In situ characterization of RF field-induced reactions by Raman spectroscopy - II. Effects of additives on urethane formation kinetics and mechanisms

The effects of RF fields on the reaction kinetics of urethane formation in the presence of a catalyst, ionic compounds or polar solvents were studied using in situ Raman spectroscopy. Kinetics simulations based on a simple second-order reaction model were used to verify the reaction mechanism. A maximum reaction rate of about 10% per second for urethane formation with 100 ppm NaCl, 25 ppm dibutylin diacetate, and 3.75 mol% DMSO was observed under an RF field of 6.3 kV/cm. The same reaction took more than 20 min to reach 60% conversion without the application of an RF field. However, the results of this work indicate that an intense RF field does not have a direct influence on the curing mechanism and kinetic parameters, although it has a very strong heating effect on the systems with ionic compounds and on the dielectric breakdown in the polar solvent vapor phase.     

Phase transfer catalysis

Summary Some basic types of phase transfer catalysts (PTC) were tested using the alkylation of phenol with butyl bromide as an example. Their activity decreases in the series ammonium salts — polyethylene-glycols — crown ethers. The reaction course is favourably affected by the polar solvent (dichloroethane), or by the nonpolar solvent (toluene) in the case of polyethyleneglycol. Immobilized catalytically active groups on the crosslinked polymer are always less active. The reaction rate in KOH is higher than in NaOH. The distribution of reaction components between the particular phases was investigated in detail, and conclusions regarding the reaction mechanism and kinetics were drawn from the distribution of concentrations.     

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.     

Enantioselective hydrogenation of (E)-α-phenylcinnamic acid with cinchonidine-modified Pd/TiO2: influence of solvents and additives

Both the enantioselectivity and activity of the hydrogenation of (E)-α-phenylcinnamic acid with cinchonidine-modified Pd catalysts are strongly solvent dependent; polar solvents with higher solubility for the substrate are preferable. The simultaneous increases in the enantioselectivity and activity, also induced by the addition of either a small amount of water to aprotic solvents or an amine such as benzylamine, indicate that preferential acceleration of the selective reaction has occurred, thus strongly suggesting the importance of the product desorption step on the modified sites. This revised version was published online in June 2006 with corrections to the Cover Date.     

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.     

Poly(ethylene glycol)‐containing cationic hydrogels with lipophilic character

Not much effort has been focused towards the development of hydrogels that swell in nonpolar solvents. We have synthesized a new set of polyelectrolyte hydrogels and demonstrated their ability to absorb a less‐polar or nonpolar organic solvent, as well as their ability to resist gel‐collapse in a predominantly nonpolar medium. The hydrogels were prepared by free radical polymerization of different molar ratios of poly(ethylene glycol) methyl ether acrylate and (3‐(methacryloylamino)propyl)‐trimethyl ammonium chloride as comonomers in an aqueous medium. Their swelling behavior in organic solvents was studied by varying the dielectric constant of the swelling medium including mixed‐solvent systems. Besides a high degree of swelling (up to 200 times) in polar solvents, some of the hydrogels also exhibited moderate swelling (up to 15 times) in less‐polar organic solvents. Hydrogels samples with high cationic content showed drastic change in swelling extent in some of the mixed‐solvent systems. It was also interesting to note that the retention of significant swelling in dimethyl sulphoxide–toluene mixture with even 90% toluene content for some compositions. These polyelectrolyte hydrogels with improved lipophilicity opens up greater opportunities for the development of even superior soft materials through proper structural optimizations that would successfully function for a wider range of solvents. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39873.     

Dielectric properties of an epoxy resin and its composite II. Solvent effects on dipole relaxation

Dipole relaxation dielectric loss behavior of a fiberglass-epoxy composite has been studied following submersion in polar and nonpolar organic solvents as well as in acidic and basic aqueous solutions. Certain adsorbed organic solvents, such as 1,2-dichloroethane, had little influence on the epoxy relaxation behavior. Other solvents, including chloroform, increased the composite relaxation intensity and shifted the temperature-frequency region over which the relaxation occurred. Both the amount of solvent uptake and the degree of interaction of solvent molecules with epoxy polar functional groups appear to control the amount of relaxation behavior perturbation. Arrhenius activation energies for relaxation were lowered by solvent uptake from the dry composite value of 18 kcal/M to between 6 and 16 kcal/M, depending on the solvent adsorbed. Submersion in methanol and chloroform sharply increased the direct current conductivity of the composite. Two molar acidic and basic solutions had little influence on composite dipole relaxation behavior other than the well known behavior associated with moisture uptake.     

