Highly selective electrochemical fluorination of organic compounds in ionic liquids

Recent studies on electrochemical partial fluorination in ionic liquid fluoride salts are reviewed. At first, historical background and some problems of electrochemical fluorination in organic solvents are briefly mentioned. Solvent-free electrochemical fluorinations in ionic liquids are explained as follows. Ultrasonication was found to improve both the yield and current efficiency for electrochemical fluorination of α-phenylthioacetate, which is mainly attributable to marked mass transport promotion of the substrate and the suppression of anode passivation. Highly regioselective and efficient fluorination of cyclic ethers, lactones, and cyclic carbonate was achieved in Et₄NF·4HF and Et₃N·5HF. Selective fluorination of hardly oxidizable phthalide was realized using a combination of imidazolium and fluoride ionic liquids. The unique effect of imidazolium ionic liquids on electrochemical fluorodesulfurization of 3-phenylthiophthalide was explained. Reuse of ionic liquids for electrochemical fluorination is also possible.     

Effects of additives on anodic fluorination in ionic liquid hydrogen fluoride salts

Anodic fluorination of ethyl α-(2-pyrimidylthio)acetate in neat ionic liquid hydrogen fluoride salts (Et₃N–3HF, Et₄NF–4HF, Et₄NF–5HF) was investigated to avoid an anode passivation, which sometimes occurs during anodic fluorination in organic solvent. In order to improve the yield of fluorinated product, polyether having coordination ability to cation and anodic stability was introduced to the reaction system as additives (3%). Furthermore, such additives were found to be also effective for anodic fluorodesulfurization of 4-phenylthio-1,3-dioxolan-2-one in neat ionic liquid system.     

Electrolytic partial fluorination of organic compounds. Part 78: Regioselective anodic fluorination of 2-oxazolidinones

Various 2-oxazolidinones were galvanostatically electrooxidized in the presence of various fluoride salts. It was found that a fluorine atom was introduced to the α-position of the nitrogen atom of N-acyl- and N-alkoxycarbonyl-2-oxazolidinones to provide the corresponding α-fluorinated products in moderate to good yields. In the case of N-phenoxycarbonyl derivative, fluorination took place on the phenyl group selectively.     

Unique solvent effect on photochemistry of ortho-alkylphenacyl benzoates

Photolysis of 2,4,6-trialkylphenacyl benzoates gives not only the corresponding indanones and benzoic acid, but also the corresponding benzocyclobutenols (CBs), which are also detected in the photolysis of mono-alkylphenacyl benzoates for the first time. The product selectivity was heavily dependent upon solvents and o-alkyl group. H-bonding acceptor solvents strongly favor the formation of the CB. As the size of the o-alkyl group increases, the relative amount of the CB increases.     

Ionic liquid based three-phase liquid-liquid-liquid solvent bar microextraction for the determination of phenols in seawater samples

For the first time, an ionic liquid based three-phase liquid-liquid-liquid solvent bar microextraction (IL-LLL-SBME) was developed for the analysis of phenols in seawater samples. The ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF(6)]), was used as the intermediary solvent for LLL-SBME, enhancing the extraction efficiency for polar analytes. In the procedure, the analytes were extracted from the aqueous sample into the ionic liquid intermediary and finally, back-extracted into an aqueous acceptor solution in the lumen of the hollow fiber. The porous polypropylene membrane acted as a filter to prevent potential interfering materials from being extracted, and no additional cleanup was required. After extraction, the acceptor solution could be directly injected into a high-performance liquid chromatographic system for analysis. Six phenols, 2-nitrophenol, 4-chlorophenol, 2,3-dichlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol were selected here as model compounds for developing and evaluating the method. The most influential extraction parameters were evaluated, including the ionic liquid, the composition of donor solution and acceptor solution, the extraction time and the extraction temperature, the effect of ionic strength, and the agitation speed. Under the most favorable extraction parameters, the method showed good linearity (from 0.05-50 to 0.5-50 μg/L, depending on the analytes) and repeatability of extractions (RSD below 8.3%, n=5). The proposed method was compared to conventional three-phase LLL-SBME and ionic liquid supported hollow fiber protected three-phase liquid-liquid-liquid microextraction, and showed higher extraction efficiency. The proposed method was demonstrated to be a simple, fast, and efficient method for the analysis of phenols from environmental water samples.     

