Acidities of Ammonium Ions

The ammonium ion is the conjugate acid of the weak base, ammonia, and hence expected to be moderately acidic (relative to water). Accordingly, the equation below explains the observed acidity of ammonium ions. 

Indeed there isn t, and it takes a look at matters in the gas phase to straighten things out. In the gas phase, the trend is regular. The basicity of amines increases with substitution, and the acidity of ammonium ions decreases wth substitution (Fig. 6.45). 

The acidities of benzoic acid and of acetic acid differ by a factor of about 4, whereas the acidities of the anilinium ion and of the methylammonium ion differ by about a factor of lO . Why does the aromatic ring have so little effect on the acidity of carboxylic acids and a large eflFect on the acidity of ammonium ions ... 

By the evolution of ammonia with Devarda s alloy in alkaline solution in absence of ammonium ions this is used quantitatively, the ammonia being absorbed in excess standard acid and the excess acid back-titrated. 

Note that the concentration of H2O is omitted from the expression because its value is so large that it is unaffected by the dissociation reaction.The magnitude of provides information about the relative strength of a weak acid, with a smaller corresponding to a weaker acid. The ammonium ion, for example, with a Ka of 5.70 X 10 °, is a weaker acid than acetic acid. 

Ammonium Ion Removal. A fixed-bed molecular-sieve ion-exchange process has been commercialized for the removal of ammonium ions from secondary wastewater treatment effluents. This application takes advantage of the superior selectivity of molecular-sieve ion exchangers for ammonium ions. The first plants employed clinoptilolite as a potentially low cost material because of its availability in natural deposits. The bed is regenerated with a lime-salt solution that can be reused after the ammonia is removed by pH adjustment and air stripping. The ammonia is subsequentiy removed from the air stream by acid scmbbing. 

Cadmium Hydroxide. Cd(OH)2 [21041-95-2] is best prepared by addition of cadmium nitrate solution to a boiling solution of sodium or potassium hydroxide. The crystals adopt the layered stmcture of Cdl2 there is contact between hydroxide ions of adjacent layers. Cd(OH)2 can be dehydrated to the oxide by gende heating to 200°C it absorbs CO2 from the air forming the basic carbonate. It is soluble ia dilute acids and solutions of ammonium ions, ferric chloride, alkah haUdes, cyanides, and thiocyanates forming complex ions. 

The previous calculation assumed that the solvation energy of ammonium was equal the solvation energy of a single water molecule times the number of water binding sites. Is this a valid assumption Compare the electrostatic potential maps of ammonium ion and ammonium ion+water. For which are the exposed hydrogens more acidic Did the calculation underestimate or overestimate the difference in solvation energies ... 

These equations say that the Kh of an amine multiplied by the of the corresponding ammonium ion is equal to Kw, the ion-product constant for water (1.00 x 10 14). Thus, if we know Ka for an ammonium ion, we also know for the corresponding amine base because /stronger base has an ammonium ion with a larger p... 

In practice, one proceeds as follows. The value of bh >s determined for the reaction with a series of acids of similar structure, that is, for carboxylic acids or ammonium ions, etc. Limiting the data to a single catalyst type improves the fit. since the inclusion of data for a second ype of acid catalyst might define a close but not identical line. This means that Ga may be somewhat different for each catalyst type. A plot of log(kBH/p) versus log(A BH(7//i) is then constructed. This procedure most often results in a straight line, within the usual —10-15 percent precision found for LFERs. One straightforward example is provided by the acid-catalyzed dehydration of acetaldehyde hydrate,... 

While their physiologic role is uncertain, L-amino acid oxidases of liver and kidney convert amino acids to an a-imino acid that decomposes to an a-keto acid with release of ammonium ion (Figure 29-6). The reduced flavin is reoxidized by molecular oxygen, forming hy-... 

The conjugate acids of ammonia and methylamine are the ammonium ion, NH44" (pKa = 9.2) and the methylammonium ion, CH3NH3+ (pKa = 10.6) respectively. Since methylammonium ion is a weaker acid than ammonium ion, methylamine is a stronger base than ammonia. 

Excess nitrogen is eliminated from the body in the urine. The kidney adds small quantities of ammonium ion to the urine in part to regulate acid-base balance, but nitrogen is also eliminated in this process. Most excess nitrogen is converted to urea in the liver and goes through the blood to the kidney, where it is eliminated in urine. 

Amino groups released by deamination reactions form ammonium ion (NH " ), which must not escape into the peripheral blood. An elevated concentration of ammonium ion in the blood, hyperammonemia, has toxic effects in the brain (cerebral edema, convulsions, coma, and death). Most tissues add excess nitrogen to the blood as glutamine. Muscle sends nitrogen to the liver as alanine and smaller quantities of other amino acids, in addition to glutamine. Figure I-17-1 summarizes the flow of nitrogen from tissues to either the liver or kidney for excretion. The reactions catalyzed by four major enzymes or classes of enzymes involved in this process are summarized in Table T17-1. 

Acrylic acid and ammonium ions (Abdelmagid and Tabatabai, 1982 Brown and Rhead, 1979 Kollig, 1993) were reported as hydrolysis products. The hydrolysis rate constant at pH 7 and hydrolysis half-lives are reduced significantly at varying pHs and temperature. At 88.0 °C and pH values of 2.99 and 7.04, the half-lives were 2.3 and 6.0 d, respectively (Ellington et al., 1986). Decomposes between 175 and 300 °C (NIOSH, 1994). 

Chemical/Physical. Kanno et al. (1982) studied the aqueous reaction of benzene and other aromatic hydrocarbons (toluene, xylene, and naphthalene) with hypochlorous acid in the presence of ammonium ion. They reported that the aromatic ring was not chlorinated as expected (forming chlorobenzene) but was cleaved by chloramine forming cyanogen chloride (Kanno et al, 1982). 

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