Effect of filler geometry on the diffusion and transport behavior of aromatic solvents and commercial oil through nitrile rubber nanocomposites

The diffusion and transport behavior of nitrile rubber nanocomposites was studied with respect to different types of filler and also different types of solvents. The nitrile rubber nanocomposites showed considerable variations in the molecular transport owing to the tortuosity of path, decreased segmental mobility, and difference in particle geometry. As the matrix under consideration is polar, the behavior of the filled systems in aniline was also studied with a view to understand the polar–polar interaction between the filled matrix and the solvent. The oil repellency as a result of filler addition in the matrix was investigated by studying oil uptake of the nanocomposites. In all these investigations, it has been observed that the filler geometry played an important role in controlling the molecular transport through the polymer matrix. The layered silicate‐filled system showed better solvent resistance and hence minimum solvent uptake in polar and nonpolar solvents and better oil repellency followed by titanium dioxide and calcium phosphate filled systems. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Sulfonated polyisobutylene telechelic ionomers. XIII. Viscosity behavior in nonpolar solvents and nonpolar–polar solvent mixtures

The effect of molecular variables upon the dilute solution viscosity of sulfonated polyisobutylene telechelic ionomers has been studied in both nonpolar solvents and nonpolar–polar solvent mixtures. In nonpolar solvents, association of the terminal salt groups results in an increase in viscosity and gelation at very low concentrations. The concentration at which gelation occurs was found to be dependent upon molecular variables such as architecture, molecular weight, neutralizing cation, extent of neutralization, and the type of solvent. Addition of a small amount of a more polar cosolvent tends to break up ionic associations between polymer chains and thus reduces viscosity. Finally, such solutions with a small amount of polar cosolvent may display dramatic increases in viscosity with increasing temperature due to a dynamic equilibrium between the ionic groups on the polymer chain, the nonpolar solvent, and the polar cosolvent. The results of this work suggest that these ionomers may potentially be useful as viscosity modifiers or “thermal thickeners” in some applications.     

The hydrolysis of phosphatidylcholine by an immobilized lipase: Optimization of hydrolysis in organic solvents

The ability of a commercial immobilized lipase preparation (Lipozyme) to hydrolyze the fatty acyl ester bonds of soybean phosphatidylcholine in organic media was investigated. Response surface methodology, based on a Modified Central Composite design, was employed to examine the effects on hydrolysis of solvent polarity, water, pH, duration and temperature of incubation, and the amounts of substrate and catalyst. A second-order regression model was developed, which allows evaluation of the effects of these parameters, alone or in combination. Hydrolysis increased in a relatively straightforward manner in response to increases in incubation time and the amount of catalyst and was approximately constant over the range of substrate amounts studied. Solvent polarity had a profound effect on the degree of hydrolysis, and the qualitative and quantitative degrees of this effect were dependent upon the values of the other parameters studied. Conditions were identified where enzyme activity was strong in either nonpolar or polar solvents, with activity increasing as the polarity of the medium increased. Enzyme activity was minimum at about 37°C, increasing below and above this temperature. Activity was not affected by the presence of acid or base in the reactions. Increasing amounts of water stimulated enzyme activity in solvents more polar than hexane, while in less polar solvents water inhibited activity.     

Synthesis of novel amphiphilic pH‐sensitive polyurethane networks through W/O soap‐free emulsion polymerization process. II. Mechanical property and biphasic swelling behaviors

Amphiphilic urethane acrylate anionomer (UAA) chains exhibited very different solution properties in various solvents, such as water, dioxane, and dimethyl sulfoxide (DMSO). UAA chains showed a polyelectrolyte effect in a highly polar solvent, DMSO, but gave constant viscosity at various concentrations in aqueous solution, because of the microstructural difference of the UAA chain formed in solvents. In polar solvents (water and DMSO), the swelling of UAA networks prepared with water and dioxane strongly depended on the properties of the hydrophilic domains. In low and nonpolar solvents (dioxane and methylene chloride), the swelling of UAA networks was only dependent on the property of the hydrophobic segments. In the polar solvent medium, UAAG networks prepared with water exhibited greater swelling than UADG networks prepared with dioxane. Concerning swelling in a nonpolar solvent, however, UADG networks showed greater swelling than UAAG networks. This is because of the microstructural difference between these networks, which was confirmed by the mechanical property measurement. UAAG networks, having highly microphase‐separated structures, had higher modulus and transition temperatures than the UADG networks, because of the microstructural difference between UADG and UAAG networks. Both the UAAG and UADG networks take up two immiscible solvents simultaneously within their hydrophobic and hydrophilic domains. Equilibrium swelling ratio of these networks in two immiscible solvents strongly depends on their hydrophilic/hydrophobic balance that is controlled by the type of solvent used in the network synthesis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 621–630, 2001     

