Application of ionic liquids in organic reactions

Room-temperature ionic liquids are good solvents for a wide of organic, inorganic and organometallic compounds. Typically consisting of nitrogen-containing organic cations and inorganic anions, they are easy to recycle, nonflammable, and have no detectable vapor pressure. More recently, ionic liquids have been found to be excellent solvents for a number of chemical reactions, e. g. hydrogenation, alkylation, epoxidation, Heck-vinylation, Suzuki cross-coupling reactions and enzyme catalyzed organic reactions. This paper focuses on the recent development of using ionic liquids as solvents for transition metal and enzyme catalyzed reactions.

Amperometric quantification of polar organic solvents based on a tyrosinase biosensor

A novel amperometric biosensor for quantification of the electrochemically inert polar organic solvents based on tyrosinase electrode was preliminarily reported. The biosensor was fabricated by simply syringing an aqueous solution of tyrosinase/PVAVP (PVAVP: copolymer of poly(vinyl alcohol) grafting with 4-vinylpyridine) onto glassy carbon electrode surface followed by drying the modified electrode at +4 degrees C in a refrigerator. The current generated from electrochemical reduction of quinone is a probe signal. The biosensor can be used for quantification of polar organic solvents, and its mechanism was characterized with in situ steady-state amperometry-quartz crystal microbalance experiments. The detection limit, sensitivity, and dynamic range for certain organic solvents are dependent on the kind and concentration of the substrate probe and the hydrophobicity of the immobilization matrix. The response time for all the tested organic solvents is less than 2 min.

Chain conformation of a high-performance polyimide in organic solution

An organo-soluble polyimide based on 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and 2,2'dimethyl-4,4'-methylene dianiline (DMMDA), was synthesized via two-step polycondensation accompanied by chemical imidization. Five fractions were prepared by fractionation. The dilute solutions of the fractions were studied by LLS (Laser Light Scattering) and the intrinsic viscosities of the fractions were measured. The unperturbed dimension was determined by the intrinsic viscosity with the Stockmayer-Fox equation. The results indicate that the polyimide in this study has a flexible chain conformation in chloroform and N,N-dimethyl acetamide (DMAc). However, the degree of chain expansion differs in different solvents. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

ELECTROCHEMICAL INVESTIGATION OF LIQUID/LIQUID SYSTEMS USING VARIOUS ORGANIC SOLVENTS

The potential windows of the system water/pure solvent (W/P) and water/solvent mixtures(W/S) have been investigated by cyclic voltammetry with solvents whose dielectric constants lie between 5.87 and 34.82. In the presence of LiCI in the aqueous phase and tetrabutytammoniumtetraphenylborate(TBATPB) in the organic phase, the systems water/allyl iso-thiocyanate (W/AIT) and water/nitrobensene (W/NB) show a same wide epotential window. thermodynamic parameters of ion transfer W/AIT interface were determined. In systems of W/P and V/S the influence solvent effect on the standard gibbs energies of transfer of was discussed.

Retrospective assessment of dryland soil stability in relation to grazing and climate change

Accelerated soil erosion is an aspect of dryland degradation that is affected by repeated intense drought events and land management activities such as commercial livestock grazing. A soil stability index (SSI) that detects the erosion status and susceptibility of a landscape at the pixel level, i.e., stable, erosional, or depositional pixels, was derived from the spectral properties of an archived time series (from 1972 to 1997) of Landsat satellite data of a commercial ranch in northeastern Utah. The SSI was retrospectively validated with contemporary field measures of soil organic matter and erosion status that was surveyed by US federal land management agencies. Catastrophe theory provided the conceptual framework for retrospective assessment of the impact of commercial grazing and soil water availability on the SSI. The overall SSI trend was from an eroding landscape in the early drier 1970s towards stable conditions in the wetter mid-1980s and late 1990s. The landscape catastrophically shifted towards an extreme eroding state that was coincident with the “The Great North American Drought of 1988”. Periods of landscape stability and trajectories toward stability were coincident with extremely wet El Niño events. Commercial grazing had less correlation with soil stability than drought conditions. However, the landscape became more susceptible to erosion events under multiple droughts and grazing. Land managers now have nearly a year warning of El Niño and La Niña events and can adjust their management decisions according to predicted landscape erosion conditions.

