7 research outputs found
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]Âhex-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<sup>â1</sup> h<sup>â1</sup>). 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 (62â93% 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 CuÂ(OTf)<sub>2</sub> 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 10â100 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-C<sub>8</sub>âC<sub>10</sub>-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 (TiO<sub>2</sub>), with a nominal pore size of 30 nm, and aluminum oxide (Al<sub>2</sub>O<sub>3</sub>), 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 5âHydroxymethylfurfural
An efficient and scalable method
has been developed for the synthesis
of <i>N-</i>alkylpyridinium salts from biomass derived 5-hydroxymethylÂfurfural
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 H<sub>2</sub><sup>18</sup>O isotope labeled experiments
showing no incorporation of <sup>18</sup>O 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<sup>+</sup>Cl<sup>â</sup>) ionic liquid.
By controlling the molar ratio of fluorescein to Quat<sup>+</sup>Cl<sup>â</sup>, 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<sup>+</sup>Cl<sup>â</sup>, where the prototropic equilibrium is shifted toward the neutral
forms
<sup>1</sup>H NMR Relaxometry and Diffusometry Study of Magnetic and Nonmagnetic Ionic Liquid-Based Solutions: Cosolvent and Temperature Effects
In
this work, <sup>1</sup>H 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 2âMethylimidazolium 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 HPLCâMS 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