Thermodynamic interactions of branched polyethylene in polar and nonpolar systems

The thermodynamic properties of polymer solutions are frequently described in terms of the Flory-Huggins equation. This equation includes a parameter χ, which depends upon the intermolecular forces acting between the molecules in a solution. The experimental determination of χ was performed by an improved microtechnique and extended to a wide range of polar and nonpolar diluents of polyethylene. Careful correlations are prescribed for calculating χ from pure-component properties; they are based on an extension of the Hildebrand-Scatchard theory of solutions and on the theory of intermolecular forces. Polar (τ) and nonpolar (δ) solubility parameters are presented for a variety of solvents. For polyethylene—nonpolar solvent systems we have emphasized the factor deciding the sign of heat of mixing, while for polyethylene-polar solvent systems we have determined the contribution of dipole-induced dipole interactions ψ (δτ) in interchange-energy density B and, hence, χ.     

Fast swelling behaviors of thermosensitive poly(N‐isopropylacrylamide‐co‐methacryloxyethyltrimethyl ammonium chloride)/Na2WO4 cationic composite hydrogels

A facile method was explored to synthesize thermosensitive poly[N‐isopropylacrylamide (NIPAM)‐co‐methacryloxyethyltrimethyl ammonium chloride (DMC)]/Na₂WO₄ cationic hydrogels via copolymerization of NIPAM and DMC in the presence of Na₂WO₄. Na₂WO₄ acted as both a physical crosslinking agent and a porogen precursor. The hydrogels were characterized by Fourier transform infrared spectroscopy, energy dispersive X‐ray, thermogravimetry, environmental scanning electron microscopy, and transmission electron microscopy. Effects of various salt solutions, pH solutions on swelling were investigated. Thermosensitivity of the hydrogels were also investigated in various polar solvents at different temperatures. The resultant hydrogel showed a fast swelling rate and good salt tolerance. The hydrogels reached the swelling equilibrium within 10 min. Moreover, the swelling ratio of the hydrogels increased with the increase of the polarity of the solvent. In the water, the swelling ratio decreased with the increasing of temperature, but remained at a high level even at 80 °C since the pore structure weaken the lower critical solution temperature effect of PNIPAM. The swelling ratio increased instead in low polar solvent, while it became negligible in nonpolar solvent with the increasing of temperature. The whole swelling kinetics was fit for Schott's pseudo‐second order model. The hydrogels have a great potential as catalysts and smart materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46375.     

有机胺非水溶液吸收CO2的动力学研究进展

有机胺水溶液吸收法是CO₂捕集最常用且成熟的方法之一,但是再生能耗高和吸收剂严重降解等关键问题阻碍了其大规模推广和应用。采用有机溶剂代替强极性水溶剂构建的非水吸收剂体系,在降低能耗方面具有巨大潜力,在近年来受到格外关注。非水吸收剂的CO₂吸收动力学研究有助于了解吸收过程的反应机理以及不同有机胺和溶剂类型对反应动力学的影响。本文从有机胺在非水溶剂中的反应机理出发,介绍了CO₂吸收动力学研究的典型实验方法和原理,系统评述了采用不同结构的有机胺在不同溶剂体系中吸收CO₂的动力学研究进展,深入分析了溶剂特性与胺的反应级数和反应动力学常数之间的关联性,并指出了普遍的规律性特征即有机伯胺和仲胺的反应级数随溶剂极性的降低而增大,反应速率常数随着溶剂的溶解度参数增大而呈现近似线性变化。在分析目前动力学研究中存在的问题基础上,对今后非水体系动力学的研究方向进行了展望。     

Solvent effects in the kinetics of the enantioselective hydrogenation of ethyl pyruvate

The influence of solvent on the kinetics of enantioselective hydrogenation of ethyl pyruvate by Pt/Al₂O₃/dihydrocinchonidine is reported. In a non‐polar solvent, toluene, the reaction is approximately zero order in substrate at constant hydrogen pressure, while under the same conditions and at the same substrate concentration, in the polar solvents ethanol and propylene carbonate the reaction shows a first‐order substrate concentration dependence. Fits to a Michaelis–Menten rate expression show that these differences are the expression of the relative magnitudes of the adsorption term in the rate expression, which in turn reflects the influence of the solvent on the adsorption–desorption processes which take place at the catalyst surface. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of (all‐rac)‐α‐Tocopherol Using Fluorinated NH‐Acidic Catalysts

The synthesis of (all‐rac)‐α‐tocopherol starting from trimethylhydroquinone and isophytol using fluorinated NH‐acidic catalysts is described. Scope and limitations of this type of catalysts are discussed. Advantages of this new procedure are high yield and selectivity, no waste problem and mild reaction conditions. Best results in the synthesis of (all‐rac)‐α‐tocopherol (94% yield) using NH‐acidic compounds are obtained in polar solvents. The used catalyst could be recovered.     

