Scott T. Griffin

LIQUID/LIQUID EXTRACTION OF METAL IONS IN ROOM TEMPERATURE IONIC LIQUIDS

The search for more environmentally-friendly reaction media has prompted the development of a wide array of alternative systems that will sustain biphasic separations with aqueous solutions without the use of volatile organic compounds (VOCs). We have begun to employ Room Temperature Ionic Liquids (RTIL), specifically 1-alkyl-3-methylimidazolium hexafluorophosphate ([Cnmim][PF6]), as VOC replacements in liquid/liquid separations of metal ions from aqueous solutions. Here we show that the partitioning of metal ions in these novel biphasic systems is consistent with traditional liquid/liquid separations: the metal ion affinity for the hydrophobic phase necessitates the presence of an extractant. In this report we explore the application of wellknown organic (1-(pyridylazo)-2-napthol, PAN, and (1-thiazolylazo)- 2-napthol, TAN) and inorganic (CN−, OCN−, SCN−, and halides) extractants for partitioning a variety of metal cations between [C4mim][PF6] or [C6mim][PF6] and an aqueous phase. PAN and TAN show pH dependent extraction of CD2+, Co+ Ni2+ and Fe3+ where their partitioning to the RTIL increases at least 2 orders of magnitude from pH 1 to 13. The effect of the halides on the partitioning of Hg2+ complexes increases F− < Cl− < Br− < I−. Pseudohalides, especially SCN−, had the greatest effect on enhancing the partitioning of Hg2+to the RTIL, whereas CN− and OCN− provided little benefit for the extraction of any of the metal ions examined.

Metal ion separations in polyethylene glycol-based aqueous biphasic systems : correlation of partitioning behavior with available thermodynamic hydration data

Abstract Solvent extraction, utilizing an oil-water mixture (e.g, chloroform-water) and a suitable complexant, is a proven technology for the selective removal and recovery of metal ions from aqueous solutions. Aqueous biphasic systems (ABS), formed by mixing certain inorganic salts and water-soluble polymers, or by mixing two dissimilar water-soluble polymers, have been studied for more than 40 years for the gentle, non-denaturing separation of fragile biomolecules, yet ABS have been virtually ignored as a possible extraction technology for metal ions. In this report we review our metal ion partitioning work and discuss the three major types of partitioning: (1) those rare instances that the metal ion species present in a given solution partitions to the PEG-rich phase without an extractant; (2) the use of halide salts which produce a metal anion complex that partitions to the PEG-rich phase; and (3) the use of a water-soluble extractant which distributes to the PEG-rich phase. In addition, we correlate the partitioning behavior we observed with available thermodynamic data for metal ions and their complexes.

Ionic liquids with dual biological function: sweet and anti-microbial, hydrophobic quaternary ammonium-based salts

The dual nature of ionic liquids has been exploited to synthesize materials that contain two independent biological functions by combining anti-bacterial quaternary ammonium compounds with artificial sweetener anions. The synthesis and physical properties of eight new ionic liquids, didecyldimethylammonium saccharinate ([DDA][Sac]), didecyldimethylammonium acesulfamate ([DDA][Ace]), benzalkonium saccharinate ([BA][Sac]), benzalkonium acesulfamate ([BA][Ace]), hexadecylpyridinium saccharinate ([HEX][Sac]), hexadecylpyridinium acesulfamate ([HEX][Ace]), 3-hydroxy-1-octyloxymethylpyridinium saccharinate ([1-(OctOMe)-3-OH-Py][Sac]), and 3-hydroxy-1-octyloxymethylpyridinium acesulfamate ([1-(OctOMe)-3-OH-Py][Ace]), are reported, as well as the single crystal structures for [HEX][Ace] and [1-(OctOMe)-3-OH-Py][Sac]. Determination of anti-microbial activities is described for six of the ILs. While some exhibited decreased anti-microbial activity others showed a dramatic increase. For two of the ionic liquids, [DDA][Sac] and [DDA][ACE], oral toxicity, skin irritation, and deterrent activity was also established. Unfortunately, both ILs received a Category 4 (harmful) rating for oral toxicity and skin irritation. However, deterrent activity experiments point to use as an insect deterrent, as both ILs scored either “very good” or “good” against several types of insects.

