Showing papers on "Solvent published in 1974"

Solvation of ions. XIX. Thermodynamic properties for transfer of single ions between protic and dipolar aprotic solvents

Abstract: Standard molar free energies, enthalpies and entropies of transfer of some uni-univalent electrolytes from water to methanol, N-methylformamide, formamide, dimethyl sulphoxide, N,N-dimethyl- formamide, propylene carbonate, sulpholane, N-methylpyrrolidone and acetonitrile are presented. They have been divided into the corresponding thermodynamic properties for single ions by means of extrathermodynamic assumptions. Changes in the chemistry of anions on transfer from protic to dipolar aprotic solvents are mainly a function of enthalpy changes. There is a substantial loss of entropy on transferring both anions and cations from water to non-aqueous solvents. Entropies of transfer can be interpreted in terms of ordering and disordering solvent molecules and a uniquely extensive water structure. Evidence for solvation of the first and second kind in water is presented. Enthalpies of transfer from water are exothermic for cations but endothermic for many anions.

Diffusion in Polymer Gel Implants

Abstract: Crosslinked polyacrylamide and polyvinylpyrrolidone gels have been used to subcutaneously implant 125I-labeled immunoglobulin, 125I-labeled luteinizing hormone, 125I-labeled bovine serum albumin, 125I-labeled insulin, [3H]prostaglandin F2α, and Na125I into hamsters From the rates of absorption of the solutes, their diffusion coefficients were determined The diffusion coefficients showed a logarithmic dependence on implant polymer concentration and solute molecular weight Release of the solutes from gel preparations incubated 10 mM phosphate buffer (pH 72) at 37° revealed a similar relationship between solute diffusion coefficient, molecular weight, and the concentration of polymer A general equation was derived that gives the expected diffusion coefficient of a substance in a polymer gel from its molecular weight, diffusion coefficient in solvent, and polymer concentration of the gel

Treatment of wells

Abstract: A method of treating a subterranean formation surrounding a well wherein a solvent including a C4 to C10 alkyl ether of polyglycol ether containing from 10 to 22 carbon atoms per molecule is injected into the formation. The solvent improves permeability to the formation adjacent the wellbore. The solvent may be used as a preflush or afterflush for, or in combination with, other treating agents; or it may be used as the sole essential treating agent.

In situ recovery of hydrocarbons from tar sands

Abstract: Hydrocarbon products from viscous tar sands are recovered by continuously injecting a hot solvent containing relatively large amounts of aromatics into the formation. Alternatively, steam and solvent are cyclically and continuously injected into the formation to recover the values. The last stimulation is by steam so that solvent is recovered. A third alternative is to continuously inject a mixture of steam and solvent vapors and liquid into the formation. In all cases, the solvent, except perhaps for startup, is produced at the site, as in a conventional topping unit, which alternatively is combined with a conventional visbreaking or reforming unit to increase the volume and/or aromaticity of the solvent produced.

Respiratory elimination of organic solvents in man

Abstract: Respiratory elimination of benzene, toluene, n-hexane, trichloroethylene, acetone, ethyl acetate and ethyl alcohol were studied after exposure in human volunteers to those solvents. 1. Solvent concentration in expired air decreased rapidly with time after the cessation of exposure and the decrease was expressed as an equation. Ethyl acetate and ethyl alcohol in expired air decreased faster than did other organic solvents. The decrease was very slow in acetone. 2. Large amounts of retained acetone, benzene and n-hexane were eliminated through the lungs as unchanged solvents, while the amount of eliminated ethyl acetate was almost negligible. 3. The ratio of respiratory elimination to the inhaled (environmental) organic solvent suggested that the determination of respiratory concentration is helpful for estimating environmental benzene, acetone, trichloroethylene and toluene concentration.

An approach to the development of cellulose acetate ultrafiltration membranes

Abstract: The film-casting solution consisted of a mixture of cellulose acetate, acetone, and aqueous magnesium perchlorate [Mg(ClO4)2:H2O = 1:8.5], designated as polymer P, solvent S, and nonsolvent N, respectively. Using the composition P:S:N = 17: 69.2: 13.8 as reference, films were obtained from 19 different casting solutions in which the weight ratios S/P, N/S, and N/P were varied in different directions. The casting solution temperature was 0°C, and solvent evaporation period during film formation was minimum in most cases. The effects of variations of casting solution temperature and solvent evaporation period were also briefly studied. Reverse osmosis experiments with resulting membranes were carried out at 100 psig using 200 ppm NaCl–H2O as the feed solution. Decrease in S/P, increase in N/S, and increase in N/P in the casting solution, decrease in temperature of the casting solution, and increase in solvent evaporation period tend to increase the size of pores on the surface of resulting membranes in the ascast condition. Increase in S/P in the casting solution, and increase in the temperature of the casting solution tend to increase the effective number of pores on the membrane surface. These results offer definitive physicochemical criteria in terms on solution structure–evaporation rate concept for developing useful cellulose acetate ultrafiltration membranes.

