Acid-base equilibria temperature effect

Uncatalyzed amidations of acids have been realized under solvent-free conditions and with a very important microwave effect [67 a]. The best results were obtained by use of a slight excess of either amine or acid (1.5 equiv.). The reaction involves thermolysis of the previously formed ammonium salt (acid-base equilibrium) and is promoted by nucleophilic attack of the amine on the carbonyl moiety of the acid and removal of water at high temperature. The large difference in yields (MW > A) might be a consequence of interaction of the polar TS with the electric field (Eq. (15 a) and Tab. 3.6). 

V.L. Cherginets and T.P. Rebrova, The Effect of Temperature on Characteristics of Acid-Base Equilibrium in Medium of Molten Sodium Chloride, Zh. Fiz. Khim. 71 (2004) 1886-1889. 

The authors claim that these associations, which are destroyed in fixed compounds, play an important role in the calculation of Ty.The cases of 1,2,4-triazole-5-thiones 74 [97SA(A)699] and of pyridone dimers 15a-15a and 15a-15b were also studied [96MI(13)65]. (3) The recording of IR spectra in solution at different temperatures to determine the effect of the temperature on Kj-, for instance, in pyrazolinones [83JPR(325)238] and in cytosine-guanine base pairs [92MI(9)881]. (4) The determination of the equilibrium 2-aminopyridine/acetic acid 2-aminopyridinium acetate (see Section III.E) in the acid-base complex was carried out by IR (97NKK100). 

A mechanistic study of acetophenone keto-enol tautomerism has been reported, and intramolecular and external factors determining the enol-enol equilibria in the cw-enol forms of 1,3-dicarbonyl compounds have been analysed. The effects of substituents, solvents, concentration, and temperature on the tautomerization of ethyl 3-oxobutyrate and its 2-alkyl derivatives have been studied, and the keto-enol tautomerism of mono-substituted phenylpyruvic acids has been investigated. Equilibrium constants have been measured for the keto-enol tautomers of 2-, 3- and 4-phenylacetylpyridines in aqueous solution. A procedure has been developed for the acylation of phosphoryl- and thiophosphoryl-acetonitriles under phase-transfer catalysis conditions, and the keto-enol tautomerism of the resulting phosphoryl(thiophosphoryl)-substituted acylacetonitriles has been studied. The equilibrium (388) (389) has been catalysed by acid, base and by iron(III). Whereas... 

This reaction is highly exothermic. If the heat of the reaction is not conducted thru the walls of a closed container at a rate capable of maintaining an equilibrium temperature, an increase in pressure results with an increase in reaction rate, leading to explosive conditions. Acid salts, such as stannic chloride and zinc chloride, and bases, such as alkali metal hydroxides, either solid or in aqueous solution, and tertiary amines are all effective catalysts. It is, therefore, imperative that the concentration of such contaminants be kept at a minimum when transporting or storing sizeable quantities of ethylene oxide Accdg to Hess Tilton (Ref 16), a 90% decompn takes place if 100% vapor of EtnO in a closed container is. initiated with MF. There is no upper limit of EtnO in air (the previously reported value of 80% was in error), but the lower expl limit is 3% (Ref 17, p 87)... 

The interpretation of the viscosity-temperature behavior of these complex systems is difficult since many aspects of the melt conditions must be simultaneously considered. These include the chemical composition of the melt to establish the nature of the polymeric network including the amphoteric behavior of species like AI2O3 and Fe2O3> as well as the acid/base behavior of mixed valence constituents such as iron oxides, and the formation of immiscible liquid phases sometimes associated with the existence of several types of stable anions of significantly different size or charge in the system the nature of the container since some of it may dissolve and affect the composition of the melt the existence of a solid phase to establish the effect on the composition of the residual liquid phase (the solid phase may not be the one expected from related phase equilibrium studies) the relative amount of the liquid and solid phases to establish the composition of the liquid phase (this composition changes as the solid crystallizes out of... 

In some cases it may be useful to reduce the catalyst activity level to facilitate the observation of early reaction steps. An example of this approach is shown by the two in situ studies illustrated in Fig. 28 [101]. When acetaldehyde-1,2- C was heated on a zeolite sample activated to 673 K, a complex product distribution was formed, which decomposed to CO, COj, and other products at higher temperatures. If a small amount of water was first adsorbed uniformly on the zeolite, acetaldehyde was converted almost quantitatively to crotonaldehyde by a similar in situ protocol. It seems that water levels the acidity of the zeolite in a manner analogous to that seen in nonaqueous acid-base chemistry. As an aside, note that the C chemical shifts of the carbonyl and 3 olefinic carbons are shifted downfield owing to the protonation equilibrium. This effect was discussed previously as a caveat to chemical shift interpretation. 

Temperature dependence equations for pK and pK values show the importance of good temperature control during pH meter calibration as well as in measurements. To a greater or lesser extent, all acid-base reactions vary with temperature. The effect of temperature changes for equilibrium reactions are closely described by the Valentiner-Lannung equation [80-82] ... 

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