Efficient α‐Chlorination of Aryl Ketones Using Aluminum Chloride/Urea–Hydrogen Peroxide in Ionic Liquid

Effective α‐chlorination reactions of aryl ketones into the corresponding α‐chloroketones have been accomplished with aluminum chloride hexahydrate and urea–hydrogen peroxide in [bmim]BF₄ ionic liquid.     

Nitrile-Promoted Alkene Epoxidation with Urea–Hydrogen Peroxide (UHP)

An efficient method for alkene epoxidation has been studied systematically using benzonitrile and the complex urea–hydrogen peroxide (UHP), which is an anhydrous form of hydrogen peroxide and has the potential to release hydrogen peroxide in a controlled manner and thus avoid the need to slowly add aqueous H₂O₂ to the reaction mixture. The absence of water in the reaction media was also beneficial, because it minimized undesired reactions of the oxidized products. A range of alkenes was epoxidized by this method, providing yields ranging from 79% to 96%.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Ytterbium(III) Triflate–Catalyzed Stereoselective Synthesis of β‐Lactams via [2+2] Cyclocondensation in Ionic Liquid

Catalyzed by ytterbium(III) triflate [Yb(OTf)₃], β‐lactams were stereoselectively synthesized from imines and acetyl chlorides in ionic liquid under mild conditions. The ionic liquid and catalyst could be recycled and reused as opposed to traditional solvent–catalyst systems.     

C–C Bond Rupture in the Oxidation of Lower (C2–C6) Alcohols with Hydrogen Peroxide Mediated by Iron-Containing Compounds

C–C bond rupture upon the oxidation of alcohols in the Fe(ClO₄)₃+ H₂O₂system in aqueous acetonitrile at room temperature is found. The relative yield of the products of C–C bond rupture is 20–30% under standard conditions for C₂and C₃alcohols and decreases in the series C₂> C₃> C₄> C₆. The alkyl radical and carboxylic acid are the products of C–C bond rupture in alcohol oxidation. Cyclohexane is a competitive inhibiting agent for C–H bond oxidation in 1-propanol, and it does not affect the yield of the products of C–C bond rupture. When H₂O₂is replaced by tert-BuOOH, the fraction of the products of C–C bond rupture decreases by an order of magnitude. Our data suggest that a non-radical intermediate, likely Fe(III) hydroperoxo complex, is responsible for C–C bond rupture in alcohol under the reaction conditions.     

Room-Temperature Oxidation of Secondary Alcohols by Bromate–Bromide Coupling in Acidic Water

Abstract

The use of environmentally benign reactions is currently an important topic in the field of synthetic chemistry. Here we report a high-yielding method to oxidize aliphatic or aromatic secondary alcohols into corresponding ketones using nonhazardous and inexpensive BrOH reagent at room temperature in water. BrOH reagent was derived from NaBr and NaBrO₃ in aqueous acid. Based on the presented results, a mechanism was proposed for this oxidation. The reported method offers a facile, efficient procedure to produce various ketones with a low amount of side products.     

Useful Application of Acidic Ionic Liquids as Solvents in Baeyer–Villiger Oxidation with Hydrogen Peroxide for the Synthesis of Lactones

Cyclic ketones have been efficiently oxidized with hydrogen peroxide using acidic ionic liquids (ILs) as solvents. This is a new method for the synthesis of lactones with high yields that does not utilize any additional catalysts and enables ILs to be recycled.     

Ethylene and Cyclohexene Oxidation by p-Benzoquinone,Hydrogen Peroxide,and Oxygen in the Solutions of Cationic Pd(II) Complexes in Acetonitrile–Water and Ionic Liquid–Water Binary Solvents

Kinetics and Catalysis - Optimal conditions are selected for ethylene and cyclohexene oxidation reactions in the acetonitrile (AN)–water system in the presence of...     

Efficient Procedure for Oxidation of Benzylic Alcohols to Carbonyl Compounds by N‐Bromosuccinimide in Ionic Liquid

Abstract

Efficient oxidation of various benzylic alcohols to the corresponding carbonyl compounds has been achieved in the presence of NBS and 2,6‐lutidine in ionic liquid [bmim]BF₄.     

