Enhancement of flux and solvent stability of Matrimid® thin‐film composite membranes for organic solvent nanofiltration

The development of high flux and solvent‐stable thin‐film composite (TFC) organic solvent nanofiltration (OSN) membranes was reported. A novel cross‐linked polyimide substrate, consisting of a thin skin layer with minimum solvent transport resistance and a sponge‐like sublayer structure that could withstand membrane compaction under high‐pressure was first fabricated. Then the solvent flux was significantly enhanced without compromising the solute rejection by the coupling effects of (1) the addition of triethylamine/camphorsulfonic acid into the monomer solution, and (2) the combined post‐treatments of glycerol/sodium dodecyl sulphate immersion and dimethyl sulfoxide (DMSO) filtration. Finally, the long‐term stability of the TFC membrane in aprotic solvents such as DMSO was improved by post‐crosslink thermal annealing. The novel TFC OSN membrane developed was found to have superior rejection to tetracycline (MW: 444 g/mol) but was very permeable to alcohols such as methanol (5.12 lm^?2h^?1bar^?1) and aprotic solvents such as dimethylformamide (3.92 lm^?2h^?1bar^?1) and DMSO (3.34 lm^?2h^?1bar^?1). © 2014 American Institute of Chemical Engineers AIChE J, 60: 3623–3633, 2014     

Effect of viscosity and volume on the specific conductivity of lithium salts in solvent mixtures

As part of a study on the optimization of the electrolyte for high energy lithium batteries, the conductivity, viscosity and density of LiAsF₆, LiBr, and LiClO₄ were measured in aprotic solvent mixtures. The conductivity of lithium bis(trifluoromethylsulfone)imide (LiTFSI) was also obtained in a large number of mixed aprotic solvents. The solvents were chosen to verify the effect of various parameters such as viscosity, permittivity, volume, acceptor number and donor number on the conductivity. These results were used to develop a simple model for excess conductivities based on the viscosity and volume of the pure solvents. Without adjustable parameters, this model predicts the correct sign of the excess conductivities in ≈90% of the cases and the magnitude of the conductivity of the ternary mixtures within an average of 15%. Deviations from the predictions are mostly observed with solvents of low permittivity and this supports the hypothesis that a different conduction mechanism is in operation at high concentration in these solvents, and the solvating power of these solvents plays an important role in this mechanism.     

Spiropyran, chromene and spirooxazine, mélange á trois: Molecular logic systems through selective and reversible deactivation of photochromism mediated by CO2 gas

We report a new expanded molecular logic system based upon combinations of spiropyrans, spirooxazines and chromenes, whereby the photochromism of some molecules can be selectively preserved while reversibly deactivating the photochromism of others. The non-photochromic molecules can be reversibly activated by CO₂ gas. It was found that the photochromic effect of spiropyrans, in general, and one spirooxazine (with a hydroxyl group on the naphtho-ring) could be reversibly deactivated by DBU, while a chromene and an unsubstituted spirooxazine remained photochromic in the system under the same conditions. The presence of protic solvent was necessary for the deactivation of some of these photochromic molecules and hence it was used as an additional sensitizer in the system. This afforded the expansion of stimuli for molecular logic operations and allowed combinations of the benign stimuli of UV, visible light, CO₂, and CO₂ depleted with protic and aprotic solvents. This effect provided the mechanism for molecular logic systems that do not suffer from the usual problems of dilution effects and hence become truly reversible. This is highly significant when designing molecular switches to perform logic operations.     

Solvent Effects on the Selectivity of Palladium-Catalyzed Suzuki-Miyaura Couplings

The use of polar solvents MeCN or dimethylformamide (DMF) was previously shown to induce a selectivity switch in the Pd/P^tBu₃-catalyzed Suzuki-Miyaura coupling of chloroaryl triflates. This phenomenon was attributed to the ability of polar solvents to stabilize anionic transition states for oxidative addition. However, we demonstrate that selectivity in this reaction does not trend with solvent dielectic constant. Unlike MeCN and DMF, water, alcohols, and several polar aprotic solvents such as MeNO₂, acetone, and propylene carbonate provide the same selectivity as nonpolar solvents. These results indicate that the role of solvent on the selectivity of Suzuki-Miyaura couplings may be more complex than previously envisioned. Furthermore, this observation has the potential for synthetic value as it greatly broadens the scope of solvents that can be used for chloride-selective cross coupling of chloroaryl triflates.     

