Ammonium-amalgam

In Franklin s system, for example, the analogs of the oxygen acids are the amides containing —NH2 groups where —OH groups existed in the acid. Such amides, as a rule, can be made by action of ammonia on acid chlorides (Chap. 14). The relationships between the three types of compounds are illustrated in Table 15-3. 

Oxygen Acids, Their Acid Chlorides, and Amides 

The acid amides, on treatment with hot aqueous acid or base, are hydrolyzed to their parent acids or to the anions of these acids. 

Of some interest is the electrolysis of ammonium salts with a mercury cathode. The mercury cathode then contains what may be regarded as 

The more common ammonium salts need not be described here. It should be recalled that all such salts decompose at temperatures below 350 degrees, often into ammonia and the parent acid. Thus, ammonium salts may be removed from most metal salts by vigorous heating. 

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Although the properties of metal amalgams and intermetallic compounds in mercury have been investigating for many years and are already well recognized, the nature of ammonium amalgam, as well as quaternary ammonium amalgams, still remains a subject of controversy. 

Ammonium amalgam was first reported in 1805 by Seebeck, who electrolyzed ammonium carbonate solution at mercury cathode. A concise review of the concepts on the structure of ammonium amalgam is given, for example, in Ref. 200. 

The studies on composition and instability of ammonium amalgam were continued later by the same group of researchers [204, 205]. 

Baranski and Lu [209] have carried out, applying microelectrodes, voltammetric studies on ammonium amalgam in propylene carbonate solutions at room temperatures. The sweep rates up to 80 V s were appropriate for the analysis of the formation kinetics of this compound. Experimental and numerical simulation results have shown that ammonium amalgam was formed via fast charge-transfer process and its first-order decomposition was characterized by the rate constant of about 0.6 s . Diffusion coefficient of NH4 radical in mercury was estimated to be about 1.8 X 10 cm s k The formal potential of NH4+ (aq)/NH4(Hg) couple was determined as—1.723 V (SHE). 

Kovaleva and Gladyshev [210] have proposed classification of hydrogen-containing amalgams. Ammonium amalgam (NH4 ) Hg has been included in... 

Krasensky and Studnickova [221] have prepared quaternary ammonium amalgam via electroreduction of tetraethylam-monium tetrafluoroborate in the aqueous medium at the room temperature. At the applied voltage of —2.8 to —2.4 V versus sodium saturated calomel electrode (SSCE) hydrogen evolution occurred simultaneously. Composition of the black precipitate formed was found to be Et4N Hg, where x = 2.9 0.8. 

To conclude, it should be said that in spite of numerous studies, the structure of ammonium amalgams has not yet been unequivocally established. 

In extending our study of chemical kinetics, we sought systems as far removed as possible from ordinary aqueous and organic solutions. The decomposition of ammonium amalgam... 

The facts are readily explained on the theory that decomposition of the ammonium amalgam occurs very slowly as an homogeneous reaction at temperatures below zero and that a rapid, heterogeneous reaction takes place at the surface of little droplets of liquid ammonia which are dispersed throughout the mercury. The surface tension of the mercury is sufficient to cause liquefaction of the first ammonia which is liberated. The autocatalytic effect occurs when the reaction has had time to build up these droplets of liquid ammonia. 

Ammonium amalgams are Zintl phase salts with mercury anions [iii-iv]. 

III.38 AMMONIUM ION, NH4 (Mt 18 038) Ammonium ions are derived from ammonia, NH3, and the hydrogen ion H+. The characteristics of these ions are similar to those of alkali metal ions. By electrolysis with a mercury cathode, ammonium amalgam can be prepared, which has similar properties to the amalgams of sodium or potassium. 

As mentioned on p. 1, ammonia combines with acids to form salts analogous to the metallic salts, most of them being isomorphous with the corresponding salts of potassium, and very similar to them. In these salts the univalent radical ammonium, NH4, functions as a metal. It has never been isolated, but its metallic character is displayed in the formation of an ammonium-amalgam (p. 211) resembling the amalgams of sodium and potassium. 

The formation of an ammonium-amalgam, the general character of the ammonium salts, the existence of the monohydrate, the electrochemical properties of aqueous solutions of ammonia, and the similarity of the quaternary ammonium bases to the hydroxides of sodium and potassium, justify the consideration of the ammonium compounds in conjunction with those of the alkali-metals. 

History.—The name ammonium is assigned to the radical NH4, supposed to be present in the so-called ammonium-amalgam. This substance was first prepared by Sebeck by electrolyzing ammonium salts in contact with mercury, and later by Berzelius and Pontin. Ampere regarded ammonia as the oxide of a metallic-like substance related to the alkalies.2... 

Ammonium Amalgam. The similarity of the ammonium ion to an alkali ion suggests that it might be possible to reduce ammonium ion to ammonium metal, NH. This has not been accomplished however, a solution of ammonium metal in mercury, ammonium amalgam, can be made by cathodic reduction of ammonium ion. 

Liquid ammonia as solvent sodium amide ammonium amalgam hydrazine hydroxylamine. 

Describe laboratory methods of preparing a) ammonia, b) nitrous oxide, c) nitric oxide, d) nitrogen trioxide, e) nitrogen dioxide, f) nitric acid, g) sodium nitrite, h) hydrazine, i) ammonium amalgam. 

The reduction of benzothiophene by ammonium amalgams is discussed in Chapter 28. 

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