Ammonia acidity constant

It is therefore apparent that dissociation constants may only be compared in the same solvent. Ammonia is a stronger donor than water, but liquid ammonia has a much lower dielectric constant than the latter. The acidity constant of hydrochloric acid in liquid ammonia is much lower than in water, in which it is completely ionized and completely dissociated, whereas the complete ionization in liquid ammonia is not followed by extensive ionic dissociation due to its low dielectric constant. On the other hand, the acidity constant of acetic acid is somewhat higher in liquid ammonia than in water since in the latter if Ion is much lower than in liquid ammonia, in which complete ionization is achieved. 

The bond dissociation energy (BDE) and acidity constant (p ) of cubane (Cub—H) have been determined experimentally by Eaton and co-workers (Hare, M. Emrick, T. Eaton, P. E. Kass, S. R, J. Am. Chem. Soc., 1997, 119, 237-238). The BDE is unusually high for a tertiary C—H bond, 427 kJ/mol, about 25 kJ/mol higher than in isobutane. The C—H bond is also quite acidic, comparable to the acidity of the N—H bond in ammonia, pK = 36, indicating an unusual stability for the anion... 

Although ammonia is constantly produced in the tissues, it is present at very low levels in blood. This is due both to the rapid removal of blood ammonia by the liver, and the fact that many tissues, particularly muscle, release amino acid nitrogen in the form of glulamhe or alanine, rather than as free ammonia (see Figure 19.13). 

Although liquid ammonia is known to have considerably stronger coordinating properties than water, the acidity constant of HCl is much smaller in liquid ammonia (K x 10" ) than in water 10 ). Ionization of HCl is essentially complete in both solvents, hence the observed large differences in dissociation constants are mainly due to differences in dielectric constants of the media (water, e = 81 ammonia, e = 17). 

On the other hand, the acidity constant of acetic acid is higher in liquid ammonia (K x 10 ) than in water (A 10 ). Acetic acid is moderately ionized in water, but in liquid ammonia, owing to its... 

There are some systems for which ambiguities arise in defining a dissociation constant, independently of the methods used for determining it. One of the long-standing problems of this kind concerns ammonia and the amines. The usual expression for the acid constant is = [NHf] [H30 ]/[NH4 ], where [NH ] denotes the total concentration of unionized ammonia in the solution. It has commonly been supposed that ammonia exists in aqueous solution partly as the molecule NH3 and partly as ammonium hydroxide NH4OH, so that as usually defined is more properly written... 

A more detailed understanding of the conjugate-base mechanism for the hydrolysis of kinetically inert amine complexes of cobalt(III) and rhodium(III) is possible if liquid ammonia is used as a solvent. Such techniques allow the separation of parameters for the pre-equilibrium step ( Tcb) and the rate-determining step. A polyamine complex generally contains more than one potentially acidic proton and each proton is characterized by its own acidity constant (Kcb)- exchange rates for... 

The dissociation constant of ethanoic (acetic) acid in liquid ammonia is greater than it is in water. Suggest a reason for the difference. 

Preparation of silver maleate. Dissolve 65 g. of pure maleic acid (Section 111,143) in the calculated quantity of carefully standardised 3-5N aqueous ammonia solution in a 1-htre beaker and add, whilst stirring mechanically, a solution of 204 g. of silver nitrate in 200 ml. of water. Filter oflf the precipitated silver maleate at the pump, wash it with distilled water, and press well with the back of a large flat glass stopper. Dry in an electric oven at 50-60° to constant weight. The yield of the dry silver salt is 150 g. Store in a vacuum desiccator in the dark. 

Sulphonamides. Mix together 1 0 g. of the dry acid or 1 - 2 g. of the anhydrous salt with 2 5 g. of phosphorus pentachloride f and heat under a reflux condenser in an oil bath at 150° for 30 minutes. Cool the mixture, add 20 ml. of dry benzene, warm on a steam bath and stir the solid mass well to extract the sulphonyl chloride filter. Add the benzene solution slowly and with stirring to 10 ml. of concentrated ammonia solution. If the sulphonamide precipitates, separate it by filtration if no solid is obtained, evaporate the benzene on a steam bath. Wash the sulphonamide with a little cold water, and recrystallise from water, aqueous ethanol or ethanol to constant m.p. 

Unsubstituted Amides. The most widely used synthetic route for primary amides is the reaction of fatty acid with anhydrous ammonia (11). Fatty acid and ammonia are allowed to react at approximately 200°C for 10 to 12 h under a constant vent of excess ammonia and water by-product. A pressure of 345—690 kPa (50—100 psi) is maintained by the addition of ammonia while the venting of water faciUtates the completion of the reaction. 

Dry air is blown through the solution to remove the excess of ammonia, and the solution is then dissolved in its own volume of absolute alcohol. A sample of this solution is titrated with standard oxalic acid, litmus being used as an outside indicator (Note 3). The amount of oxalic acid (Note 4) necessary to form the acid salt is placed in a large evaporating dish and dissolved in 4 1. of 95 per cent alcohol. The amine solution is then slowly run into the acid with constant stirring. During the addition of the last half of the amine solution, the container must be cooled in order to avoid the formation of the neutral oxalate,... 

The ethereal solution of crude quinidine and cinchonidine, obtained as described under cinchonine, is shaken with dilute hydrochloric acid, the excess acid neutralised with ammonia and sodium potassium tartrate added. The base is recovered from the precipitated tartrate by dissolving the latter in dilute acid and pouring the filtered solution in a thin stream, slowly and with constant stirring, into excess of ammonia solution. The crude alkaloid is converted into the neutral sulphate, and this recrystallised... 

After evaporation of the solvent, the solid residue consists of 5-(2-chlorobenzyl)-thieno[3,2-cl -pyridinium chloride which melts at 166°C (derivative n°30). This compound is taken up into a solution comprising ethanol (300 ml) and water (100 ml). Sodium borohydride (NaBH4) (20 g) is added portionwise to the solution maintained at room temperature. The reaction medium is maintained under constant stirring during 1 2 hours and is then evaporated. The residue is taken up into water and made acidic with concentrated hydrochloric acid to destroy the excess reducing agent. The mixture is then made alkaline with ammonia and extracted with ether. The ether solution is washed with water, dried and evaporated. The oily residue is dissolved in isopropanol (50 ml) and hydrochloric acid in ethanol solution is then added thereto. 

Note. All values are with reference to the molarity scale. Data for bases are expressed as acidic ionisation constants e.g. for ammonia we quote pK at =9 245 for the ammonium ion... 

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