Respirator Cartridge Efficiency Studies: V. Effect of Solvent Vapor

Abstract: We have determined the service lives of organic vapor respirator cartridges for 121 solvent vapors and gases including aromatics, alcohols, acetates, alkanes, ketones, amines, and chlorinated materials. We passed the vapor and air mixtures through the cartridges and monitored the downstream concentration with a flame ionization detector (FID). Monitoring continues until the cartridge is completely saturated. We compared breakthrough times to values calculated from the adsorption isotherm and Mecklenburg equation and obtained reasonable agreement. In general, the activated carbon has greater affinity for the less volatile materials. Also, the higher the boiling point of the solvent, the greater is the weight of solvent adsorbed. Water vapor, in general, decreases the amount of solvent vapor adsorbed, especially of the more volatile solvents and those soluble in water. The effect of concentration on breakthrough time was briefly investigated and found to conform to the basic Freundlich equation.

HR-NMR study of formation and structure of the stereocomplex of poly(methyl methacrylate) in solution

Abstract: From high-resolution NMR spectra of mixtures of solutions of isotactic and syndiotactic poly(methyl methacrylate), the content p of the associated stereocomplex was determined. From the values of p, the minimum length of associated syndiotactic sequences was found to be ca. 10 monomeric units in aromatic solvents and ca. 3 such units in CCl4 and CD3CN. In the associated stereocomplex the ratio of monomeric units in isotactic and syndiotactic sequences is (iso/syndio) = 1:1,5; the process of dissociation of the stereocomplex with increasing temperature is reminiscent of the melting of microcrystallites. The melting point of associated segments in a given solvent increases with the length of the associated sequences. Aus hochaufgelosten Kernresonanzspektren wurde der Gehalt p an assoziiertem Stereokomplex in Losungen von isotaktischem und syndiotaktischem Poly(methyl methacrylat) bestimmt. Mit Hilfe der p-Werte wurde festgestellt, das in aromatischen Losungsmitteln die minimale Lange der assoziierten syndiotaktischen Sequenzen ca. 10 Monomereinheiten betragt, in CCl4 und CD3CN ist die minimale Lange ca. 3 Monomereinheiten. Im assoziierten Stereokomplex ist das Verhaltnis der Monomereinheiten von isotaktischen und syndiotaktischen Sequenzen (iso:syndio) = 1:1,5; die Dissoziation des Stereokomplexes erinnert bei Erhohung der Temperatur an das Schmelzen von Mikrokristallen. Der Schmelzpunkt der assoziierten Segmente steigt in einem gegebenen Losungsmittel mit der Lange der assoziierten Sequenzen.

Determination of empirical parameters of solvent polarity E T in binary mixtures by solvatochromic pyridinium-N-phenol betaine dyes

Abstract: Empirical parameters of solvent polarity E T of some pure solvents and their binary mixtures (especially with CCl4 and CHCl3) were determined spectrophotometrically using solvatochromic pyridinium-N-phendl betaine dyes. Calibration curves are given for 16 binary solvent mixtures. The obtained E T values show that a synergetic polarity effect appears with the organic solvents containing C=O, P=O, and S=O groups in the mixture with chloroform. With these binary mixtures the increase of E T values results from the formation of 1∶1 complexes X=O... H-CCl3 by means of hydrogen bonding. Increasing number of methylene groups in the chain increases the synergism with these type of complexes.

Structure of aggregates and helix–coil transition of polypeptides by dielectric measurements. I. Poly-γ-benzyl-L-glutamate in dioxane and dioxane–dichloroacetic acid

Abstract: Dielectric dispersion measurements on poly-γ-benzyl-L-glutamate (PBLG) in dioxane and dioxane–dichloroacetic acid (DCA) mixtures in the frequency range 200 Hz–2 MHz were made in order to study the structure of molecular aggregates. The structure of aggregates is explained on the basis of the variation of dipole moment and relaxation time with degree of aggregation. PBLG was found to form linear head-to-tail-type aggregates in dioxane. These aggregates gradually reduce in size without loosing their α-helical structure during the process of disaggregation obtained by either adding DCA to the solution in dioxane or by heating. It was confirmed that the addition of 30 wt % DCA completely destroys the aggregation of PBLG in dioxane at 30°C. Thermal disaggregation, however, was not complete even at a temperature approaching the boiling point of the solvent. A reaction scheme for aggregation is proposed and equilibrium constants are calculated at various stages of aggregation. The enthalpy of aggregate formation is found to be −3 kcal/mol. Results of optical rotatory dispersion measurements of the helix–coil transition in this system are also presented.

