William R. Pitner

Selective extraction of emerging contaminants from water samples by dispersive liquid–liquid microextraction using functionalized ionic liquids

Functionalized ionic liquids containing the tris(pentafluoroethyl)trifluorophosphate (FAP) anion were used as extraction solvents in dispersive liquid-liquid microextraction (DLLME) for the extraction of 14 emerging contaminants from water samples. The extraction efficiencies and selectivities were compared to those of an in situ IL DLLME method which uses an in situ metathesis reaction to exchange 1-butyl-3-methylimidazolium chloride (BMIM-Cl) to 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (BMIM-NTf(2)). Compounds containing tertiary amine functionality were extracted with high selectivity and sensitivity by the 1-(6-amino-hexyl)-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (HNH(2)MPL-FAP) IL compared to other FAP-based ILs and the BMIM-NTf(2) IL. On the other hand, polar or acidic compounds without amine groups exhibited higher enrichment factors using the BMIM-NTf(2) IL. The detection limits for the studied analytes varied from 0.1 to 55.1 μg/L using the traditional IL DLLME method with the HNH(2)MPL-FAP IL as extraction solvent, and from 0.1 to 55.8 μg/L using in situ IL DLLME method with BMIM-Cl+LiNTf(2) as extraction solvent. A 93-fold decrease in the detection limit of caffeine was observed when using the HNH(2)MPL-FAP IL compared to that obtained using in situ IL DLLME method. Real water samples including tap water and creek water were analyzed with both IL DLLME methods and yielded recoveries ranging from 91% to 110%.

Using the solvation parameter model to characterize functionalized ionic liquids containing the tris (pentafluoroethyl)trifluorophosphate (FAP) anion

AbstractIonic liquids (ILs) containing the tris(pentafluoroethyl)trifluorophosphate anion [FAP]− have attracted increased attention due to their unique properties including ultrahigh hydrophobicity, hydrolytic stability, and wide electrochemical window. In this study, the solvation parameter model is used via gas chromatography to characterize the solvation interactions of seven ILs containing amino, ester, and hydroxyl functional groups appended to the cation and paired with [FAP]−, as well as three ILs containing the bis[(trifluoromethyl)sulfonyl]imide anion [NTf2]−. The role of the functional groups, nature of the counter anion, and cation type on the system constants were evaluated. ILs containing [FAP]− possessed lower hydrogen bond basicity than NTf2-based ILs having the same cationic component; in the case of hydroxyl-functionalized cations, the presence of [FAP]− led to an enhancement of the hydrogen bond acidity, relative to the NTf2-analogs. The system constants support the argument that [FAP]− weakly coordinates the cation and any appended functional groups, promoting properties of the cation which might be masked by stronger interactions with other anion systems. The chromatographic performance of the IL stationary phases was evaluated by examining the retention behavior and separation selectivity for chosen analytes. The results from this work can be used as a guide for choosing FAP-based ILs capable of exhibiting desired solvation properties while retaining important physical properties including high thermal stability and high hydrophobicity. FigureIn this study, the solvation parameter model is used via gas chromatography to characterize the solvation interactions of seven ILs containing amino, ester, and hydroxyl functional groups appended to the cation and paired with tris(pentafluoroethyl)trifluorophosphate [FAP]−, as well as three ILs containing the bis[(trifluoromethyl)sulfonyl]imide anion [NTf2]−.

Evaluating the solvation properties of functionalized ionic liquids with varied cation/anion composition using the solvation parameter model

Ionic liquids (ILs) are promising gas chromatography (GC) stationary phases due to their high thermal stability, negligible vapor pressure, and ability to solvate a broad range of analytes. The tunability of ILs allows for structure modification in pursuit of enhanced separation selectivity and control of analyte elution order. In this study, the solvation parameter model is used to characterize the solvation interactions of fifteen ILs containing various cationic functional groups (i.e., dimethylamino, hydroxyl, and ether) and cation types paired with various counter anions, namely, tris(pentafluoroethyl)trifluorophosphate (FAP(-)), bis[(trifluoromethyl)sulfonyl]imide (NTf(2)(-)), thiocyanate (SCN(-)), tricyanomethide (C(CN)(3)(-)), tetracyanoborate (B(CN)(4)(-)), and bis[oxalate(2-)]borate (BOB(-)). The presence of functional groups affected the hydrogen bond basicity, hydrogen bond acidity, as well as dispersion interactions of the resulting ILs, while the change of cation type yielded modest influence on the dipolarity. The switch of counter anions in unfunctionalized ILs produced compounds with higher dipolarity and hydrogen bond basicity. The dipolarity and hydrogen bond basicity of ILs possessing cyano-containing anions appeared to be inversely proportional to the cyano content of the anion. The modification of IL structure resulted in a significant effect on the retention behavior as well as separation selectivity for many solutes, including reversed elution orders of some analytes. This study provides one of the most comprehensive examinations up-to-date on the relation between IL structure and the resulting solvation characteristics and gives tremendous insight into choosing suitable ILs as GC stationary phases for solute specific separations.

