Showing papers on "Solvent published in 1979"

Solvent Effects in Organic Chemistry

Abstract: Intermolecular forceds, interactions between solute and solvent. Solvation. Classification of solvents. Chemical action of solvents: effects on equilibria and reactions. Effects on absorption spectra of organic compounds. Empirical parameters of solvent polarity. Toxicity, table of threshold values, tl and mak. -- ICCROM

Solution properties of poly(N‐isopropylacrylamide)

Abstract: The results obtained by light scattering and viscosity measurements on unfractionated samples of poly(N-isopropylacrylamide) dissolved in methanol and in water seem to show that the chain molecules assume different conformations in the two solvents. In methanol solutions at 25°C, poly(N-isopropylacrylamide) (poly[1-(N-isopropylaminocarbonyl)ethylene]) molecules apparently behave as normal flexible chains, whereas in aqueous solutions at the same temperature the interactions between polymer molecules and the solvent seem to produce chain uncoiling toward more extended structures which become unstable at higher temperatures.

Ethyl acetate as a substitute for diethyl ether in the formalin-ether sedimentation technique.

Abstract: Ethyl acetate appears to be a satisfactory subsitute solvent for diethyl ether in the Formalin-ether sedimentation technique. In comparative studies, concentration of organisms with ethyl acetate was equal to or greater than that with diethyl ether. No distortion or alteration of morphology was observed with eigher solvent, and preparations were comparable in appearance and ease of examination. In addition, ethyl acetate is less flammable and less hazardous to use than diethyl ether.

A survey of ligand effects upon the reaction entropies of some transition metal redox couples

Abstract: The reaction entropies lSo,, of a number of transition metal redox couples of the form M ( I I I ) / ( 11) in aqueous solution have bcen determined using nonisothermal electrochemical cells in order to explore the effect of varying the ligand structure upon the nature of the ion-solvent interactions. Examination of six aquo couples of the form M ( O H Z ) , , ~ + ' ~ + with varying metal M yielded ASo,, values in the range 36-49 eu. In order to scrutinize the effect of replacing aquo with ammine and simple anionic ligands, R u ( l I I ) / ( I I ) couples were employed since the relativc substitution inertness of both oxidation states allowed AS',, to be determined using cyclic voltammetry. The stepwise replacement of aquo by ammine ligands results in substantial reductions in ASo,, which are attributed to the smaller extent of ligand-solvent hydrogen bonding for ammine compared with aquo ligands. Substitution of both aquo and ammine by anionic ligands also resulis in substantial reductions in ASo,,. A number of M ( I I I ) / ( I I ) couples containing chelating ligands were also examined. Sizable differcnces in ASo,, were found between Co(lll)/(ll) couples and the corresponding R u ( l l l ) / ( l l ) and Fe(lll)/(ll) couples. Suggested explanations are differences in ligand conformation and electron delocalization effects. The possible contribution of outer-sphere solvent structuring effects to the large reorganization energies observed for electron exchange of aquo complexes is noted. The validity of the assumptions required for the estimation of ASo,, from nonisothermal cell measurements is discussed.

Reactions of organic free radicals at colloidal silver in aqueous solution. Electron pool effect and water decomposition

Abstract: Organic free radicals of high negative redox potential such as ..cap alpha..-alcohol radicals were found to transfer electrons to colloidal silver particles stabilized by sodium dodecyl sulfate in aqueous solution. The colloidal particles thus became a pool of stored electrons that could reduce water to form hydrogen or react with suitable acceptors in solution. The organic radicals were produced by irradiation, using suitable scavengers for the primary radicals from the radiolysis of the aqueous solvent. The solutions initially contained silver ions at 1 x 10/sup -4/ - 2 x 10/sup -3/ M. At doses below 10/sup 5/ rd, the silver ions were completely reduced to form the colloidal catalyst. In this dose range, the corresponding hydrogen yield amounted to 1 molecule per 100 eV. It increased steeply at higher doses up to 3 molecules per 100 eV. The H/sub 2/ yield decreased with increasing dose rate and with increasing pH in alkaline solutions. It was highest at a concentration of sodium dodecyl sulfate of 1 x 10/sup -3/ M, i.e., far below the critical micelle concentration of this surfactant. Changes in the absorption spectrum of the colloid are attributed to changes in the size of the silver particles upon chargingmore » up with electrons. The competition of radical-colloid reactions with radical-radical deactivation in the bulk of solution or at the surface of the colloidal particles is also discussed. 11 figures.« less

The origin of residual internal stress in solvent‐cast thermoplastic coatings

Abstract: Experiments on polystyrene and poly(isobutyl methacrylate) coatings cast from toluene have shown that residual internal stress is independent of dried coating thickness and initial solution concentration. A theory is presented that predicts the magnitude of the stress and shows that it has no dependence on thickness or initial solution concentration. Internal strain is calculated from the volume of solvent lost after the coating has solidified. This solidification point is identified with the solvent concentration that is sufficient to depress the glass transition of the polymer to the prevailing experimental temperature. A one-to-one correlation is confirmed between the volume of solvent lost from solution during drying and the volume change of the polymer film.

