Acid-base equilibria with salts

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). 

The decomposition of ADN can follow at least two different routes. One involves the formation, at 127°C, of ammonium nitrate and N20 [10], followed by a second step, with onset above 200°C, in which the AN decomposes to N02 and water. Potassium dinitramide decomposes with an analogous initial step, forming KNO3. A second route for ADN begins with dissociation of the salt into ammonia and dinitraminic acid, HN(N02)2. This can be viewed as an acid/base equilibrium ... 

Electrolytes (Na, K, Ca, Mg) and blood sugar must be carefully monitored, and any deviation from the norm should be corrected immediately. The risk of hypophos-phataemia must be eliminated by early parenteral substitution. During refractory episodes, such as those involving the acid-base equilibrium and hyperhydration, haemodialysis is usually indicated. In hypoalbumin-aemia, substitution with salt-free albumin is necessary. With about 75% of patients, artificial respiration is called for, the aim being controlled hyperventilation. 

Bott (1985) reported, however, an observation that strongly indicates the presence of the deprotonated form of the alkenediazonium salt 5.30. If this salt is kept with 0.05 equiv. OCDs K" for 20 h in the perdeuterated solvent mixture (CD3)2SO - CD3OD (5 2), almost complete exchange of the a-H for D is observed, but no nitrogen is evolved. It is likely that this exchange represents an acid-base equilibrium (5-7). The conjugate base 5.31 of this reaction is structurally related to the enol 5.25 with (at least) partial cumulative double bonds at the C(a)-atom ... 

The concepts of an acid, a base, and a salt are ancient ones that modern chemical science has adopted and refined. Our treatment of the subject at this stage will be mainly qualitative, emphasizing the definitions and fundamental ideas associated with acids and bases. The quantitative treatment of acid-base equilibrium systems is treated in another unit. 

C. Concentrations were in moles per 1000 g of liquid HF, i.e., molalities. The specific conductance L was derived from Lmeasured l-soivent- According to these authors, this expression did not represent the actual relationship because of interaction between the solvent and solute. A large part of the solvent conductance was attributed to traces of water and salts. Water was described as a strong electrolyte in liquid hydrogen fluoride, and also as a strong base therefore, it will interfere with the acid-base equilibrium under examination. 

Aldonic acids exist m equilibrium with their five or six membered lactones They can be isolated as carboxylate salts of their open chain forms on treatment with base... 

If the rate equation contains the concentration of a species involved in a preequilibrium step (often an acid-base species), then this concentration may be a function of ionic strength via the ionic strength dependence of the equilibrium constant controlling the concentration. Therefore, the rate constant may vary with ionic strength through this dependence this is called a secondary salt effect. This effect is an artifact in a sense, because its source is independent of the rate process, and it can be completely accounted for by evaluating the rate constant on the basis of the actual species concentration, calculated by means of the equilibrium constant appropriate to the ionic strength in the rate study. 

In this solvent the reaction is catalyzed by small amounts of trimethyl-amine and especially pyridine (cf. 9). The same effect occurs in the reaction of iV -methylaniline with 2-iV -methylanilino-4,6-dichloro-s-triazine. In benzene solution, the amine hydrochloride is so insoluble that the reaction could be followed by recovery. of the salt. However, this precluded study mider Bitter and Zollinger s conditions of catalysis by strong mineral acids in the sense of Banks (acid-base pre-equilibrium in solution). Instead, a new catalytic effect was revealed when the influence of organic acids was tested. This was assumed to depend on the bifunctional character of these catalysts, which act as both a proton donor and an acceptor in the transition state. In striking agreement with this conclusion, a-pyridone is very reactive and o-nitrophenol is not. Furthermore, since neither y-pyridone nor -nitrophenol are active, the structure of the catalyst must meet the conformational requirements for a cyclic transition state. Probably a concerted process involving structure 10 in the rate-determining step... 

An aqueous solution of a soluble salt contains cations and anions. These ions often have acid-base properties. Anions that are conjugate bases of weak acids make a solution basic. For example, sodium fluoride dissolves in water to give Na, F, and H2 O as major species. The fluoride anion is the conjugate base of the weak acid HF. This anion establishes a proton transfer equilibrium with water ... 

---