Long alkyl chain quaternary ammonium-based ionic liquids and potential applications

Due to the high interest in the applications of ionic liquids, new, cheaper, multifunctional ionic liquids which are easy to prepare are highly desired. Here, we present a new group of air- and moisture-stable, hydrophobic ammonium-based ionic liquids and their properties, including the single-crystal X-ray structure of benzethonium nitrate. These salts have utility as anti-bacterial, anti-fungal agents. Additionally, the potential application of these ionic liquids for wood preservation was tested with positive results. The toxicity of benzalkonium and didecyldimethylammonium nitrates were studied and are presented herein.

Ionic liquids via reaction of the zwitterionic 1,3-dimethylimidazolium-2-carboxylate with protic acids. Overcoming synthetic limitations and establishing new halide free protocols for the formation of ILs

The previously reported preparation of 1,3-dimethylimidazolium salts by the reaction of 1,3-dialkylimidazolium-2-carboxylate zwitterions with protic acids has been reinvestigated in detail, leading to the identification of two competing reactions: isomerisation and decarboxylation. The ability to control both pathways allows this methodology to be used as an effective, green, waste-free approach to readily prepare a wide range of ionic liquids in high yields. Additionally, this reaction protocol opens new possibilities in the formation of other imidazolium salts, whose syntheses were previously either very expensive (due to ion exchange protocols involving metals like Ag) or difficult to achieve (due to multiple extractions and large quantities of hard to remove inorganic by-products).

Partitioning of small organic molecules in aqueous biphasic systems

Aqueous biphasic systems (ABS) are suitable for the separation of small organic molecules in industrial and environmental applications and thus, it is important to correlate partitioning behavior of model organic solutes with their structure in order to develop predictive models. The partitioning behavior of five, uncharged, substituted benzenes (benzene, toluene. chlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene) were studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts (K3PO4, K2CO3, (NH4)2SO4 and NaOH). For a given solute and a defined concentration of salt, the partition coefficients increase as the deltaGhyd value of the salt anion becomes more negative (e.g., Dbenzene increases in the order OH- <SO42- <CO32- <PO43-). In a given salt, the distribution ratios increase in the order benzene<toluene<chlorobenzene< 1,4-dichlorobenzene< 1,2,4-trichlorobenzene. The partitioning behavior of the solutes in PEG-salt ABS was found to be strongly correlated with their partitioning coefficients in 1-octanol-water biphasic systems.

Synthesis and X-ray structure determination of highly active Pd(II), Pd(I), and Pd(0) complexes of di(tert-butyl)neopentylphosphine (DTBNpP) in the arylation of amines and ketones.