Formation and Catalytic Functionality of Synthetic Polymer-Noble Metal Colloid

Abstract: Colloidal dispersions of noble metals in synthetic polymers are prepared by reduction with alcohol. Reflux of a solution of rhodium(III) chloride and poly(vinyl alcohol) (PVA) in a methanol-water mixed solvent under argon or air for 4 hr gives a homogeneous solution of colloidal dispersion of rhodium (Rh-PVA-MeOH/H2O). The particle size of metallic rhodium is distributed n a narrow range of 30-70 A, and the average diameter is 40 A. The formation of colloidal rhodium proceeds through three steps: coordination of poly(vinyl alcohol) to rhodium(III) ion, reduction with methanol to form small particles (8 A in diameter), and growth of the small particle to large particle (40 A in diameter). Polyvinylpyrrolidone (PVP) and poly(methyl vinyl ether) (PMVE) can be used in place of poly(vinyl alcohol) and result in colloidal dispersions, respectively, similar to Rh-PVA-MeOH/H2O. Colloidal dispersions in nonaqueous solvent can be prepared by using ethanol instead of methanol-water (Rh-PVP-EtOH) and by usin...

Process for separating organic liquid solutes from their solvent mixtures

Abstract: Process and apparatus for extracting an organic liquid from an organic liquid solute/solvent mixture. The mixture is contacted with a fluid extractant which is at a temperature and pressure to render the extractant a solvent for the solute but not for the solvent. The resulting fluid extract of the solute is then depressurized to give a still feed which is distilled to form still overhead vapors and liquid still bottoms. The enthalpy required to effect this distillation is provided by compressing the still overhead vapors to heat them and indirectly to heat the still feed. The process is particularly suitable for separating mixtures which form azeotropes, e.g., oxygenated hydrocarbon/water mixtures. The energy required in this process is much less than that required to separate such mixtures by conventional distillation techniques.

[3] Measurements of preferential solvent interactions by densimetric techniques

Abstract: Publisher Summary This chapter discusses densimetric techniques to measure preferential solvent interactions. The determination of preferential interactions by densimetry requires the measurement of the density increment under two sets of circumstances namely, at constant m3 and at constant μ3. The chapter provides the formula for density increment measured under conditions at which the molal concentrations of diffusible species are kept identical in the solvent and the macromolecule solution. This results in a partial specific volume of the macromolecule in the given solvent without any consideration of interactions between it and components of the solvent. This is referred to as the “partial specific volume at constant molality.” Operationally, this is done by measuring the densities of pure solvent and of a protein solution dissolved in it. The chapter provides formula for density increment measured under conditions at which the chemical potential of component is kept identical in the solvent and the macromolecule solution. This results in an apparent partial specific volume of the macromolecule in chemical equilibrium with solvent components. This is referred to as the “partial specific volume at constant chemical potential.” Operationally, this is obtained by bringing the macromolecule solution to dialysis equilibrium with solvent and measuring the densities of the dialyzed protein and the dialysate.

Micellar Solubilization of Proteins in Aprotic Solvents and their Spectroscopic Characterisation

Abstract: The quaternary ammonium salt methyl-trioctylammonium chloride enables the transfer of α-chymotrypsin, trypsin, pepsin and glucagone from water to cyclohexane. Reversed micelles, whose polar core solubilizes both protein and water, are probably formed in the apolar phase. The influence of various parameters on the phase transfer (concentration, pH, solvent, temperature, etc.) has been investigated. Absorption, fluorescence and circular dichroism studies of the biopolymers in the cyclohexane system have been carried out. For trypsin and chymotrypsin, the CD. signal in the 200 nm region is very similar in water and in cyclohexane, which suggests that the polypeptide folding is not substantially different in the two phases. The fluorescence quantum yield is always much larger in the cyclohexane phase than in water. The longer wavelength region of the UV. absorption spectrum is slightly red-shifted relative to water, and a band at 225 nm, probably arising from the aromatic chromophore, is apparent in the organic phase. Reasons for these spectral perturbations are discussed. The enzymes transferred from water into cyclohexane phases can be continuously retransferred into a second water phase. The possible relevance of this ‘double transfer’ as a model for the vectorial transport of biopolymers or a separation technique is discussed.