A Kinetics and Mechanism Investigation of the Nucleophilic Substitution Reaction of <Emphasis Type="Italic">α-</Emphasis>Chlorododecyl Carboxylate with Trimethylamine

A nucleophilic substitution reaction was developed to synthesize the zwitterionic surfactant using a renewable natural fatty acid rather than a petroleum derivative as the raw material. The kinetics and mechanism of the nucleophilic substitution reaction of trimethylamine α-chlorododecyl carboxylate with trimethylamine were investigated in protic and dipolar aprotic solvents including water, ethanol and N, N-dimethyl formamide. The rate equations were derived using initial rates and the activation parameters in different solvents were determined empirically and compared with each other to obtain important information about the reaction mechanism. The overall second-order reaction number and the negative activation entropy supported a bimolecular nucleophilic substitution (S_N2) mechanism, combined with the pseudo-first-order kinetics for each reactant. The experimental results also showed that the reaction reactivity diminishes with the decrease in polarity of protic solvents. The typical dipolar aprotic solvent dimethyl formamide distinctively promoted the reaction in. This fact was successfully explained by the solvation rule for S_N2 reactions.     

Effect of protic solvents on the physical properties of the ambient pressure dried hydrophobic silica aerogels using sodium silicate precursor

Considering the importance of the highly porous, low density, transparent and nanostructured hydrophobic silica aerogels in the scientific and industrial applications, the experiments have been carried out to prepare the low density silica aerogels using the 1.12 specific gravity water glass (sodium silicate, Na₂SiO₃) precursor, ammonium hydroxide (NH₄OH) catalyst, trimethylchlorosilane (TMCS) silylating agent, various first exchanging protic solvents and hexane as a second exchanging aprotic solvent. The first exchanging solvents used were: methanol, ethanol, propanol, isopropanol, butanol, isobutanol and hexanol. The molar ratio of the Na₂SiO₃:H₂O:NH₄OH:TMCS was kept constant at 1:56:0.02:0.4 respectively. The ambient pressure dried method was used for the preparation of hydrophobic silica aerogels. The effect of the exchanging protic solvents on the physical properties of the aerogels such as density, % of volume shrinkage, % of porosity, % of optical transmission, thermal conductivity, thermal stability and contact angle of the aerogels with water, were studied. FTIR studies were carried out to confirm the silylation of the aerogel samples. It was found that the exchanging protic solvents have profound effect on the physical and hydrophobic properties of the aerogels. Low density (0.07 g/cm³), high porosity (96.6 %), low thermal conductivity (0.091 W/mK), high contact angle (166°) silica aerogels could be prepared by using the isopropanol first exchanging solvent followed by the hexane as the second exchanging solvent along with the TMCS silylating agent with sodium silicate precursor.     

Adsorption of poly(dimethyl siloxanes) from solution on silica: 1

The adsorption of a broad range of poly(dimethyl siloxanes) on silica, treated and untreated, has been studied. Three solvents, n-hexane, CCl₄, and benzene were employed. Adsorption was molecular weight dependent and more polymer adsorbed from n-C₆H₁₄ than from CCl₄. Only negative adsorption from C₆H₆ solution was observed. The results are rationalized on the basis of the polymer—solvent interaction values (χ), the solvent—adsorbent and the solute—adsorbent adsorption energies. It is concluded that the loss in configurational entropy on adsorption of the macromolecules is a major factor in determining the adsorption isotherms.     