Rate acceleration of the Baylis-Hillman reaction in polar solvents (water and formamide). Dominant role of hydrogen bonding, not hydrophobic effects, is implicated

A substantial acceleration of the Baylis-Hillman reaction between cyclohexenone and benzaldehyde has been observed when the reaction is conducted in water. Several different amine catalysts were tested, and as with reactions conducted in the absence of solvent, 3-hydroxyquinuclidine was found to be the optimum catalyst in terms of rate. The reaction has been extended to other aldehyde electrophiles including pivaldehyde. Attempts to extend this work to acrylates was only partially successful as rapid hydrolysis of methyl and ethyl acrylates occurred under the base-catalyzed and water-promoted conditions. However, tert-butyl acrylates were sufficiently stable to couple with relatively reactive electrophiles. Further studies on the use of polar solvents revealed that formamide also provided significant acceleration and the use of 5 equiv of formamide (optimum amount) gave faster rates than reactions conducted in water. Using formamide, further acceleration was achieved in the presence of Yb(OTf)(3) (5 mol %). The scope of the new conditions was tested with a range of Michael acceptors and benzaldehyde and with a range of electrophiles and ethyl acrylate. The origin of the rate acceleration is discussed.

Development and application of NMR techniques to study water-in-CO2 microemulsions

Self-assembly is a phenomenon that occurs frequently throughout the universe. In this work, two self-assembling systems were studied: the formation of reverse micelles in isooctane and in supercritical CO2 (scCO2), and the formation of gels in organic solvents. The goal was the physicochemical study of these systems and the development of an NMR methodology to study them. In this work, AOT was used as a model molecule both to comprehensively study a widely researched system water/AOT/isooctane at different water concentrations and to assess its aggregation in supercritical carbon dioxide at different pressures. In order to do so an NMR methodology was devised, in which it was possible to accurately determine hydrodynamic radius of the micelle (in agreement with DLS measurements) using diffusion ordered spectroscopy (DOSY), the micellar stability and its dynamics. This was mostly assessed by 1H NMR relaxation studies, which allowed to determine correlation times and size of correlating water molecules, which are in agreement with the size of the shell that interacts with the micellar layer. The encapsulation of differently-sized carbohydrates was also studied and allowed to understand the dynamics and stability of the aggregates in such conditions. A W/CO2 microemulsion was prepared using AOT and water in scCO2, with ethanol as cosurfactant. The behaviour of the components of the system at different pressures was assessed and it is likely that above 130 bar reverse microemulsions were achieved. The homogeneity of the system was also determined by NMR. The formation of the gel network by two small molecular organogelators in toluene-d8 was studied by DOSY. A methodology using One-shot DOSY to perform the spectra was designed and applied with success. This yielded an understanding about the role of the solvent and gelator in the aggregation process, as an estimation of the time of gelation.

Strong hydrogen bonding in organic synthesis

The preparation of phenacyl and para-phenylphenacyl esters, the reactions of carboxylic acids, phenols, 2-nitropropane and alcohols with alkyl halides in the presence of fluoride anion are described. The reactions are thought to be accelerated by the formation of hydrogen bonds between the fluoride anion and the organic electron acceptor. The fluoride ,carboxylic acids, fluoride-phenols and fluoride-2-nitropropane are better reaction systems than the fluoride-alcohol. The source of the fluoride anion and the choice of solvents are also discussed.

Organic solvents as risk factor for autoimmune diseases: a systematic review and meta-analysis

Background: Genetic and epigenetic factors interacting with the environment over time are the main causes of complex diseases such as autoimmune diseases (ADs). Among the environmental factors are organic solvents (OSs), which are chemical compounds used routinely in commercial industries. Since controversy exists over whether ADs are caused by OSs, a systematic review and meta-analysis were performed to assess the association between OSs and ADs. Methods and Findings: The systematic search was done in the PubMed, SCOPUS, SciELO and LILACS databases up to February 2012. Any type of study that used accepted classification criteria for ADs and had information about exposure to OSs was selected. Out of a total of 103 articles retrieved, 33 were finally included in the meta-analysis. The final odds ratios (ORs) and 95% confidence intervals (CIs) were obtained by the random effect model. A sensitivity analysis confirmed results were not sensitive to restrictions on the data included. Publication bias was trivial. Exposure to OSs was associated to systemic sclerosis, primary systemic vasculitis and multiple sclerosis individually and also to all the ADs evaluated and taken together as a single trait (OR: 1.54; 95% CI: 1.25-1.92; p-value, 0.001). Conclusion: Exposure to OSs is a risk factor for developing ADs. As a corollary, individuals with non-modifiable risk factors (i.e., familial autoimmunity or carrying genetic factors) should avoid any exposure to OSs in order to avoid increasing their risk of ADs.

