Flow-Assisted Synthesis of Bicyclic Aziridines <i>via</i> Photochemical Transformation of Pyridinium Salts

Herein is described the development and comparison of homemade continuous-flow reactors, a fluorinated ethylene propylene tube (FEP) reactor (internal diameter of 0.4 cm) and two parallel quartz reactors containing two different internal diameters (0.4 and 0.2 cm), and their application to the photochemical transformation of 1-<i>n</i>-butyl- and 1-allylpyridinium bromide salts (<b>1a</b> and <b>1b</b>, respectively) to the corresponding α-hydroxycyclopentenoaziridines (6-azabicyclo[3.1.0]­hex-3-en-2-ols) <b>2a</b> and <b>2b</b>. Under recirculating conditions, the FEP reactor allowed the production of a greater quantity of bicyclic aziridine (3.2 g), while the quartz reactor with the same diameter furnished the best productivity results (3.7 g L^–1 h^–1). In addition, the FEP reactor operated efficiently under circulating conditions (1.75 L of <b>1a</b>) for 4.5 days (residence time of 17.9 h), allowing the production of <b>2a</b> at a rate of 2 g/day (62–93% conversion)

Copper(II) Triflate As a Reusable Catalyst for the Synthesis of <i>trans</i>-4,5-Diamino-cyclopent-2-enones in Water

<i>trans</i>-4,5-Diamino-cyclopent-2-enones (CP) are usually prepared by Lewis acid-catalyzed condensation of furfural and a secondary amine in an organic solvent. The reaction proceeds through the formation of a Stenhouse salt (SS) intermediate followed by an electrocyclization reaction to afford the desired CP. Herein, we described the use of Cu­(OTf)₂ as a very efficient catalyst for the synthesis of CP in water at room temperature. Furthermore, the mild reaction conditions, catalyst reusability, and outstanding functional group tolerance suggest that this CP platform can be further used in chemical biology

Supported Ionic Liquid Membranes for Removal of Dioxins from High-Temperature Vapor Streams

Dioxins and dioxin-like chemicals are predominantly produced by thermal processes such as incineration and combustion at concentrations in the range of 10–100 ng of I-TEQ/kg (I-TEQ = international toxic equivalents). In this work, a new approach for the removal of dioxins from high-temperature vapor streams using facilitated supported ionic liquid membranes (SILMs) is proposed. The use of ceramic membranes containing specific ionic liquids, with extremely low volatility, for dioxin removal from incineration sources is proposed owing to their stability at very high temperatures. Supported liquid membranes were prepared by successfully immobilizing the ionic liquids tri-C₈–C₁₀-alkylmethylammonium dicyanamide ([Aliquat][DCA]) and 1-<i>n</i>-octyl-3-methylimidazolium dicyanamide ([Omim][DCA]) inside the porous structure of ceramic membranes. The porous inorganic membranes tested were made of titanium oxide (TiO₂), with a nominal pore size of 30 nm, and aluminum oxide (Al₂O₃), with a nominal pore size of 100 nm. The ionic liquids were characterized, and the membrane performance was assessed for the removal of dioxins. Different materials (membrane pore size, type of ionic liquid, and dioxin) and different operating conditions (temperature and flow rate) were tested to evaluate the efficiency of SILMs for dioxin removal. All membranes prepared were stable at temperatures up to 200 °C. Experiments with model incineration gas were also carried out, and the results obtained validate the potential of using ceramic membranes with immobilized ionic liquids for the removal of dioxins from high-temperature vapor sources

Organocatalyzed One-Step Synthesis of Functionalized <i>N-</i>Alkyl-Pyridinium Salts from Biomass Derived 5‑Hydroxymethylfurfural

An efficient and scalable method has been developed for the synthesis of <i>N-</i>alkylpyridinium salts from biomass derived 5-hydroxymethyl­furfural and alkyl amines using a catalytic amount of formic acid. This protocol is also extended to various diamines providing the exclusive formation of mono-<i>N-</i>alkylpyridinium salts. In addition, the mechanism for the formation of pyridinium salts was studied by DFT and using H₂¹⁸O isotope labeled experiments showing no incorporation of ¹⁸O in the product

Excited-State Proton Transfer of Fluorescein Anion as an Ionic Liquid Component

Fluorescent ionic liquids (FILs) incorporating the fluorescein anion have been prepared by anion exchange of the parent quaternary ammonium chloride (Quat⁺Cl^–) ionic liquid. By controlling the molar ratio of fluorescein to Quat⁺Cl^–, ionic liquids incorporating different prototropic forms of fluorescein were prepared. The 1:1 molar ratio ionic liquid (FIL1) is essentially composed of monoanionic fluorescein, while dianionic fluorecein is predominant in the FIL with a 1:2 molar ratio (FIL2). The fluorescence excitation spectrum of FIL2 is markedly different from its absorption spectrum. Absorption features the fluorescein dianion, while the excitation spectrum is exclusively due to the monoanion. In FIL1, the absorption and excitation spectra are both characteristic of the monoanion. In both FILs, emission of the dianion is observed upon excitation of the monoanion. This unusual behavior is interpreted in the context of a fast deprotonation of the monoanion in the excited state. The presence of residual water in the ionic liquid is important for the proton transfer process. By lowering the pH of FIL1, the transient proton transfer is inhibited, and the emission of the monoanion could be observed. The FILs have completely different spectroscopic properties from solvated fluorescein in Quat⁺Cl^–, where the prototropic equilibrium is shifted toward the neutral forms

¹H NMR Relaxometry and Diffusometry Study of Magnetic and Nonmagnetic Ionic Liquid-Based Solutions: Cosolvent and Temperature Effects

In this work, ¹H NMR relaxometry and diffusometry as well as viscometry experiments were carried out as a means to study the molecular dynamics of magnetic and nonmagnetic ionic liquid-based systems. In order to evaluate the effect of a cosolvent on the superparamagnetic properties observed for Aliquat-iron-based magnetic ionic liquids, mixtures comprising different concentrations, 1% and 10% (v/v), of DMSO-<i>d</i>6 were prepared and studied. The results for both magnetic and nonmagnetic systems were consistently analyzed an suggest that, when at low concentrations, DMSO-<i>d</i>6 promotes more structured ionic arrangements, thus enhancing these superparamagnetic properties. Furthermore, the analysis of temperature and water concentration effects allowed to conclude that neither one of these variables significantly affected the superparamagnetic properties of the studied magnetic ionic liquids

Developments in the Reactivity of 2‑Methylimidazolium Salts

Unexpected and unusual reactivity of 2-methylimidazolium salts toward aryl-<i>N</i>-sulfonylimines and aryl aldehydes is here reported. Upon reaction with aryl-<i>N</i>-sulfonylimines, the addition product, arylethyl-2-imidazolium-1-tosylamide (<b>3</b>), is formed with moderate to good yields, while upon reaction with aldehydes, the initial addition product (<b>6</b>) observed in NMR and HPLC–MS experimental analysis is postulated by us as an intermediate to the final conversion to carboxylic acids. Studies in the presence and absence of molecular oxygen allow us to conclude that the imidazolium salts is crucial for the oxidation. A detailed mechanistic study was carried out to provide insights regarding this unexpected reactivity