The solubility of sulfur dioxide and hydrogen sulfide in associating solvents

The solubilities of SO₂ are reported in the solvents N, N-dimethyl acetamide (DMA), N, N-dimethyl formamide (DMF), ethyl acetate, acetonitrile, chlorobenzene, methanol, (1,2-ethanediol) ethylene glycol and acetone for atmospheric pressure and for temperatures ranging from 268 K to 333 K (-5°C to 60°C). Solubilities of H₂S are also reported for the first five of the above-mentioned solvents and for hexane for similar conditions. These gases and solvents exhibit extreme molecular interactions which are reflected in unusual solubility behavior. This paper is a continuing attempt in providing data and analyses for improving the understanding of gas solubilities in complex gas-solvent systems. Solubilities expressed as hydrogen-bonding factors have been found useful in systematically relating gas solubilities in one associating or reacting solvent to another chemically similar solvent. Thus, with a limited amount of data for gas solubilities, it is often possible to predict solubilities even in highly associated or reacting gas-solvent solutions.     

Ozonolysis of Canola Oil: A Study of Product Yields and Ozonolysis Kinetics in Different Solvent Systems

The use of ozonolysis has been proposed as a step in the production of vegetable-oil-based polyols as replacements for the equivalent petrochemicals. As part of an evaluation of the commercial viability of ozonolysis, the intermediates and products formed from the ozonolysis of canola oil using different protic and aprotic solvents and solvent mixtures were systematically studied by GC-FID and size-exclusion chromatography with refractive index detection (SEC-RI). It was found that the use of an aprotic solvent (ethyl acetate) leads to the formation of oligomeric ozonolysis products whereas alcohols and/or mixtures of ethyl acetate with alcohols for the ozonolysis of canola oil do not form high molecular weight compounds. In addition, when ethyl acetate is used as the solvent, the formation of carboxylic acids is observed in the early stages of ozonolysis whereas the use of alcohols significantly reduces acid formation. As expected, extending the ozonolysis time led to extensive carboxylic acid formation, especially using ethyl acetate as a solvent. It was found that the optimum time for the complete ozonolysis of canola oil was largely independent of the solvent used for ozonolysis. However, the yield of ozonolysis products differs considerably depending on the solvents employed. Overall, a clear correlation between the ozonolysis time, product yields and the reaction exothermicity was observed.     

Polyoxometalate catalyzed ozonation of chemical pulps in organic solvent media

Polyoxometalate (POM) catalyzed ozonation of chemical pulps in organic solvent media was found to be particularly effective and selective environmentally benign bleaching approach providing a way for substantial increase in pulp brightness, viscosity and degree of delignification in comparison with other ozone-based bleaching techniques. A series of tested low-boiling polar aprotic and protic organic solvents showed a well-defined capacity for ozonation improvement in the presence of Keggin-type heteropolyanion [PMo₇V₅O₄₀]⁸⁻ (HPA-5). Even moderate solvent proportion of 6% (w/w) in the reaction solution caused additional gain in brightness up to 3.4% ISO with simultaneous increase in pulp viscosity up to 8.8% and lignin removal up to 18.9% after HPA-5 catalyzed ozonation (0.8% O₃; 0.5 mM HPA), as compared with the control solvent-free process. An aqueous acetone solution was found to be the preferred reaction medium in terms of pulp brightening and delignification. Under optimized conditions, the POM-catalyzed ozonation of eucalypt kraft pulp in acetone/water solution showed remarkable brightness improvement by 15.1% ISO with additional lignin removal by 39.4% and increase in intrinsic viscosity by 3% in comparison with pulp bleached in water media.     

Synthesis of transparent poly(vinylidene fluoride) (PVdF)/zirconium oxide hybrids without crystallization of PVdF chains

Transparent and homogeneous organic-inorganic hybrids with poly(vinylidene fluoride) (PVdF) could be prepared by addition of zirconium oxide nanocrystals (ZrO₂-NCs) in a polar aprotic solvent and the subsequent solvent evaporation. The polar aprotic solvents such as DMF, DMAc and DMSO would form hydrogen bonds with Zr-OH groups of the ZrO₂-NC and play a role as compatibilizers between the PVdF and ZrO₂-NCs. The interpenetration between PVdF and ZrO₂-NCs resulted in the nanometer dispersion of PVdF chains in a ZrO₂-NC matrix. High dosage of the ZrO₂-NCs as physical inhibitors between PVdF polymer chains sufficiently prevented the PVdF chain mobility in the internal of hybrids. The transparency of the PVdF/ZrO₂-NC hybrids was dramatically improved by controlling the content of ZrO₂-NCs. Novel multifunctional hybrids with high transparency, high refractive index and good mechanical property were obtained by hybridization of PVdF and ZrO₂-NCs.     