The behaviour of organic solvents containing C5-BTBP and CyMe4-BTBP at low irradiation doses

Low doses of gamma radiation were given to four different solvents containing C5-BTBP and CyMe4-BTBP, each molecule dissolved both in cyclohexanone and hexanol. Four corresponding solvents were kept unirradiated and used as references for the extraction experiments. Multiple samples were taken from both the irradiated solutions and the reference solutions at certain time intervals. The samples were used in extraction experiments with the radionuclides Am-241 and Eu-152. The protection against radiolysis of the extracting molecules by the diluent used for dissolution without adding a scavenger molecule was checked. The interplay between the diluent and the side group of the extracting molecule for protection against radiolysis was also studied by keeping the same type of core molecule for binding to the metal ions and varying the diluent and side group. The results were unexpected. The presence of a cyclic molecule as both a side group or diluent seems to keep the extraction of europium almost unaffected by radiolysis, while americium behaves differently from solvent to solvent. The diluent alone does not protect the extracting molecule. In some of the studied systems there is a distinct change in the extraction behaviour of Am between the irradiated and reference solutions, an effect that is however only present at the beginning of the experimental series. At later times the difference in distribution ratios between the irradiated and reference solution is constant. This phenomenon is found only when the side group and diluent are structurally dissimilar.

Anion recognition and sensing in organic and aqueous media using luminescent and colorimetric sensors

This review article focuses primarily on the work carried in our laboratories over the last few years using luminescent and colorimetric sensors, where the anion recognition occurs through hydrogen bonding in organic or aqueous solvents. This review begins with the story of the discovery of fluorescent photoinduced electron transfer (PET) sensors for anions using charged neutral urea or thiourea receptors where both fluorescent and NMR spectroscopic methods monitored anion recognition. This work led to the development of dual luminescent and colorimetric anion sensors based on the use of the ICT based naphthalimide chromophore, where ions such as fluoride gave rise to changes in both the fluorescence and the absorption spectra of the sensors, but at different concentrations. Here, the former changes were due to hydrogen bonding interactions, whereas the latter was due to the deprotonation of acidic protons, giving rise to the formation of the bifluoride anion (HF2−). Modification of the 4-amino-l,8-naphthalimide moiety has facilitated the formation of colorimetric anion sensors that work both in organic or aqueous solutions. Such charge neutral receptor motifs have also been incorporated into organic scaffolds with norbomyl and calixarene backbones, which have enabled us to produce anion directed self-assembled structures.

Physical trends and structural features in organic salts of the thiocyanate anion

A new series of ionic liquids based on the thiocyanate anion has been prepared. Incorporation of this anion with an imidazolium, tetraalkylammonium or pyrrolidinium cation produces ionic liquids with advantageously low melting points and good thermal stability. The low temperature phase behaviour of the salts has been investigated using differential scanning calorimetry and multiple solid phases have been observed. The electrochemical windows of representative imidazolium and pyrrolidinium species have been investigated by cyclic voltammetry and determined to be 2.4 and 3.5 V, respectively. In addition, the solid-state structure of N,N-dimethylpyrrolidinium thiocyanate has been determined by X-ray crystallography. This is the first reported structure of a pyrrolidinium thiocyanate species and shows a layered structure with linear thiocyanate groups having bond lengths comparable to those observed in similar SCN−-containing species.

Enzymatic synthesis of isopropyl acetate catalysed by immobilized bacillus cereus lipase in organic medium

Selective production of fragrance fatty acid ester from isopropanol and acetic acid has been achieved using silica-immobilizedlipase of Bacillus cereus MTCC 8372. A purified thermoalkalophilic extracellular lipase was immobilized by adsorption onto the silica. The effects of various parameters like molar ratio of substrates (isopropanol and acetic acid; 25 to 100 mM), concentration ofbiocatalyst (25–125 mg/mL), reaction time, reaction temperature, organic solvents,molecular sieves, and initial water activity werestudied for optimal ester synthesis. Under optimized conditions, 66.0mM of isopropyl acetate was produced when isopropanol and acetic acid were used at 100mM: 75mM in 9h at 55◦C in n-heptane under continuous shaking (160 rpm) using bound lipase(25mg). Addition of molecular sieves (3 °A ×1.5mm) resulted in a marked increase in ester synthesis (73.0mM). Ester synthesiswas enhanced by water activity associated with pre-equilibrated saturated salt solution of LiCl. The immobilized lipase retained more than 50% of its activity after the 6th cycle of reuse.

Self-cleaning, superhydrophobic cotton fabrics with excellent washing durability, solvent resistance and chemical stability prepared from an SU-8 derived surface coating

Superhydrophobic cotton fabrics with a very low contact angle hysteresis were prepared using a single-pot coating solution comprising SU-8 (a negative photoresist), a fluorinated alkyl silane and silica nanoparticles. The fabric was treated using a dip-coating technique and subsequently cured under UV light. The coated fabric showed excellent superhydrophobicity with a water contact angle as high as 163° and a sliding angle as low as 2°. The coating was durable enough to withstand 100 laundry cycles. It also had excellent stability against long immersion times in organic solvents, and acid and base solutions.