Liquid Ammonia as Solvent

One of the most water-like and certainly one of the most comprehensively studied, of the non-aqueous solvents is liquid ammonia. Early interest in reactions in this medium has been continued until the literature has become extremely voluminous and complex. References already cited shuld be supplemented by the excellent yearly review compiled for the period 1933-1940 under the general guidance of Watt.

Solubility in Liquid Ammonia

Inasmuch as the solubilities of materials in liquid ammonia are often markedly different from the corresponding solubilities in water and inasmuch as the reaction solute undergo are often functions of their solubilities, a general summary of solubilities is desirable. Perhaps the outstanding difference between ammonia and water is the ability of ammonia to dissolve, without chemical reaction, five metals which are strongly reducing in character. Thus the alkali metals dissolve readily to yield characteristic blue solution from which the free metals can be recovered by evaporation of the solvent. The alkaline earth metal (calcium, strontium, and barium) shows similar behaviors, although their solubilities are not as large and evaporation of ammonia yields, as first solid phases, their unstable metal ammonates of composition M(NH3) 6 . Magnesium exhibits a slight, though measurable, solubility, as does aluminum, and the same is apparently true to lesser degree of beryllium, zinc, gallium, lanthanum, cerium and manganese.

Non metals such as iodine, sulfur, selenium and phosphorus are somewhat soluble in liquid ammonia. With sulfur, and perhaps with the other as well, this solubility is due, at least in part, to reaction with the solvent. The solubility of inorganic salts show trends markedly different from those noted in water. As might be expected, those salts which are most readily and extensively solvated are the most soluble. With ammonia the nature of the anion appear to play an even more important role than with water, the nature of the natural of the cation being comparatively unimportant except that a number of ammonium salts are soluble irrespective of anion. Among the halides solubility increses markedly from fluoride to iodide, essentially al fluorides being insoluble and even such iodides as that of silver being very soluble. The only chlorides which are really soluble are ammonium and beryllium chloride. Soluble inorganic salt ordinarily contain anions as iodide, perchlorate, nitrate, thiocyanate, cyanide, or nitrite, whereas salt containing carbonate, oxalate, sulfate, sulfite, sulfide, arsenate, phosphate, hydroxide, or oxide ions uniformly insoluble.


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