Lithium?Oxygen Electrochemistry in Non-Aqueous Solutions

Pairing lithium and oxygen in aprotic solvents can theoretically lead to one of the most promising electrochemical cells available. If successful, this system could compete with technologies such as the internal combustion engine and provide an energy density that can accommodate electric vehicle demands. However, there are many problems that have inhibited this technology from becoming realistic. One of the main reasons is capacity fading after only a few cycles, which is caused by the instability of electrolyte solutions in the presence of reduced oxygen species like O₂^.− and O₂²⁻. In recent years, using various analytical tools, researchers have been able to isolate the breakdown products arising from the reactions occurring between the aprotic solvent and the reduced oxygen species. Nevertheless, no solvents have yet been found that are fully stable throughout the reduction and oxidation processes. However, an understanding of these decomposition mechanisms can help us in designing new systems that are more stable toward the aggressive conditions taking place in Li O₂ cell operation. This review will include analytical studies on the most widely used solvents in current Li O₂ research.     

Synthesis of 2-mercaptobenzimidazole from the reaction of o-phenylene diamine and carbon disulfide in the presence of potassium hydroxide

The reaction of o-phenylene diamine and carbon disulfide to synthesize 2-mercaptobenzimidazole (MBI) enhanced by potassium hydroxide was carried out in a homogeneous solution. No catalysts are required in the reaction. In addition to the reaction of carbon disulfide and hydrogen sulfide to produce S²⁻ and CS₃²⁻, potassium hydroxide is also acted as the enhancer to promote the reaction of synthesizing MBI. A mixture of organic solvent (protic or aprotic solvent) and water is used as the reaction solution in order to obtain a homogeneous phase. The effects of the reaction conditions, including the amount of o-phenylene diamine, amount of carbon disulfide, organic solvents, volume ratio of organic solvent to water, and temperature, on the conversion of o-phenylene diamine were investigated in detail. An appropriate amount of KOH is recommended to produce a high yield of MBI and a high reaction rate in using protic solvent/water as the mixed solution. Nevertheless, the conversion is increased with the increase in the amount of KOH using aprotic solvent. This behavior is different from that of the KOH effect on the conversion of o-phenylene diamine using protic solvent/water as the mixed solution.     

Synthesis and characterization of poly(amide imides) containing benzimidazole-rings

New poly(amide imides) were prepared from benzimidazole-ring containing diamine via one-pot synthetic method. The diamine monomer, 6,4′-diamino-2-phenylbenzimidazole, was prepared from 4-nitrobenzoyl chloride and 4-nitro-1,2-phenylenediamine with 3 steps. It was found that the degree of imidization of the poly(amide imides) containing benzimidazole-ring can be controlled by monomer composition and solution imidization conditions. All partially imidized poly(amide imides) were soluble in polar aprotic solvent, but became insoluble in any organic solvents after thermal curing. The thermal stability of the poly(amide imides) increased as the polymers contain more benzimidazole units. Received: 6 March 1997/Accepted 2 April 1997     

Solvent effect on the kinetics of the electrooxidation of phenothiazine

One-electron oxidation of phenothiazine to the corresponding radical cation was used as a model system to study the solvent effect on the heterogeneous charge-transfer kinetics. The standard rate constant of the studied electrode reaction was found to depend considerably on the nature of the solvent. The experimental kinetic data has been interpreted in terms of the dielectric dynamic properties of the solvent. The linear relationships between the standard rate constant and the reciprocal of the longitudinal dielectric relaxation time of a given solvent have been found in the aprotic case as well as for hydrogen-bonded solvents. The difference between both groups of solvents may be explained by the different dielectric relaxation behaviour or by the difference in the reaction site in respect to the electrode surface.     

