Dielectric behavior 295 acids

The trends of variation of the activation parameters are correlated with the solvation mechanism and dielectric behavior of the medium. Thus, AH, AG and A5 for the acidic resin-catalyzed hydrolysis of isopropyl acetate were calculated using the Wynne-Jones and Eyr-... 

It might be useful in some cases to raise the dielectric constant of mixed solvents by addition of suitable substances and it is known that dipolar molecules such as amino acids do so in pure water. These amino acids are virtually insoluble in nonpolar solvents but they dissolve readily in aqueous salt solutions and in most mixed solvents according to their highly polar structure. Most of what is known about their dielectric behavior concerns aqueous solutions, in which they were studied up to concentrations near saturation. 

The dielectric properties of water and oil differ radically. A high water concentration in food systems greatly increases its dielectric properties. Oil, however, contributes relatively little to the dielectric behavior of a food system (1). Consequently, in the 90/10 oil/water mixture, the microwave energy was directed primarily at the 10% aqueous phase. Acids added to this 90/10 mixture will partition into this aqueous phase to the extent of their relative solubility in the two phases. Greatest losses were observed for acetic acid which exhibits the greatest solubility in water and was concentrated in the aqueous phase. Losses of the more nonpolar acids, i.e. caproic, were also much greater in microwave samples. Losses of the relatively... 

Association constant — Solvents having a low dielectric constant (e.g., benzene er = 2.29) cannot split protons from acids. The acid/base behavior in these solvents is based on association reactions between acidic and basic components in the solution according to ... 

The dielectric constant is a property of major concern in understanding acid-base behavior in various solvents. When the dielectric constant of a solvent is low, ion association and homoconjugation can take place, resulting in modification of otherwise simple proton transfer reactions. 

The mechanical 3 peak in the dried acid occurs at approximately 20°C. The water sensitivity of the 3 peak position is remarkable (46). This 3 peak migrates to lower temperatures with increasing water concent and eventually merges with the Y peak. The depression of the 3 peak temperature with moisture content is also found in the dielectric measurement on the same Nafion acid. Similar behavior was observed for the salts, the decrease in temperature of 3 peak position with increasing water content being perhaps even more drastic. 

The adhesive properties of epoxy resins coupled with their dielectric behavior have made them attractive to the electronic industry. The evaluation of thermally cured rubber modified epoxy thermosets has been the subject of recent studies (1, 2), which dealt with the dependence of morphology on the curing parameters, e.g., catalyst, cure schedule, time of gelation, etc. This work utilizes one of the new series of photocationic initiators (PCI) developed by Crivello, et al (3) which are presently commercially available. These onium salts initiate the reaction by absorbing the actinic radiation, generating radicals and producing a protonic acid. The radicals can lead to polymerization of olefinic moieties (4) while the acid initiates the polymerization of the epoxy groups (3). 

Dielectric behavior of poly(amino acid) solids has also been studied[27-29]. In this chapter we will present... 

The presence of surface treatments (coupling agents, stearic acid derivatives, fiber sizings, elastomeric additives) and of adsorbed water complicates the dielectric behavior, as the new interfaces may give rise to additional interfacial and ionic and dipolar relaxation processes (see the examples). 

This material, commercialized by Du Pont as Kapton M (vi), exhibits excellent thermal stability and good dielectric behavior. The poly(amic acid) solution in N-methyl pyrrolidone is also... 

The solubility of some salts in pyridine and other amines of low dielectric constant is more readily understood in terms of acid-base behavior. The metallic ion, being acidic, coordinates molecules of solvent about it. Silver salts in pyridine, ethylenedia-mine, and other amines show abnormar conductance curVes. 

In this contribution, we describe and illustrate the latest generalizations and developments[1]-[3] of a theory of recent formulation[4]-[6] for the study of chemical reactions in solution. This theory combines the powerful interpretive framework of Valence Bond (VB) theory [7] — so well known to chemists — with a dielectric continuum description of the solvent. The latter includes the quantization of the solvent electronic polarization[5, 6] and also accounts for nonequilibrium solvation effects. Compared to earlier, related efforts[4]-[6], [8]-[10], the theory [l]-[3] includes the boundary conditions on the solute cavity in a fashion related to that of Tomasi[ll] for equilibrium problems, and can be applied to reaction systems which require more than two VB states for their description, namely bimolecular Sjy2 reactions ],[8](b),[12],[13] X + RY XR + Y, acid ionizations[8](a),[14] HA +B —> A + HB+, and Menschutkin reactions[7](b), among other reactions. Compared to the various reaction field theories in use[ll],[15]-[21] (some of which are discussed in the present volume), the theory is distinguished by its quantization of the solvent electronic polarization (which in general leads to deviations from a Self-consistent limiting behavior), the inclusion of nonequilibrium solvation — so important for chemical reactions, and the VB perspective. Further historical perspective and discussion of connections to other work may be found in Ref.[l],... 

Equation (24) renders intelligible the behavior of the dielectric constant of dipolar ions in polar solutions. It explains the linear increase of D with concentration, since changes in partial molar volumes, only slightly dependent on concentration, can only affect the DyVi term. It also explains the nearly identical values of D of the amino acids of the same moment, and the fact that D of a given amino acid is insensitive to changes in the dielectric constant of the solvent, for the change of solvent can directly affect 8 only through the term D V2. 

Table VI summarizes the effect of heating medium on the loss of acids after 3 minutes of microwave heating. Loss of volatile acids varied widely dependent on the microwave medium. Acetic and caproic acids had losses ranging from 20-80% and 0-73%, respectively, depending on medium composition. The dielectric property, specific heat, or other physical/chemical properties of individual flavor compounds can provide valuable insight into the potential behavior of these compounds during the microwave process. The dielectric property of the total food system and the affinity of the flavor compound for the microwave medium, however, were primarily responsible for the behavior of these flavor compounds during microwave heating.

The solubility of solids in liquids is typically attributed to the dielectric of the solvent, however this does not explain the situation here as is seen in Table 2. The low dielectric constant of the THF/MeOH system should make it a poor solvent for polyamic acid. Consequently, there must be other factors contributing to PAA solubility however, the causes of this solubility behavior have not been elucidated at this time. 

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