Effective reductive amination of carbonyl compounds with hydrogen catalyzed by iridium complex in organic solvent and in ionic liquid

The direct reductive amination (DRA) of carbonyl compounds with amines has been achieved using homogenous iridium catalyst and gaseous hydrogen. It appeared that the cationic iridium catalyst, [Ir(cod)₂]BF₄, without any other ligands was sufficient for the reaction. For the DRA of the ketone substrates, an ionic liquid, [Bmim]BF₄, was found to be superior to the other organic solvent used. Especially, the counter anion of the ionic liquid has a significant influence on the selectivity, and at the same time, a high reaction temperature was found to be crucial for the excellent selectivity.     

Role of the organic solvent modifier in the reversed phase high-performance liquid chromatography of polypeptides

Summary The retention behaviour of several polypeptide hormones on Bondapak C₁₈ columns has been examined using mobile phases of different acetonitrile percentage compositions containing 15 mM triethylammonium phosphate or 15 mM orthophosphoric acid buffers. Under these elution conditions, the capacity factors and the selectivity parameters of these polypeptide hormones show pronounced dependencies on the volume fraction of the organic solvent modifier. In the range 0–40% acetonitrile, the capacity factors were monotonously attenuated with increasing modifier percentages with the elution order essentially in accord with that hat anticipated for a reversed phase separation mode. At higher concentrations of acetonitrile, retention of the polypeptides to the octadecylsilica support progressively increased with elution order reversals indicative of a normal- or polarphase separation mode. These observations are discussed in terms of the interplay of hydrophobic and silanophilic interactions which occur between the ionised polypeptides and the stationary phase under these changing mobile phase conditions.High Performance Liquid Chromatography of Amino Acids, Peptides and Proteins, XXXII. For previous publication see ref. [1].     

FT-IR study on solvent effects in building blocks of bioactive compounds. V

3-Hydroxy-4-hydroxymethyl pyrrolidin-2-ones, easily prepared from the Baylis–Hillman adduct 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate, are useful intermediates in the synthesis of bioactive compounds. In order to understand the mechanism involved in this reaction, vibrational and Montecarlo molecular mechanics conformational analysis on 1-ethyl-4-methyl-2-hydroxy-3-methylenebutanedioate were carried out, confirming the existence of a low energy intramolecular H-bonded five-member ring.     

Facile nucleophilic fluorination of primary alkyl halides using tetrabutylammonium fluoride in a tert-alcohol medium

Nonpolar protic reaction media such as t-amyl alcohol allow the aliphatic, nucleophilic fluorination reaction of primary haloalkane systems to fluoroalkanes, using tetrabutylammonium fluoride (TBAF), to proceed chemo-selectively at a reasonable reaction rate under mild conditions to afford the fluoro-product in high yield. As an example, the nucleophilic fluorination of 2-(3-iodopropoxy)naphthalene (1a) as the primary haloalkane model compound, with TBAF in acetonitrile as a polar aprotic solvent, CsF in t-amyl alcohol as a nonpolar protic solvent, and TBAF in t-amyl alcohol for 1 h provided 2-(3-fluoropropoxy)naphthalene (2a) in 38, 5, and 76% yields, respectively.     

Some remarks on the SCRF theory of solvent effects and the calculation of proton potentials

Some aspects concerning the self-consistent reaction field theory of solvent effects are discussed. In particular, the variational solution to the non-linear Schrödinger equation is considered; a necessary and sufficient constraint to be added to the standard variational procedure is discussed. The exact solution of the non-linear equation is presented within the molecular orbital approach; correlation defaults to the Hartree-Fock like solutions are stated. Some thermodynamical correspondences are established with the magnitudes calculated with the self-consistent reaction field theory. Finally, we have commented upon the proton potentials calculated within this theory. An INDO calculation of a water trimer has been used as an example to discuss different types of proton translocation potentials.     

Electrolytic partial fluorination of organic compounds. 42.(1) marked solvent effects on regioselective anodic monofluorination of 4-oxo-2-pyrimidyl sulfides

Regioselective anodic monofluorination of 4-oxo-2-pyrimidyl sulfides was investigated under various electrolytic conditions. Anodic fluorination was successfully carried out using Et(4)NF.4HF in dimethoxyethane (DME) to provide the corresponding alpha-fluorinated products in good yields. In contrast, acetonitrile (MeCN) was not suitable for the anodic fluorination due to the severe anode passivation during the electrolysis. A mixed solvent of DME and MeCN was found to be also effective for the fluorination, and the product yield increased with an increase of the ratio of DME to MeCN. The superiority of DME can be explained mainly in terms of the suppression of the anode passivation and enhancement of the nucleophilicity of the fluoride ions. Such marked solvent effects on the anodic fluorination were discussed in detail.     