The air-stable complex Pd(η(3)-allyl)(DTBNpP)Cl (DTBNpP = di(tert-butyl)neopentylphosphine) serves as a highly efficient precatalyst for the arylation of amines and enolates using aryl bromides and chlorides under mild conditions with yields ranging from 74% to 98%. Amination reactions of aryl bromides were carried out using 1-2 mol % Pd(η(3)-allyl)(DTBNpP)Cl at 23-50 °C without the need to exclude oxygen or moisture. The C-N coupling of the aryl chlorides occurred at relatively lower temperature (80-100 °C) and catalyst loading (1 mol %) using the Pd(η(3)-allyl)(DTBNpP)Cl precatalyst than the catalyst generated in situ from DTBNpP and Pd(2)(dba)(3) (100-140 °C, 2-5 mol % Pd). Other Pd(DTBNpP)(2)-based complexes, (Pd(DTBNpP)(2) and Pd(DTBNpP)(2)Cl(2)) were ineffective precatalysts under identical conditions for the amination reactions. Both Pd(DTBNpP)(2) and Pd(DTBNpP)(2)Cl(2) precatalysts gave nearly quantitative conversions to the product in the α-arylation of propiophenone with p-chlorotoluene and p-bromoanisole at a substrate/catalyst loading of 100/1. At lower substrate/catalyst loading (1000/1), the conversions were lower but comparable to that of Pd(t-Bu(3)P)(2). In many cases, the tri-tert-butylphosphine (TTBP) based Pd(I) dimer, [Pd(μ-Br)(TTBP)](2), stood out to be the most reactive catalyst under identical conditions for the enolate arylation. Interestingly, the air-stable Pd(I) dimer, Pd(2)(DTBNpP)(2)(μ-Cl)(μ-allyl), was less active in comparison to [Pd(μ-Br)(TTBP)](2) and Pd(η(3)-allyl)(DTBNpP)Cl. The X-ray crystal structures of Pd(η(3)-allyl)(DTBNpP)Cl, Pd(DTBNpP)(2)Cl(2), Pd(DTBNpP)(2), and Pd(2)(DTBNpP)(2)(μ-Cl)(μ-allyl) are reported in this paper along with initial studies on the catalyst activation of the Pd(η(3)-allyl)(DTBNpP)Cl precatalyst.

Synthesis and properties of chiral imidazolium ionic liquids with a (1R, 2S, 5R)-(-)-menthoxymethyl substituent

A series of 1-[(1R,2S,5R)-(−)-menthoxymethyl]-3-alkylimidazolium salts have been synthesized, producing both hydrophilic and hydrophobic chiral imidazolium ionic liquids. Their physicochemical properties, single-crystal X-ray structures, antimicrobial activities, and antielectrostatic effects were determined and these compounds have proven to represent not only potential new solvents in asymmetric synthesis, but also effective, disinfectants with antielectrostatic activity. Given the number and diversities of the possible conformations and interionic interactions, coupled with the chiral nature of the cations, it should come as no surprise that these salts exhibit ionic liquid behavior and are so difficult to crystallize.

Flexible coordination environments of lanthanide complexes grown from chloride-based ionic liquids

Hydrated lanthanide(III) chlorides, LnCl3·xH2O (Ln = La, Pr, Nd, Sm, Eu, Gd; x = 6–7) readily dissolve in the low melting ionic liquid 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl) in an open vessel at 110 °C, and upon cooling crystallize as the anhydrous [C2mim]3[LnCl6]. The crystal structures exhibit a face-centered packing arrangement of the [LnCl6]3− anions, with the cations located as slip aligned pairs in the void spaces which participate in hydrogen-bonding to chlorides. A second crystalline form of the Gd3+ complex, GdCl3(OH2)4·2([C2mim]Cl), was isolated when the above reaction was conducted in a sealed system. For comparison, a third Gd3+ compound was grown from the ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) using the same unsealed conditions as above, and was found to be [C4mim]3[GdCl6]. This compound exhibits a different packing arrangement to that observed for the [C2mim]+ analogs. Based on these findings, ILs would appear to offer new crystallization process options based on their often high thermal stabilities and low to negligible vapor pressures.

PARTITIONING OF AROMATIC MOLECULES IN AQUEOUS BIPHASIC SYSTEMS

ABSTRACT Aqueous biphasic systems (ABS) may be suitable for the separation of aromatic molecules in industrial and environmental settings; hence it is invaluable to have predictive models of partitioning behavior in these systems for design and evaluation purposes. In a continuing study of the partition of small aromatic organic molecules, the distribution of several relatively hydrophilic substituted benzene species is reported. The partitioning behavior of five charged substituted benzene species (phthalic acid, 4-hydroxybenzoic acid, benzoic acid, salicylic acid, and p-toluic acid) and one uncharged species (1,3-dinitrobenzene) has been studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts [K3PO4, K2CO3, (NH4)2SO4, and NaOH]. Comparison has been made with published data on the partitioning of these solutes in 1-octanol/water biphasic systems. In general, the partition of these species may be understood in terms of the free energ...