Design and stabilization of block copolymer micelles via phenol-pyridine hydrogen-bonding interactions

A new approach for the preparation of block copolymer micelles in non-selective solvent is introduced. Phenol-pyridine hydrogen-bonding interactions are used for the first time to prepare core-shell micelles in non-selective solvents using block copolymers and bifunctional low-molecular-weight hydrogen-bonding crosslinkers. Poly(styrene-b-4-vinylphenol)/Bis-pyridyl ethane and poly(styrene-b-4-vinylpyridine)/Bisphenol A were investigated as micelle formation due to phenol-pyridine hydrogen bond crosslinking. The influence of several factors such as temperature, concentration, solvent and pH in micellization-demicellization process was analyzed by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic light scattering (DLS) and atomic force microscopy (AFM). This method opens new possibilities to the generation of block copolymer micelles in non-selective solvents.     

Synthesis,Characterization, and Electrical Properties of New Crosslinked Conjugated Polymer Based on Acetyl Acetone Moiety

A new crosslinked conjugated polymer has been prepared by condensation of acetyl acetone with terephthalaldehyde using hydrogen chlorides as a catalyst and ethanol as a solvent. The resulting polymer was investigated by spectroscopic methods (IR,¹H-NMR). The inherent viscosity was found to be about 0.92 dl/g. The crosslinked conjugated polymer is semicrystalline and partially soluble in most common organic solvents but freely soluble in the aprotic solvent. The synthesized polymer was evaluated by TGA analyses and has been found to be thermally stable. The morphology of the dry polymer was examined by scanning electron microscope, and the electrical conductivity was found to be in the range of 10^?6 Ω^?1 m^?1 at room temperature and above up to 44°C.     

Struktur des basischen Zink-O,O′-2-ethylhexyldithiophosphats in unpolar,aprotischen Lösungsmitteln

Structure of Basic Zinc-O,O′-2-ethylhexyldithiophosphates in Apolar Aprotic Solvents A sample of technically used Zinc-O,O′-2-ethylhexyldithiophosphate enriched by basic Zinc-O,O′-2-ethylhexyldithiophosphates (i-C₈-ZnDTP) was investigated in aprotic apolar solvents by integral and structure specific analytical methods. The results let us suppose that the structure of basic i-C₈-ZnDTP in apolar aprotic solvents can be described by an Zn₃-complex of type ZnO(ZnDTP)₂.     

Thermostable variants constructed via the structure-guided consensus method also show increased stability in salts solutions and homogeneous aqueous-organic media

Enzyme instability is a major factor preventing widespread adoption of enzymes for catalysis. Stability at high temperatures and in the presence of high salt concentrations and organic solvents would allow enzymes to be employed for transformations of compounds not readily soluble in low temperature or in purely aqueous systems. Furthermore, many redox enzymes require costly cofactors for function and consequently a robust cofactor regeneration system. In this work, we demonstrate how thermostable variants developed via an amino acid sequence-based consensus method also showed improved stability in solutions with high concentrations of kosmotropic and chaotropic salts and water-miscible organic solvents. This is invaluable to protein engineers since deactivation in salt solutions and organic solvents is not well understood, rendering a priori design of enzyme stability in these media difficult. Variants of glucose 1-dehydrogenase (GDH) were studied in solutions of different salts along the Hofmeister series and in the presence of varying amounts of miscible organic solvent. Only the most stable variants showed little deactivation dependence on salt-type and salt concentration. Kinetic stability, expressed by the deactivation rate constant k(d,obs), did not always correlate with thermodynamic stability of variants, as measured by melting temperature T(m). However, a strong correlation (R(2) > 0.95) between temperature stability and organic solvent stability was found when plotting T(50)(60) versus C(50)(60) values. All GDH variants retained stability in homogeneous aqueous-organic solvents with >80% v/v of organic solvent.