Solvent excess function

Similarly, molar excess functions have been determined for various thiazole-solvent binary mixtures (Table 1-46) (307-310). 

Considerable information concerning structural effects on aqueous salt solutions has been provided by studies of the properties of mixed solutions (Anderson and Wood, 1973). In a mixed salt solution prepared by mixing YAm moles of a salt MX (molality m) with Yhm moles of a salt NX (molality m) to yield m moles of mixture in 1 kg of solvent, if W is the weight of solvent, the excess Gibbs function of mixing Am GE is given by (19) where GE is the excess function for... 

In these mixtures, the excess function GE is positive while T SE is large and negative such that T SE > //E. Co-solvents forming such mixtures include monohydric alcohols, acetone, tetrahydro-furan and dioxan which are often used in kinetic studies. 

Absorption methods give evidence on ion pairs but do not necessarily yield the overall association constants required by the thermodynamic excess functions. However, they furnish essential contributions to the elucidation of solvent-solvent and ion-solvent interactions and are the basis for most of the semi-empirical interaction scales usually applied. 

The dissolution of a gas in a liquid is basically a two-stage process. First a cavity must be formed within the solvent of sufficient size to accommodate the solute molecule, and this step is followed by the insertion of the solute within the solvent cavity with a resultant change in the energy of the system which depends primarily on the magnitude of the solvent-solute interactions. This second stage of the process is now reasonably well understood in terms of the statistical mechanical theories of fluid mixtures discussed briefly in previous sections, although accurate predictions of thermodynamic excess functions are only possible in a limited number of cases when auxiliary measurements enable explicit values of and x to be estimated. It is, as yet, not possible to predict gas solubilities with comparable confidence. 

Chain entanglement and normal mode motions of (PDMS) in solvent solutions have been reported together with segmental diffusions. Thermodynamic data on solutions of (PDMS) using a new experimental technique for measurement of P-V-T relationships have been reported, and expressions for thermodynamic excess functions for mixtures of non-polar polymer/solvent have been proposed that give improved fit to the Flory theoretical treatment. ... 

It must be underlined that this conversion should be performed in any study using the primitive MSA because, in this framework, the thermodynamic excess functions are calculated at the MM level. The MM framework is characterized by two features the solvent is regarded as a continuum which manifests itself through its permittivity, and the thermodynamic properties are calculated at constant solvent chemical potential. Although the effect of the conversion is negligible at relatively low concentrations it becomes significant as concentration is increased, typically above 1-2 mol/kg [35]. 

All the investigations cited so far have been in aqueous solution medium dependence of dissociation rate constants in binary aqueous solvents (cosolvents methanol, r-butyl alcohol, 1,2-ethanediol, 1,2,3-propanetriol, and sucrose) has been reported for the 4-cyanopyridine and 4,4 -bipyridyl penta-cyanoferrates(II). For water-rich media (IQi lD < 16.5), plots of logarithms of rate constants against mole fraction organic component are linear, against 1/D almost linear. Slopes differ greatly between cosolvents, but results can be correlated quite satisfactorily with a three-parameter equation incorporating acidity and basicity parameters and the excess function... 

The rate (kinetics) and the completeness (fraction dissolved) of oxide fuel dissolution is an inverse function of fuel bum-up (16—18). This phenomenon becomes a significant concern in the dissolution of high bum-up MO fuels (19). The insoluble soHds are removed from the dissolver solution by either filtration or centrifugation prior to solvent extraction. Both financial considerations and the need for safeguards make accounting for the fissile content of the insoluble soHds an important challenge for the commercial reprocessor. If hydrofluoric acid is required to assist in the dissolution, the excess fluoride ion must be complexed with aluminum nitrate to minimize corrosion to the stainless steel used throughout the facility. Also, uranium fluoride complexes are inextractable and formation of them needs to be prevented. 

N -Heterocyclic Sulfanilamides. The parent sulfanilamide is manufactured by the reaction of A/-acetylsulfanilyl chloride with excess concentrated aqueous ammonia, and hydrolysis of the product. Most heterocycHc amines are less reactive, and the condensation with the sulfonyl chloride is usually done in anhydrous media in the presence of an acid-binding agent. Use of anhydrous conditions avoids hydrolytic destmction of the sulfonyl chloride. The solvent and acid-binding functions are commonly filled by pyridine, or by mixtures of pyridine and acetone. Tertiary amines, such as triethylamine, may be substituted for pyridine. The majority of A/ -heterocycHc sulfanilamides are made by simple condensation with A/-acetylsulfanilyl chloride and hydrolysis. 

Astringents are designed to dry the skin, denature skin proteins, and tighten or reduce the size of pore openings on the skin surface. These products can have antimicrobial effects and are frequendy buffered to lower the pH of skin. They are perfumed, hydro-alcohoHc solutions of weak acids, such as tannic acid or potassium alum, and various plant extracts, such as bitch leaf extract. The alcohol is not only a suitable solvent but also helps remove excess sebum and soil from the skin. After-shave lotions generally function as astringents. 

Ester functions are not saponified under these ring opening conditions. However, a trans-a-acetoxy function hinders the epoxide opening reaction and a noticeable decrease in yield is observed in comparison to the cw-a-acetoxy isomer. The ring opening reaction is also dependent on the concentration of sulfuric acid. Polymer formation results when the acid concentration is too low and the reaction is markedly slower with excessive concentrations of acid. A 0.5% (vol./vol.) concentration of acid in DMSO is satisfactory. Ring opening does not occur when ethanol, acetone, or dioxane are used as solvent. 

The importance of the solvent, in many cases an excess of the quatemizing reagent, in the formation of heterocyclic salts was recognized early. The function of dielectric constants and other more detailed influences on quatemization are dealt with in Section VI, but a consideration of the subject from a preparative standpoint is presented here. Methanol and ethanol are used frequently as solvents, and acetone,chloroform, acetonitrile, nitrobenzene, and dimethyl-formamide have been used successfully. The last two solvents were among those considered by Coleman and Fuoss in their search for a suitable solvent for kinetic experiments both solvents gave rise to side reactions when used for the reaction of pyridine with i-butyl bromide. Their observation with nitrobenzene is unexpected, and no other workers have reported difficulties. However, tetramethylene sulfone, 2,4-dimethylsulfolane, ethylene and propylene carbonates, and salicylaldehyde were satisfactory, giving relatively rapid reactions and clean products. Ethylene dichloride, used quite frequently for Friedel-Crafts reactions, would be expected to be a useful solvent but has only recently been used for quatemization reactions. ... 

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