Solid equilibria involving

For 3-hydroxyisoxazol-5-ones 220, a complex equilibrium involving six potential tautomers was considered [75T1861 76AHC(S1), p. 449], In the solid, the tautomeric forms 220b and 220c were observed, while in solution (DMSO, chloroform, ethanol) the zwitterionic tautomer 220f is regarded as the major form (Scheme 73). 

Five possible isomers may coexist in the tautomeric equilibrium involving 2,6-diazidopurine 343 (Scheme 135). It was concluded (75UK1028) that diazide 343AA is the sole form in the solid state and in solutions in acetic and trifluoroacetic acids. In DMSO solution, two additional tautomers, 343AT and 343ATS were also observed. 

A number of metals have the ability to absorb hydrogen, which may be taken into solid solution or form a metallic hydride, and this absorption can provide an alternative reaction path to the desorption of H,. as gas. In the case of iron and iron alloys, both hydrogen adsorption and absorption occur simultaneously, and the latter thus gives rise to another equilibrium involving the transfer of H,<,s across the interface to form interstitial H atoms just beneath the surface ... 

The starting materials are solid Pbl2 and H2 O. These are the only major species present before any solid dissolves. The only equilibrium involving these reactants is the solubility reaction. Solid Pbl2 dissolves in water to produce its ions in solution, Pb and I ... 

The determination of adsorption isotherms at liquid-solid interfaces involves a mass balance on the amount of polymer added to the dispersion, which requires the separation of the liquid phase from the particle phase. Centrifugation is often used for this separation, under the assumption that the adsorption-desorption equilibrium does not change during this process. Serum replacement (6) allows the separation of the liquid phase without assumptions as to the configuration of the adsorbed polymer molecules. This method has been used to determine the adsorption isotherms of anionic and nonionic emulsifiers on various types of latex particles (7,8). This paper describes the adsorption of fully and partially hydrolyzed PVA on different-size PS latex particles. PS latex was chosen over polyvinyl acetate (PVAc) latex because of its well-characterized surface PVAc latexes will be studied later. 

The worst deviations from the Clapeyron equation occur when one of the phases is a gas. This occurs because the volume of a gas depends strongly on temperature, whereas the volume of a liquid or solid does not. Accordingly, the value of A Vm is not independent of temperature when the equilibrium involves a gas. 

The purpose of this chapter is to outline the simplest methods of arriving at a description of the distribution of species in mixtures of liquids, gases and solids. Homogeneous equilibrium deals with single phase systems, such as electrolyte solutions (e.g., seawater) or gas mixtures (e.g., a volcanic gas). Heterogeneous equilibrium involves coexisting gaseous, liquid and solid phases. 

On the basis of the solution and solid state 15N results, an equilibrium involving the half protonated form of the base in the solution of the complex salt has been identified. The 13C results for the solutions, on the other hand, are very similar to those found for the solid state, and are rather insensitive to salt formation. So it seems that the 15N NMR data provide the most suitable means of investigating the structure of the compounds studied in both solution and the solid state. 

The products from benzotriazole, aldehydes and primary or secondary amines exist in the melt or in solution as equilibrium mixtures of 1- and 2-benzotriazolyl compounds, 99 and 100, whereas the solids are 1-benzotriazoles 99115. The equilibrium involves the resonance-stabilized aminomethyl cation and the delocalized benzotriazolide anion it accounts for the ease with which the bond attached to the benzotriazole moiety is cleaved. 

In contrast to the detonation of gaseous materials, the detonation process of explosives composed of energetic solid materials involves phase changes from solid to liquid and to gas, which encompass thermal decomposition and diffusional processes of the oxidizer and fuel components in the gas phase. Thus, the precise details of a detonation process depend on the physicochemical properties of the explosive, such as its chemical structure and the particle sizes of the oxidizer and fuel components. The detonation phenomena are not thermal equilibrium processes and the thickness of the reachon zone of the detonation wave of an explosive is too thin to identify its detailed structure.[i- i Therefore, the detonation processes of explosives are characterized through the details of gas-phase detonation phenomena. 

So far, only gaseous reactants have been considered. If solids are involved, the terms arising from the activities of the solids are usually omitted and the equilibrium constant includes only the fugacities of the gaseous reactants, e.g. for the reaction... 

One of the most effective methods for evaluating the purity of chemical substances is that involving determination of the freezing point, with appropriate observation of the temperature of the liquid-solid equilibrium as a function of the fraction of sample frozen or melted. 

A similar example, more in line with organic chemistry, was recently described by Dillon and Straw222 the phosphorane 168 is found in solutions, whereas the ionic species 169 and 170 make up the solid. In many cases, the redistribution of substituents between two phosphorane molecules can be ascribed to the existence of a P(IV) P(V) equilibrium involving a phosphonium salt223, as with 171 172. Similarly, the study of the Mitsunobu reaction224 resulted in bringing to light successive equilibria such as 173 174 175 (Scheme 47). 

The reasoning applies generally to (degenerate) N-phase equilibrium involving N mutually immiscible species. Whence the cited result for solids. 

The electrolytic permeability is a property of any solid electrolyte, since a local equilibrium involving ions and electrons is required by - thermodynamics for any conditions close to steady-state or global equilibrium. However, it is possible to optimize the level of permeability, depending on particular applications. In many cases, the permeability is a parasitic phenomenon leading to power losses in - fuel cells and - batteries, lower efficiency of solid-state electrolyzers and -> electrochemi-... 

You are given a heterogeneous equilibrium involving gases and solids. The general form of the equilibrium constant expression for this reaction is... 

Two Schiff bases (A,iV -bis(5-bromosalicylidene)-1,2-diamino-ethane and 7-[( 1 -(5-bromo-2-hydroxyphenyl)methylidene)amino]-4-methyl-coumarin), and two appropriate Schiff-Mannich bases (A,JV-bis(5-bromo-3-[(diethylamino)methyl]salicylidene)-1,2-diaminoethane and 7-[( 1 -(5-bromo-3-[(diethylamino)methyl]-2-hydroxyphenyl)methylidene)amino]-4-methylcoumarin) capable of intramolecular hydrogen bonding have been investigated by multi-nuclear NMR methods in both solid and liquid phases. In all of the compounds under investigation tautomeric equilibrium involving an intramolecular hydrogen bond has been found. In the solid state the tautomeric... 

Isolation of the major component in the pure state from a mixture can be carried out by fractional crystallisation, if only small amounts of that component need to be crystallised out from a system involving liquid-solid equilibrium in which the contaminant tends to concentrate in the liquid phase. The reverse process of fractional melting, however, can sometimes be used to achieve the same objective with greater advantage. Purification by fractional melting requires less effort than that required by repeated crystallisation and it gives the purified product in comparatively high yields also. 

Fractional melting is based on the principle that at any temperature a contaminant is concentrated in the liquid phase, if its addition depresses the freezing point. One specific example will suffice to illustrate how fractional melting makes use of this underlying principle to bring about purification. The example under reference is the isolation of pure isooctane (2, 2, 4-trimethyl pentane) from its mixture with the eutectogenic contaminant, n-pentane. This mixture constitutes a system which involves liquid-solid equilibrium in which the impurity tends to concentrate in the liquid phase. 

This presentation may be viewed as a sampler of a whole group of fixed-bed problems that are concerned with the combination of transport rates with various types of fluid-solid equilibrium. Some of these cases involve chemical reactions, but generally they do not. 

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