A highly regioselective synthesis of δ-lactones from meadowfoam fatty acids

Meadowfoam fatty acids, when treated with mineral acid catalysts in the presence of polar nonparticipating solvents, undergo a facile ring closure to form δ-lactones. Perchloric and sulfuric acids catalyze the cyclization at concentrations of 0.6–13 mole equivalents, both neat and in the presence of solvent. Under constant acid concentrations, methylene chloride was found to increase the rate of reaction, the regioselectivity for the formation of δ-lactone, and the overall yield. In the absence of solvent, increased acid concentration improved the yield of lactone but reduced regioselectivity for the δ-isomer. Solvent polarity plays a significant role in the regioselectivity of the cyclization for δ-lactone, with solvents of higher dielectric strength providing larger δ/γ ratios (38:1) and higher yields up to 92%.     

The effect of relative concentrations on the efficiency of separation of polar and nonpolar lipids by alumina column chromatography

Columns were packed with aluminas from various sources and of low and high adsorptive power. Polar and nonpolar lipids were eluted from them with strong and weak solvents, and the fractions were tested for phosphorus, nitrogen, sterols, and triglycerides. The conditions used by the 1956 Technical Committee of the N.S.P.A. for the chromatography of linseed oil gave the most complete separation of polar from nonpolar lipids when the former were present in low concentration. When the lipid phosphorus load approached 0.4 mg./gm. alumina however, none of the alumina systems tried was satisfactory although silicic acid columns resolved the mixtures completely. Gamma alumina had greater resolving power thanalpha alumina monohydrate. Brockmann Grade I alumina with a strong solvent system gave better speration than weaker aluminas with weaker solvent systems. Presented at the fall meeting, American Oil Chemists' Society, Los Angeles, Calif., September 28–30, 1959. Contribution No. 44 from the Genetics and Plant Breeding Research Institute, Research Branch, Canada Department of Agriculture, Ottawa, Ontario.     

Enzymatic phosphatidylcholine hydrolysis in organic solvents: An examination of selected commercially available lipases

Eight commercial lipase preparations were examined for the ability to hydrolyze phosphatidylcholine (PC) in hexane solutions. Only the enzymes fromHumicola lanuginosa, Rhizopus delemar andCandida rugosa displayed appreciable activity. Solvent polarity was the largest single factor affecting activity. TheH. lanuginosa sample was most active in polar solvents. TheR. delemar preparation was most active in polar (2-hexamone) and nonpolar (decane) solvents and least active in solvents of intermediate polarity (hexane). The solvent dependence of the activity of theC. rugosa enzyme varied with the ratio of substrate to enzyme. Different degrees of activity were retained by the three enzymes after passive immobilization on Celite, controlled-pore glass, polypropylene and Amberlite XAD-7 resins. No single resin yielded the best retained activity for all three preparations. When examined in 2-octanone, hexane and isooctane, the Celite-immobilizedR. delemar andH. lanuginosa enzymes exhibited highest activity in 2-octanone, while immobilizedC. rugosa was most active in isooctane. The water content at which maximum activity was observed was relatively independent of solvent polarity and the amount of catalyst but was proportional to the amount of PC in the reaction. The retention of activity by immobilizedRhizomucor miehei lipase (Lipozyme) during multiple hydrolytic cycles required a reduction in the water content of the system below that yielding optimal activity in a single cycle.     

Polymer‐supported palladium(II) complexes and their catalytic study

Chloromethylated poly(styrene–divinylbenzene) copolymers with 8 and 14% crosslinking was functionalized to a Schiff‐base‐bearing polymer by the sequential oxidation of the chloromethyl group to an aldehydic group and subsequent condensation with a base. The anchoring of the metal ion to the liganded polymer beads was carried out by its reaction with an ethanolic solution of palladium(II) chloride. The physicochemical properties of the supported catalyst, including surface area, bulk density, and the swelling of the polymer in polar and nonpolar solvents, were studied. The catalysts were characterized by various techniques, including elemental analysis, DTA–thermogravimetric analysis, Fourier transform infrared spectroscopy, and diffuse reflectance spectroscopy. The surface morphology of the catalyst was studied by scanning electron microscopy. The catalytic hydrogenation of cis‐cyclooctene was investigated with the immobilized catalysts. The effects of various reaction parameters, including catalyst concentration, temperature, and hydrogen pressure on the reduction of olefin, were studied. The rate of the reaction was determined from hydrogen uptake measurements. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 370–378, 2003