Sweetening of sour natural gases by mixed-solvent absorption: Solubilities of ethane, carbon dioxide, and hydrogen sulfide in mixtures of physical and chemical solvents

Abstract: Solubilities of ethane, carbon dioxide, and hydrogen sulfide have been measured in propylene carbonate, N-methyl-2-pyrrolidone and tetramethylene sulfone (sulfolane); and in mixtures of these physical solvents with monoethanolamine and diglycolamine, in the range −10 to 100°C. Thermodynamically consistent equations are given for gas absorption with chemical reaction at equilibrium. Henry's law describes physical equilibrium between the acidic gas in the vapor phase and free acid solute in the liquid phase. Equilibrium constants describe chemical equilibria for the absorbed gas and the chemical solvent. Preliminary design calculations for sweetening natural gases by absorption with mixed solvents suggest that, under some circumstances, mixed-solvent absorption may be more economical than using conventional aqueous alkanolamine.

Linear solvation energy relationships. Part 3. Some reinterpretations of solvent effects based on correlations with solvent π* and α values

Abstract: Solvent polarity and hydrogen bonding effects on a number of physical and chemical properties and reaction parameters are unravelled and rationalized by means of the solvatochromic comparison method and equations of the form XYZ=XYZ0+sπ*+aα, where π* is a measure of solvent polarity and α a measure of solvent hydrogen bond donor acidity. XYZ's considered include ET values for eight electronic spectral transitions, two sets of nitrogen hyperfine splitting constants, a set of fluorescence lifetimes, logarithms of rate constants for four nucleophilic substitution reactions, and the ‘electrophilicity parameter,’E, of Koppel and Palm.

A semiempirical model for the description of solvent effects on chemical reactions

Abstract: — An attempt is made to provide a more rigorous basis for the description of solvent effects on chemical reactions by taking into account the various free energy contributions involved in the transfer of a substrate from the gas to the solution phase. It is shown that the solvent influence on various chemical and physical processes can be represented in a semiquantitative or even quantitative way by means of three parameters, namely the socalled acceptor number, which represents a measure of the electrophilic or acceptor properties of the solvent, the donor number, which represents a measure of the nucleophilic or donor properties of the solvent and the standard free energy of vaporization of the solvent which is related to the free energy required to create holes in the solvent in which the substrates can be accomodated. Protic solvents usually do not obey the relationships obtained for aprotic media and this appears to be due to the varying basicity of the substrates under consideration.

Compounds of Alkali Metal Anions

Abstract: Anions of sodium, potassium, rubidium, and cesium are stable both in suitable solvents and in crystalline solids. The latter can be prepared either by cooling a saturated solution or by rapid solvent evaporation. Thermodynamic arguments show that alkali metal anions can probably exist in saturated solutions of the alkali metals in any compatible solvent, but that below saturation, dissociation into the cation and solvated electrons is favored in highly polar solvents such as ammonia. The key to solvent-free salts of the alkali metal anions is stabilization of the cation by incorporation into a suitable crown or cryptand complex. By using such complexes it also appears possible to produce “electride” salts in which the charge of the complexed cation is balanced by a trapped electron. The chemical, electrical, and optical properties of salts of the alkali metal anions and “electrides” could provide useful applications.

Whole-body autoradiography and allied tracer techniques in distribution and elimination studies of some organic solvents: benzene, toluene, xylene, styrene, methylene chloride, chloroform, carbon tetrachloride and trichloroethylene.

Abstract: Whole-body autoradiography has been used to study the distribution and fate of 14C-labeled benzene, toluene, xylene, styrene, methylene chloride, chloroform, carbon tetrachloride and trichloroethylene in mice after inhalational exposure. Total radioactivity, including the volatile part of the solvents were registered by autoradiography of dried, evaporated tape-fastened sections. In addition, dried, evaporated tape-fastened sections were extracted with water, trichloroacetic acid and a series of organic solvents and autoradiographed to register organs where metabolites were firmly bound. In another facet of the study, the quantitative elimination of the solvents and their metabolites via various routes was investigated. The expiration of unchanged solvents was subject to mathematical and computerized compartmental pharmacokinetic analysis. All solvents were rapidly taken up in fatty and nervous tissues where they were retained for different periods of time largely dependent on their fat solubility. Unexpectedly long retention times were noted for the chlorinated solvents, particularly for chloroforn, which showed a specific long-term retention in the cerebellum, meninges and spinal nerves, indicating interactions with specific nervous tissue receptors. Solvent metabolites appeared rapidly in several organs, mainly the liver and kidney, and were excreted both via urine and bile. Toluene and xylene metabolites were completely extractable whereas firmly bound metabolites were registered after inhalation of benzene, styrene and all chlorinated solvents, notably in the liver and kidney but also in the bronchi of the lung. Three-compartment pharmacokinetics were observed for the majority of the solvents selected for study although a two-compartment model was found to fit the elimination rate curves for styrene, methylene chloride and chloroform in the exhaled air. The fat solubility of the solvents was found to influence their pharmacokinetics since lower rate constants were generally obtained for the expiration of more fat soluble solvents.