Synthesis and solvent effects on the electronic absorption and fluorescence spectral properties of substituted zinc phthalocyanines

The synthesis and spectroscopic properties of the following tetra- and octa-substituted aryloxy zinc(II) phthalocyanines are reported for the first time: 1,(4)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (7); 2,(3)-(tetrabenzyloxyphenoxyphthalocyaninato) zinc(II) (8); 2,3-(octabenzyloxyphenoxyphthalocyaninato) zinc(II) (9). The new compounds have been characterized by elemental analysis, IR, ¹H NMR spectroscopy and electronic spectroscopy. Spectroscopic properties of these compounds were investigated in different solvents. Protonation of non-peripherally substituted complex 7 resulted in the splitting and red-shifting of the Q-band. The peripherally substituted derivatives 8 and 9, did not show the split in the Q-band. Fluorescence spectra of the derivatives show Stokes shifts typical of MPc complexes.     

Electrochemical oxidation of substituted benzylamines in aquo-acetic acid medium: substituent and solvent effects

Electrochemical oxidation of nine para- and meta-substituted benzylamines in varying mole fractions of acetic acid in water has been investigated in the presence of 0.1 M sulphuric acid as supporting electrolyte. The oxidation potentials correlate well with Hammett’s substituent constants affording negative reaction constants. The correlation of potential values with macroscopic solvent parameters is non-linear suggesting that the operation of both specific and non-specific solvent-solvent-solute interaction mechanisms. Multiple correlation analysis of the experimental data with Kamlet-Taft solvatochromic parameters is employed.     

BMIMPF_6-有机溶剂对聚噻吩电化学性能的影响

实验测试了纯离子液体BMIMPF6、BMIMPF6-乙腈、BMIMPF6-碳酸丙二醇脂混合体系的粘度和电导率.应用循环伏安法在玻碳电极表面合成了聚噻吩,并测试了聚噻吩修饰电极在上述各溶液中的电化学行为.结果表明,聚噻吩在纯离子液体中的惨杂电量较小,电化学反应的可逆性较差.聚噻吩的氧化参杂电量与混合溶液的电导率呈明显的线性关系,当离子液体的体积含量为25%时,溶液的电导率达到最大,同时聚噻吩惨杂电量也达到最大,反应可逆也得到了明显的改善.     

Trace analysis of complex organic mixtures using capillary gas-liquid chromatography and the dynamic solvent effect

A sampling system for high resolution gas-liquid chromatography, based on the dynamic solvent effect, is described. Volatiles are accumulated off-line in a concentrator/injector and delivered to the column using an on-line inlet. Volatiles may be accumulated from gaseous or liquid matrices; they may be transferred to these by gas sparging or solvent extraction of any type of sample. The sampling technique is quantitatively precise; e.g. coefficients of variation of peak percentage areas better than 5% for a range of solutes at a concentration of 2:10⁷. Examples of the application of the sampling system are presented.     

Influence of temperature on peak shape and solvent compatibility: implications for two-dimensional liquid chromatography

Solvent compatibility is a limiting factor for the success of two-dimensional liquid chromatography (2-D LC). In the second dimension, solvent effects can result in overpressures as well as in peak broadening or even distortion. A peak shape study was performed on a one-dimensional high-performance liquid chromatography (HPLC) system to simulate the impact of peak distorting solvent effects on a reversed-phase second dimension separation operated at high temperatures. This study includes changes in injection volume, solute concentration, column inner diameter, eluent composition and oven temperature. Special attention was given to the influence of high temperatures on the solvent effects. High-temperature HPLC (HT-HPLC) is known to enhance second dimension separations in terms of speed, selectivity and solvent compatibility. The ability to minimise the viscosity contrast between the mobile phases of both dimensions makes HT-HPLC a promising tool to avoid viscosity mismatch effects like (pre-)viscous fingering. In case of our study, viscosity mismatch effects could not be observed. However, our results clearly show that the enhancement in solvent compatibility provided by the application of high temperatures does not include the elimination of solvent strength effects. The additional peak broadening and distortion caused by this effect is a potential error source for data processing in 2-D LC.     

