2[UO2Br4] ([emim] = 1-ethyl-3-methylimidazolium), has been investigated in both a basic and an acidic bromoaluminate(III) ionic liquid. In the basic ionic liquid, the hexabromo salt undergoes a one-electron reversible reduction process at a stationary glassy carbon disc electrode, while the tetrabromodioxo salt was reduced to a uranium(IV) species by an irreversible two-electron process with the simultaneous transfer of oxide to the ionic liquid. On the other hand, dissolution of either of the salts in an acidic bromoaluminate(III) ionic liquid resulted in the formation of the same electroactive species. The solid state structures of the uranium chloride salts, [emim]2[UCl6] and [emim]2[UO2Cl4], have previously been reported, but have now been re-evaluated using a new statistical model developed in our group, to determine the presence or absence of weak hydrogen bonding interactions in the crystalline state.

Journal Article↗
PubMed2006

The distillation and volatility of ionic liquids.

It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200-300 degrees C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.

Journal Article↗
PubMed2005

Predicting physical properties of ionic liquids.

A simple method to predict the densities of a range of ionic liquids from their surface tensions, and vice versa, using a surface-tension-weighted molar volume, the parachor, is reported. The parachors of ionic liquids containing 1-alkyl-3-methylimidazolium cations were determined experimentally, but were also calculated directly from their structural compositions using existing parachor contribution data for neutral compounds. The calculated and experimentally determined parachors were remarkably similar, and the latter data were subsequently employed to predict the densities and surface tensions of the investigated ionic liquids. Using a similar approach, the molar refractions of ionic liquids were determined experimentally, as well as calculated using existing molar refraction contribution data for uncharged compounds. The calculated molar refraction data were employed to predict the refractive indices of the ionic liquids from their surface tensions. The errors involved in the refractive index predictions were much higher than the analogous predictions employing the parachor, but nevertheless demonstrated the potential for developing parachor and molar refraction contribution data for ions as tools to predict ionic liquid physical properties.

Chemical Phenomena↗
PubMed2005

Raman and ab initio studies of simple and binary 1-alkyl-3-methylimidazolium ionic liquids.

Raman spectra of the ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]), 1-hexyl-3-methylimidazolium chloride ([C6mim]Cl), and 1-hexyl-3-methylimidazolium hexafluorophosphate ([C6mim][PF6]), and binary mixtures thereof, have been assigned using ab initio MP2 calculations. The previously reported anti and gauche forms of the [C4mim]+ cation have been observed, and this study reveals this to be a general feature of the long-chain 1-alkyl derivatives. Analysis of mixtures of [C6mim]Cl and [C6mim][PF6] has provided information on the nature of the hydrogen bonding between the imidazolium headgroup and the anions, and the invariance of the essentially 50:50 mixture of the predominant conformers informs on the nature of glass formation in these systems.

Journal Article↗
PubMed2005

Evidence for lower critical solution behavior in ionic liquid solutions.

Lower critical solution temperatures (LCST)-type of phase diagrams, including the presence of closed loops, have been encountered for the first time in binary and quasi-binary liquid solutions of ionic liquids. Furthermore, the results constitute the first experimental support for the existence of a theoretically postulated, but never encountered, special kind of type VII phase diagram. Two distinct mechanisms are involved in the appearance of demixing upon temperature increase. These findings underlie the presence of specific, oriented interactions between the ionic liquid, 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide, [Cnmim][NTf2], and trichloromethane, as well as aggregation phenomena.

Journal Article↗
PubMed2005

Nanoclusters in ionic liquids: evidence for N-heterocyclic carbene formation from imidazolium-based ionic liquids detected by (2)H NMR.

The mystery of how 1,3-substituted imidazolium-based ionic liquids (ILs) can provide high stabilization for transition-metal(0) nanoclusters, that is, in the absence of the usual strongly coordinating anions, has been probed. 2H NMR product and kinetic studies of 1,3-substituted imidazolium ILs under D2 reveal that nanocluster-catalyzed H/D exchange occurs at the 2- (as well as at the 4-, 5-, and 8-) C-H positions of the imidazolium cation. The results (i) provide compelling evidence that N-heterocyclic carbene formation and ligation of nanoclusters is occurring in ILs; and (ii) argue that N-heterocyclic carbenes merit further investigation as heretofore unappreciated stabilizers of transition-metal nanoclusters.

Journal Article↗
PubMed2005

Deviations from ideality in mixtures of two ionic liquids containing a common ion.