Efficient and Rapid Method for the Oxidation of Electron‐Rich Aromatic Aldehydes to Carboxylic Acids Using Improved Basic Hydrogen Peroxide

An efficient and rapid method for oxidation of electron‐rich aromatic aldehydes to their corresponding carboxylic acids in excellent yields was developed. It is based on the oxidation of methoxy‐substituted benzaldehydes in methanol with an improved aqueous basic hydrogen peroxide system. Benzaldehydes with electron‐withdrawing substituents are oxidized to the corresponding carboxylic acid in excellent yields under mild reaction conditions.     

Urea–Hydrogen Peroxide Complex: A Selective Oxidant in the Synthesis of 2-Phenylselenyl-1,3-butadienes

2-Phenylselenyl-1,3-butadienes were synthesized via the selective oxidation of 2,4-diphenylselenyl-1-butenes with urea–hydrogen peroxide followed by the selenoxide elimination.     

Determination of Tetracyclines in Milk,Eggs and Honey Using in-situ Ionic Liquid Based Dispersive Liquid–Liquid Microextraction

In this study, in-situ ionic liquid based dispersive liquid?liquid microextraction method for enrichment of tetracyclines before liquid chromatographic analysis has been improved. A 1-benzyl-3- methylimidazolium chloride was used as an ionic liquid. To increase extraction efficiency, some optimization parameters (amount of ammonium hexafluorophoshate, extraction time, centrifugation time, ratio of ionic liquid/salt) were investigated. At optimized conditions, enrichment factors of four tetracycline antibiotics (tetracycline, chlortetracycline, methacycline, doxycycline) were between 25 and 98. The residues of tetracyclines were not found in the studied real samples. For the accuracy of the method, the concentration of 50 and 250 μg/L of standard tetracycline mixture solutions were spiked to the blank real milk, honey and egg samples and the percentage recoveries were obtained in the range of 75.8–109.7%.     

Determination of Cadmium in Human Serum and Blood Samples after Dispersive Liquid–Liquid Microextraction Using a Task-Specific Ionic Liquid

Task-specific ionic liquid dispersive liquid–liquid microextraction (TSIL-DLLME) is a simple and rapid preconcentration approach for the measurement of cadmium in serum and blood samples of human subjects. In this method a novel task-specific ionic liquid, trioctylmethyl ammonium thiosalicylate (TOMATS), which has dual characteristics as a chelating agent and extractive solvent, was investigated. TOMATS complexes with Cd due to the chelating effect of the ortho-positioned carboxylate relative to the thiol functionality. The assessment of the optimum values of variables including the pH, amount of reagents (TOMATS, diluents, Triton X114, and back extracting acid solution), temperature, and incubation time, which affect the recoveries of analyte by TSIL-DLLME method were studied. After enrichment experiments, acidic solution was used to back extract the metal ions from the ionic liquid rich phase and with determination by electrothermal atomic absorption spectrometry. Using the optimal experimental conditions, the limit of detection (3?s), precision (relative standard deviation), preconcentration, and enhancement factors of developed method for Cd were found to be 0.05?µg/L, greater than 5%, 62.5, and 52.8, respectively. To check the accuracy of the developed method, certified reference material of serum and blood were analyzed by the developed method, and the measured values of Cd were in good agreement with the certified values. The developed method was applied successfully to determine Cd in blood and serum samples of lymphatic cancer patients relative to healthy controls.     

Mild and Convenient Synthesis of 1,2‐Dihydroquinolines from Anilines and Acetone Catalyzed by Ytterbium(III) Triflate in Ionic Liquids

A mild, convenient, and efficient process has been developed for the synthesis of 2,2,4‐trimethyl‐1,2‐dihydroquinolines by the reaction of anilines with acetone catalyzed by ytterbium(III) triflate [Yb(OTf)₃] in ionic liquids. The catalyst and ionic liquids can be easily recovered and reused, making this method friendly and environmentally acceptable.     