Carboxylation of active methylene compounds using the reagent of 1,8-diazabicyclo(5.4.0)-7-undecene and carbon dioxide

Abstract: Various active methylene compounds were carboxylated by employing the reagent system, 1,8-diazabicyclo(5.4.0)-7-undecene and carbon dioxide, in organic solvents or without solvent at room temperature.

Solvent exposure of specific nuclei of angiotensin II determined by NMR solvent saturation method

Abstract: CONFORMATIONAL analysis of peptides in solution by nuclear magnetic resonance (NMR) spectroscopy generally involves determination of the relative exposure to solvent of specific NH hydrogens1–4. The four methods used so far are based on: (1) rates of NH proton exchange with labile hydrogens of the solvent5–6; (2) temperature dependence of chemical shifts of NH resonances7–8; (3) dependence of NH chemical shifts on the composition of a suitable solvent mixture3,9–11, and (4) degree of resonance broadening when a paramagnetic substance is added12. Each method has limitations. Proton exchange rates reflect not only exposure to solvent, but also proximity to functional groups of the peptide which catalyse exchange. Factors which determine the temperature dependence of NH chemical shifts are as yet poorly understood. Changes in solvent composition can alter the conformation of the peptide11. Paramagnetic ions may associate preferentially with the solvent or with specific sites on the peptide.

Heated multiple solvent method for recovering viscous petroleum

Abstract: Viscous petroleum may be recovered from viscous petroleum-containing formations including tar sand deposits by contacting the formation with a heated multiple-component solvent for the petroleum. At least one solvent component is normally gaseous material such as methane, ethane, propane or butane and at least one component is normally liquid, such as pentane and higher molecular weight hydrocarbons. The solvent mixture is heated to a temperature in excess of ambient temperature, and preferably from 100° to 500° F. prior to injection into the formation. The multiple solvent is introduced under sufficient pressure that it is substantially all liquid at the injection conditions. Recovery of petroleum and solvent may be from the same well as is used for injection or from a remotely located well. When the pressure in a portion of the formation contacted by the solvents is reduced below the bubble point pressure of the solvent-bitumen solution, the solvents vaporize to provide a solution gas oil recovery mechanism. The normally liquid components dissolve in the petroleum and reduce the petroleum viscosity.

Phenolic resin-polyisocyanate binder systems containing dialkyl phthalate solvents

Abstract: Dialkyl phthalate esters, particularly those of ortho-pthalic acid, are used as part or all of the solvent in solvent systems for two-package resin compositions comprising a phenolic resin component and a polyisocyanate hardener package and, in threepackage systems for, the basic catalyst used.

Aromatic bis(ether phthalis anhydride) compounds

Abstract: Aromatic bis(ether anhydride)s are prepared from the hydrolysis of the reaction product of a nitro-substituted phenyl dinitrile with a metal salt of a dihydroxy aryl compound in the presence of a dipolar aprotic solvent.

Powdered cleaning composition of urea-formaldehyde

Abstract: A powdered cleaning composition particularly effective in removing soil from carpets comprising solid polymeric urea-formaldehyde particles of 10 to 105 microns in size and a solvent chosen from water, high boiling hydrocarbon or chlorinated hydrocarbon solvents, C1 to C4 aliphatic alcohols and mixtures of these.

Carbon-13 Magnetic Resonance Evaluation of Polypeptide Secondary Structure and Correlation with Proton Magnetic Resonance Studies

Abstract: With the use of appropriately chosen solvent pairs it is demonstrated that solvent dependence of peptide carbonyl carbon resonances can be correlated with polypeptide secondary structure. Solvent titrations show the peptide carbonyl which is intramolecularly hydrogen bonded to exhibit less chemical shift on going from a dimethylsulfoxide solution to a solution containing a solvent which is a good proton (or deuteron) donor. Effective solvent systems are dimethylsulfoxide paired with water, trifluoroethanol, or methanol. This approach is demonstrated with the pentapeptide of elastin.