Overcoming hydrolytic sensitivity and low solubility of phosphitylation reagents by combining ionic liquids with mechanochemistry

Ionic liquids have been used in combination with ball milling on a range of chlorophosphoramidite reagents to phosphitylate nucleosides and 2-deoxynucleosides. The enhanced stability offered by the ionic liquid mediated processes combined with efficient mass transfer induced by ball milling has enabled excellent yields to be obtained even when using small dialkyl amino groups as well as the more commonly used diisopropylamino protection.

Task-specific ionic liquids as reaction media for the cobalt-catalysed cyclotrimerisation reaction of arylethynes

The use of nitrile-functionalised ionic liquids as solvents for cobalt-catalysed cyclotrimerisation reactions of monosubstituted aromatic alkynes is reported; the nitrile functionality stabilises the transient cobalt(I) catalytic species and ensures good conversions.

Selective synthesis of chlorophosphoramidites using ionic liquids

A range of chlorophosphoramidites have been prepared in ionic liquids and compared with material synthesised in molecular solvents. Through the use of ionic liquids as reaction media the moisture sensitivity and impurity issues hampering existing traditional synthetic routes have been eased. Not only can stock chemicals be used without purification, but the reactions may be conducted at room temperature and at high concentrations. Furthermore, reaction times are reduced and rapid addition of reagents is possible whilst retaining tight control over product selectivity. Beyond their role as reaction media, ionic liquids also present a unique storage medium for these highly moisture sensitive chlorophosphoramidites.

Controlled chemistry of Moisture Sensitive Reagents in Ionic Liquids

PCl3 and POCl3 are key synthetic precursors in a wide range of chemical processes, required in the synthesis of compounds ranging from bulk chemicals such as pesticides, flame retardants and plasticizers to the advanced synthetic intermediates and reagents, therapeutic precursors and metal catalysts ligands. However, whether neat or in organic solvents, these reagents and their derivatives are highly air and water sensitive and must be used under strictly anhydrous conditions, often in excess at low temperatures to allow for some level of control in order to achieve chemoselectivity and avoid side-product formation. For instance, excess of phosphitylating reagent must be used in aprotic organic solvents at low temperature under anhydrous and dissolution conditions in order to obtain mono-derivatised chlorophosphines and overcome the high chemical reactivity of the trivalent chlorophosphine’s P-Cl bonds. As such, by virtue of their chemical instability in organic media, the use of chlorophosphines in the direct phosphitylation of alcohols and amines has been limited and very difficult to control. In industry, the reagents used and available for phosphitylation reactions have been restricted to compounds such as dibenzyloxychlorophosphine, dichlorodiisopropylaminophosphite, chlorocyanoethyldiisopropyl-aminophosphite and cyanoethyl-bisdiisopropylaminophosphite. Although these reagents are commercially available and used extensively as precursors in the synthesis of many phosphoruscontaining fine chemicals, major variability can be observed in their purity and stability upon storage. As a consequence, yields of phosphitylation reactions are highly variable and thus compromise overall synthetic efficiency in particular that of automated processes such as solid phase synthesis of oligonucleotides, which require highly pure nucleoside phosphoramidites to be effective. We have established that ionic liquids can alleviate many of the issues surrounding the use and preparation of P-X containing compounds as synthetic reagents. Initially, the stability of PCl3/POCl3 in ILs and the controllable reactivity of PCl3 in this medium has been demonstrated. In addition, in the area of PCl3 manipulation, ILs was shown to permit the selective conversion of individual P-Cl bonds (Figure 1) to be performed with control not observed in molecular solvent systems. This has been particularly valuable in the formation of nucleotide phosphoramidites.