[α‐PW12O40]3− Immobilized on Ionic Liquid–Modified Polymer as a Heterogeneous Catalyst for Alcohol Oxidation with Hydrogen Peroxide

Ionic liquid–modified polystyrene resin beads were demonstrated to be an appropriate support for polyoxometalate. In this heterogeneous catalytic system, alcohols can be efficiently oxidized to corresponding carbonyl groups with H₂O₂ in CH₃CN. The catalyst can be easily recovered by filtration and recycled without apparent loss of catalytic performance.     

Kinetics and Mechanism of 2,3,6-Trimethylphenol Oxidation by Hydrogen Peroxide in the Presence of TiO2–SiO2 Aerogel

The product and kinetics studies of 2,3,6-trimethylphenol (TMP) oxidation by 30% aqueous ₂₂ in the presence of a heterogeneous catalyst, TiO₂–SiO₂ aerogel, are performed in an MeCN medium. The main reaction products are 2,3,5-trimethyl-1,4-benzoquinone and 2,2",3,3",6,6"-hexamethyl-4,4"-biphenol. The reaction is first-order in ₂₂ and fractional order (1–0) in TMP. The reaction rate is proportional to the catalyst amount and depends on the water concentration in the reaction mixture in a complex manner. The results suggest the formation of an active intermediate on the titanium center. In this intermediate containing both a TMP molecule and the hydroperoxide group, inner-sphere one-electron oxidation of TMP occurs to give the phenoxyl radical.     

Immobilization of Pd(II) Catalysts for Cyclopropanation in Ionic Liquid

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Using Partial Least-Squares Regression in Multivariate UV Spectroscopic Analysis of Mixtures of Imidazolium-Based Ionic Liquids and 1-Methylimidazole for Measurements of Liquid–Liquid Equilibria

Recent interest in the use of room-temperature ionic liquids in various industrial applications sets requirements for analytical techniques that could lead to an efficient determination of concentrations of ionic liquids and/or possible impurities contained in them. Catalytic processes are particularly sensitive to the amount of impurities in the reaction media. Finding suitable and efficient techniques of determining compositions of liquid mixtures appears to be of importance not only for the design and optimization of such catalytic processes but also in measurements of phase equilibria. Imidazolium-based ionic liquids are often contaminated by their precursors 1-chlorobutane and 1-methylimidazole. Therefore, in this work a calibration technique is proposed that makes use of partial least-squares regression in UV spectroscopic determination of concentrations of 1-butyl-3-methylimidazolium hexafluorophosphate and 1-methylimidazole. Spectra of these compounds show significant overlaps making their simultaneous quantitative analysis difficult. Partial least-squares regression using the PLS2 algorithm provides an effective resolution, decomposing complicated spectra and coping with component interferences, nonlinearities and collinearity. The calibration method for the chosen compounds was validated using test samples of known composition and by measuring liquid?Cliquid equilibria at 298.15?K in the ternary system 1-butyl-3-methylimidazolium hexafluorophosphate?+?1-methylimidazole?+?1-chlorobutane.     

Rapid Determination of DDT and Its Metabolites in Environmental Water Samples with Mixed Ionic Liquids Dispersive Liquid–Liquid Microextraction Prior to HPLC-UV

In this paper, a novel mixed ionic liquids-dispersive liquid–liquid microextraction method was developed for rapid enrichment and determination of environmental pollutants in water samples. In this method, two kinds of ionic liquids, hydrophobic ionic liquid and hydrophilic ionic liquid, were used as extraction solvent and disperser solvent, respectively. DDT and its metabolites were used as model analytes and high-performance liquid chromatography with ultraviolet detector for the analysis. Factors that may affect the extraction recoveries, such as type and volume of extraction solvent (hydrophobic ionic liquid) and disperser solvent (hydrophilic ionic liquid), extraction time, sample pH and ionic strength, were investigated and optimized. Under the optimum conditions, the linear range was 1–100 μg L⁻¹, limits of detection could reach 0.21–0.49 μg L⁻¹, and relative standard deviation was 6.01–8.48 % (n = 7) for the analytes. Satisfactory results were achieved when the method was applied to analyze the target pollutants in environmental water samples with spiked recoveries over the range of 85.7–106.8 %.