The solvent effect on di‐tert‐butyl nitroxide. A dipole–dipole model for polar solutes in polar solvents

Abstract: New measurements of the solvent effect on the nitrogen hyperfine coupling constant of di‐tert‐butyl nitroxide are reported. These, together with literature data, are used to test various models for the solvent effect. At the Huckel level of approximation, aN is a linear function of the applied electric field. Thus various reaction field theories may be considered. The widely used Onsager reaction field does not account for the effects of the more polar solvents or for the differences between polar and nonpolar solvents. The Wertheim and Block–Walker reaction fields are better, especially for very polar solvents. However none of these continuum reaction fields is entirely satisfactory theoretically or experimentally. We propose a dipole–dipole model for polar solvents which is superior to the continuum models. From the dipole–dipole model, we suggest that the quantity μρ/M is a convenient linear parameter for polar solvent effects, the factors being solvent dipole moment, density, and molecular weight. The...

Method for producing heavy crude

Abstract: A process for the in situ recovery of viscous oil from a subterranean formation is disclosed. Steam is injected into the formation via a well, permitted to soak, and heated fluids including heated viscous oil are produced sufficient to create a substantial fluid mobility in the formation. Then a hydrocarbon solvent having a low concentration of low molecular weight paraffinic hydrocarbons is injected into the formation, and another steam injection, soak and oil production cycle is performed to recover significant additional quantities of oil.

Transformation of steroids by gel-entrapped Nocardia rhodocrous cells in organic solvent

Abstract: Whole cells of Nocardia rhodocrous were immobilized by entrapment with photo-crosslinkable resin prepolymers or urethane prepolymers of either hydrophilic or hydrophobic character, and their activity in converting 3β- hydroxy-Δ5 to corresponding 3-keto-Δ4 in an appropriate organic solvent system (e.g., a water-saturated mixture of benzene and n-heptane (1∶1 by volume)) was studied. Although both hydrophilic gel-entrapped cells and hydrophobic gel-entrapped cells could transform dehydroepiandrosterone to 4-androstene-3, 17-dione, the latter showed a significantly higher activity than the former. In the cases of the oxidation of cholesterol, β-sitosterol and stigmasterol to the corresponding 3-keto-Δ4-steroids, only hydrophobic gel-entrapped cells exhibited the catalytic activity. The cells entrapped in adequate hydrophobic gels had steroid transforming activity comparable to that of the free counterparts. The operational stability was improved by the entrapment, especially in the case of the transformation of dehydroepiandrosterone. The activity of the gel-entrapped cells was found to correspond closely to the partition coefficients of substrates between the gels and the external solvent.

Potentiometric investigation of dialuminum heptachloride formation in aluminum chloride-1-butylpyridinium chloride mixtures

Abstract: : The solvent acid-base properties of AlCl3: 1-butylpyridinium chloride melts from 22 to 10 to 06 to 10 molar ratios, respectively, have been investigated by potentiometry An equilibrium constant K3 for the dissociation reaction (Author)

Reversible photo-oxidation of zinc tetraphenylporphine by benzo-1,4-quinone

Abstract: Zinc tetraphenylporphine shows fairly weak fluorescence and phosphorescence but intense, long-lived triplet absorption. Benzo-1,4-quinone quenches the singlet and triplet excited states of ZnTPP and the quenching probability increases with increased polarity of the solvent. Quenching leads to formation of a complex which, for the triplet reaction in toluene, is sufficiently long-lived to be observed by flash spectroscopy. In polar solvents, quenching leads to production of separated ions, the yield being a function of the solvent dielectric constant.

An interpretation of a general scale of solvent polarities. A simplified reaction field theory modification

Abstract: The existence of linear relationships of good quality involving the effects of polar solvents on different properties of neutral, highly polar solutes is rationalized in terms of the reaction field theory. It is shown that the treatment of Block and Walker in which the dielectric constant at a distance r from the center of the solute cavity is taken as t(r) = where en is the bulk dielectric constant, gives a satisfactory description of experimental results involving NMR shift data, solvation free energies, activation free energies, T-T* transitions, and molecular dipole moments. It is concluded that (1) the short-lived clustering of polar solvent molecules around dipolar solutes is a significant factor to be considered in the study of solvent effects on dipolar solutes; (2) the scope of the reaction field formalism can be extended to solutes of high polarity provided allowance is made for dielectric saturation of the polar solvent molecules.