Concentration of volatile organic compounds from solvents by sustained chromatographic evaporation

A system for quantitative concentration of volatile organic trace compounds present in organic solvents is described. Evaporation of the solvent is carried out inside a glass capillary tube by the action of a carrier gas, and large volumes can be reduced by a repeated sample injection and a cyclic flow reversal. Best recovery is obtained when a barrier of pure solvent is maintained ahead of the sample during concentration. Four rotary valves are employed for sample and solvent injection and direction of the gas flow. In principle, indefinite sample volumes can be handled, the limit being set by system contaminants. The process was evaluated both off-line and on-line to a gas chromatograph. Concentration of compounds like methylcyclopentane, hexane, and cyclohexane present in pentane in the low nanogram range and subsequent on-line transfer to a gas chromatograph could be performed with a quantitative recovery. The technique was applied to analysis of trace volatiles in drinking water. Detection limits were estimated to be approximately 0.02 ng/L for normal hydrocarbons (FID detection) when concentration of a pentane extract from a one litre water sample was carried out.     

An ionic liquid as a solvent for headspace single drop microextraction of chlorobenzenes from water samples

A headspace single-drop microextraction (HS-SDME) procedure using room temperature ionic liquid and coupled to high-performance liquid chromatography capable of quantifying trace amounts of chlorobenzenes in environmental water samples is proposed. A Plackett-Burman design for screening was carried out in order to determine the significant experimental conditions affecting the HS-SDME process (namely drop volume, aqueous sample volume, stirring speed, ionic strength, extraction time and temperature), and then a central composite design was used to optimize the significant conditions. The optimum experimental conditions found from this statistical evaluation were: a 5 μL microdrop of 1-butyl-3-methylimidazolium hexafluorophosphate, exposed for 37 min to the headspace of a 10 mL aqueous sample placed in a 15 mL vial, stirred at 1580 rpm at room temperature and containing 30% (w/v) NaCl. The calculated calibration curves gave a high level of linearity for all target analytes with correlation coefficients ranging between 0.9981 and 0.9997. The repeatability of the proposed method, expressed as relative standard deviation, varied between 1.6 and 5.1% (n = 5). The limits of detection ranged between 0.102 and 0.203 μg L⁻¹. Matrix effects upon extraction were evaluated by analysing spiked tap and river water as well as effluent water samples originating from a municipal wastewater treatment plant.     

Molecularly imprinted silica prepared with immiscible ionic liquid as solvent and porogen for selective recognition of testosterone

1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF₄), an ionic liquid (IL) immiscible with water, was used as a new type of solvent and porogen for the preparation of molecularly imprinted silica. The new imprinted silica was prepared by a sacrificial spacer molecular imprinting approach with testosterone as template molecule. The new covalent monomer-template complex used in the imprinting procedure was synthesized via the reaction of 3-(triethoxysilyl)propyl isocyanate with testosterone. The imprinted silica was characterized by FT-IR spectroscopy, N₂ gas adsorption–desorption isotherm and the high-resolution transmission electron microscopy. Moreover, the selective adsorption ability of the imprinted particles towards testosterone was investigated by the steady-state binding experiment with testosterone propionate as its structural analogue. Results showed that the imprinted silica obtained in this study had relatively homogenous structure with numerous mesopores, indicating that the IL used here is an excellent solvent and satisfactory porogen for the preparation of imprinted materials. Moreover, ILs are more environmentally friendly than traditional organic solvents due to their negligible vapor pressure. The imprinted silica possesses highly specific recognition property and high binding capacity towards testosterone, showing that the new imprinting technique is relatively successful.     

Extraction of organic compounds with room temperature ionic liquids

Room temperature ionic liquids are novel solvents with a rather specific blend of physical and solution properties that makes them of interest for applications in separation science. They are good solvents for a wide range of compounds in which they behave as polar solvents. Their physical properties of note that distinguish them from conventional organic solvents are a negligible vapor pressure, high thermal stability, and relatively high viscosity. They can form biphasic systems with water or low polarity organic solvents and gases suitable for use in liquid–liquid and gas–liquid partition systems. An analysis of partition coefficients for varied compounds in these systems allows characterization of solvent selectivity using the solvation parameter model, which together with spectroscopic studies of solvent effects on probe substances, results in a detailed picture of solvent behavior. These studies indicate that the solution properties of ionic liquids are similar to those of polar organic solvents. Practical applications of ionic liquids in sample preparation include extractive distillation, aqueous biphasic systems, liquid–liquid extraction, liquid-phase microextraction, supported liquid membrane extraction, matrix solvents for headspace analysis, and micellar extraction. The specific advantages and limitations of ionic liquids in these studies is discussed with a view to defining future uses and the need not to neglect the identification of new room temperature ionic liquids with physical and solution properties tailored to the needs of specific sample preparation techniques. The defining feature of the special nature of ionic liquids is not their solution or physical properties viewed separately but their unique combinations when taken together compared with traditional organic solvents.