Action of Acids and Bases

The diagram shown above is based, in part, on Bell s compilation of pH-rate profiles. The interested reader will wish to consult his classic presentation as well as specific entries on the properties and actions of acids and bases throughout this Handbook. 

Carbenes were the earliest proposed Cl intermediates. These were considered to be generated via a-elimination of water from methanol itself [9,10], or from catalyst surface methoxyls [11]. The reaction may be assisted by cooperative action of acid and base sites on the catalyst [10]. Olefins would be formed by polymerization of the (free) CIl2. To overcome the high energetic requirements of carbene generation (vide infra), and the low probability of CH2 self-condensation, Chang and Silvestri [lb] proposed a concerted mechanism of carbene generation with sp3 insertion into the C-H bond of DME to form MeOEt. 

Lowry s theory, that the reactions occur under the combined action of acid and base, makes ka the constant for water acting as a base and... 

Action of Acids and Bases on Salts, and of Salts on each other. —If an acid be added to a solution of a salt whose acid it nearly equals in chemical activity, the salts of both acids and the free... 

Baekeland s success derived from the fact that he had managed to perfect a process which had been much studied after 1900. By careful control of the proportions of phenol and formaldehyde, and recognition of the catalytic action of acids and bases, he produced a homogenous product. 

Further predictions in 1875 Metal easily obtained by reduction. Will melt at quite a low temperature. Almost involatile. Not oxidized on contact with air. When heated to red-heat, should decompose water. The pure and fused metal will be only slowly subject to the action of acids and bases. 

Scheme (b) includes reactions formerly described by a variety of names, such as dissociation, neutralisation, hydrolysis and buffer action (see below). One acid-base pair may involve the solvent (in water H30+ —H2OorH20 — OH ), showing that ions such as HsO+ and OH- are in principle only particular examples of an extended class of acids and bases though, of course, they do occupy a particularly important place in practice. It follows that the properties of an acid or base may be greatly influenced by the nature of the solvent employed. 

Another definition of acids and bases is due to G. N. Lewis (1938). From the experimental point of view Lewis regarded all substances which exhibit typical acid-base properties (neutralisation, replacement, effect on indicators, catalysis), irrespective of their chemical nature and mode of action, as acids or bases. He related the properties of acids to the acceptance of electron pairs, and bases as donors of electron pairs, to form covalent bonds regardless of whether protons are involved. On the experimental side Lewis definition brings together a wide range of qualitative phenomena, e.g. solutions of BF3, BC13,... 

ACID-BASE DISSOCIATION EQUILIBRIA. STRENGTH OF ACIDS AND BASES The dissociation of an acid (or a base) is a reversible process to which the law of mass action can be applied. The dissociation of acetic acid, for example, yields hydrogen and acetate ions ... 

THE STABILITY OF COMPLEXES In the previous section hints were made about the differences in stabilities of various complexes. In order to be able to make more quantitative statements and comparisons, a suitable way has to be found to express the stability of complexes. The problem in many ways is similar to that of expressing the relative strength of acids and bases. This was done on the basis of their dissociation constants (cf. Section 1.16), obtained by applying the law of mass action to these dissociation equilibria. A similar principle can be applied for complexes. 

Section 19.1 discusses the Brpnsted theory of acids and bases, which extends the concepts of add and base beyond aqueous solutions and also explains the acidic or basic nature of solutions of most salts. Dissociation constants, the equilibrium constants for the reactions of weak acids or bases with water, are introduced in Section 19.2. The concept of the ionization of covalent compounds is extended to water itself in Section 19.3, which also covers pH, a scale of acidity and basicity. Section 19.4 describes buffer solutions, which resist change in their acidity or basicity even when some strong acid or base is added. Both the preparation and the action of buffer solutions are explained. Section 19.5 discusses the equilibria of acids containing more than one ionizable hydrogen atom per molecule. 

Berthollet reasoned that such an exchange of bases did not take place because the partition of acids and bases was in effect. When the exchange did occur, it was due not to the affinities in action, but to other real causes such as crystallization and precipitation. Chemists had inadvertently ascribed the strongest affinities to the substances that precipitated easily. Other causes, such as heat and efflorescence, also contributed to the outcome of complex affinities, as was the case for natron. In short, elective affinity involved an unsaturated substance, while complex affinities worked between saturated substances. The notion of elective affinity was tightly bound to the analytic procedure in which two acids, one combined in the salt and the other free, had to compete for the common base. 

The surface acid-base properties of bulk oxides can be conveniently investigated by studying the adsorption of suitably chosen basic-acidic probe molecules on the solid. Acidic and basic sites are often present simultaneously on solid surfaces. The two centers may work independently or in a concerted way, and the occurrence of bifunctional reaction pathways requiring a cooperative action of acidic and basic centers has also received considerable attention [39]. The acid-base properties of numerous amorphous metal oxides investigated by mrcrocalorime-try have been summarized in an extensive review by Cardona-Martinez and Dumesic [11]. 

Dissociation Constants of Acids and Bases.—If the law of mass action is applied to the equilibrium between an acid HA and the basic solvent S, i.e., to the equilibrium... 

JVIake, as in the preceding experiment, dilute solutions of sodium chloride (common salt), potassium nitrate, potassium sulphate, and barium chloride. Test each solution with litmus paper and describe the result. Compare with the action of acids and of bases on litmus paper. 

Salts Compounds formed by the union of acids and bases, by the action of alkalies upon metals, or by the direct union of elements. The term is often incorporated in the common name of salts used as pharmaceuticals bitter salts, epsom salt, or Seidlitz salt (magnesium sulfate), preparing salt (sodium stannate), Preston s salts (ammonium chloride), Rochelle salt or Seignette s salt (potassium and ammonium tartrate), salt of Mars (ferrous sulfate), salt of Saturn (lead acetate), salt of tartar (potassium carbonate), salt of tin (stannous chloride), salt of wisdom (mercury bichloride and ammonium chloride), sore-throat salt (fused potassium nitrate), vinegar salts (calcium acetate), and vomiting salt (zinc sulfate). The term is also applied to some acids, such as salt of lemon or sour salt (citric acid), salt of sorrel (oxalic acid), and spirit of salt (muriatic acid). ... 

In this chapter we have encountered the most important analytical aspects of acids and bases (a) their individual speciation, as described by the mass action law, and as reflected in the distribution and logarithmic concentration diagrams, (b) their buffer action, and (c) their neutralization, as exploited in acid-base titrations. 

The 2, 19-epoxydienone (372) has been prepared by the action of acid or base upon either the fluoro- or chloro-19-acetates (371), which were obtained by halogenation of the oxalyl derivative of (370) and subsequent cleavage of the 6/5,19-oxide ring with acetic anhydride-toluene-p-sulphonic acid. 

Electrocoating materials are acid oligomers RCOOH or more frequently R(C00H)jj for anodic deposition or RoN for cathodic deposition. These" oligomers are water insoluble but can be dispersed in water through the action of acids or bases, used as external solubilizers. The solubilization and deposition processes can be symbolized as follows ... 

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