Excess molar volumes of six binary mixtures composed of two ionic liquids of the 1-methyl-3-alkyl-imidazolium bis(trifluoromethylsulfonyl)amide family -- ([C(m)()mim] + [C(n)()mim])[NTf(2)] with n and m ranging from 2 to 10 -- were measured for several compositions at 298 and 333 K. Similarly, three other binary systems containing [C(4)mim](+) (1-methyl-3-butylimidazolium) as a common cation have been studied: [C(4)mim]([NTf(2)] + [PF(6)]), [C(4)mim]([NTf(2)] + [BF(4)]) and [C(4)mim]([BF(4)] + [PF(6)]). Thus, the mixing process of two distinct ions of equal sign embedded in a constant field network of a given counterion was analyzed. All systems exhibit small, positive V(E) values of the order of a few tenths of cm(3) mol(-1), which are essentially temperature and pressure independent. The results show additive trends, for instance, the V(E) values become larger as the difference between the alkyl chain lengths of the two cations increases. The Flory theory of mixtures provides a useful, semiquantitative correlation between the excess volumes and excess enthalpies in these systems, allowing for comparison with analogous results obtained within the linear primary alcohols.

Journal Article↗
PubMed2004

A structural and electrochemical investigation of 1-alkyl-3-methylimidazolium salts of the nitratodioxouranate(VI) anions [[UO2(NO3)2]2(mu 4-C2O4)]2-, [UO2(NO3)3]-, and [UO2(NO3)4]2-.

The properties of the 1-butyl-3-methylimidazolium salt of the dinuclear mu(4)-(O,O,O',O'-ethane-1,2-dioato)bis[bis(nitrato-O,O)dioxouranate(VI)] anion have been investigated using electrochemistry, single-crystal X-ray crystallography, and extended X-ray absorbance fine structure spectroscopy: the anion structures from these last two techniques are in excellent agreement with each other. Electrochemical reduction of the complex leads to the a two-electron metal-centered reduction of U(VI) to U(IV), and the production of UO(2), or a complex containing UO(2). Under normal conditions, this leads to the coating of the electrode with a passivating film. The presence of volatile organic compounds in the ionic liquids 1-alkyl-3-methylimidazolium nitrate (where the 1-alkyl chain was methyl, ethyl, propyl, butyl, pentyl, hexyl, dodecyl, hexadecyl, or octadecyl) during the oxidative dissolution of uranium(IV) oxide led to the formation of a yellow precipitate. To understand the effect of the cation upon the composition and structure of the precipitates, 1-alkyl-3-methylimidazolium salts of a number of nitratodioxouranate(VI) complexes were synthesized and then analyzed using X-ray crystallography. It was demonstrated that the length of the 1-alkyl chain played an important role, not only in the composition of the complex salt, but also in the synthesis of dinuclear anions containing the bridging mu(4)-(O,O,O',O'-ethane-1,2-dioato), or oxalato, ligand, by protecting it from further oxidation.

Journal Article↗
PubMed2004

Paradigm confirmed: the first use of ionic liquids to dramatically influence the outcome of chemical reactions.

It has been an unproven paradigm that the choice of which ionic liquid to use in a chemical reaction can have a dramatic effect on the outcome of that chemical reaction. We demonstrate, for the first time, that the reaction of toluene and nitric acid in three different ionic liquids gives rise to three completely different products in high yield. Furthermore, ionic liquids can catalyze these reactions with the only byproduct being water. [reaction: see text]

Journal Article↗
PubMed2002

Precipitation of a dioxouranium(VI) species from a room temperature ionic liquid medium.

The novel complex 1-butyl-3-methylimidazolium mu(4)-(O,O,O',O'-ethane-1,2-dioato)-bis[bis(nitrato-O,O)dioxouranate(VI)] (1) has been precipitated from a room-temperature ionic liquid medium containing 1-butyl-3-methylimidazolium nitrate, nitric acid, and acetone. X-ray analysis of complex 1 shows the unit cell contains four [C(4)mim](+) cations and two independent [[UO(2))(NO(3))(2)](2)(mu(4)-C(2)O(4))](2-) moieties, both of which are located about inversion centers. The [C(4)mim](+) cations are arranged such that they produce large channels in which the anions are located. This arrangement of [[(UO(2))(NO(3))(2)](2)(mu(4)-C(2)O(4))](2-) groups is unique to this compound. Crystal data for compound 1: M = 1154.56, monoclinic, space group P2(1)/c, a = 15.452(2) A, b = 20.354(3) A, c = 10.822(4) A, beta = 106.84(2) degrees, U = 3258(1) A(-)(3), Z = 4, mu = 10.023 mm(-1), R(int) = 0.0788.

Journal Article↗