Metal-Ammonia Solutions

Abstract

A SOLUTION of sodium in liquid ammonia is known¹ to give a eutectic, m.p.-110° C. We have now determined the melting points for the eutectic of potassium, ˜?157° C.; of lithium, ˜-185° C., and of calcium, ˜-90° C. The solids separating from the frozen eutectic solutions of potassium and sodium are undoubtedly ammonia and the metal ; the latter can be seen as silvery crystals. From frozen calcium solutions a brass-like solid separates, which certainly contains the hexammoniate known to be stable even at room temperature². From the lithium solution a similar solid is obtained, and it therefore seems probable that it also forms an ammoniate. A resemblance between calcium and lithium can also be found in the short time (small amount of heat) required in both cases to melt the eutectic compared with that for sodium or potassium. This is understandable if one remarks that the heat taken up in the process goes chiefly in melting ammonia (which has a very high latent heat), since this, in the ammoniates, is already associated to some extent with the metal, and very little extra is required to form the eutectic solution. The resemblance extends to chemical reactions, since a concentrated solution of lithium in ammonia, which is stable and has a very low vapour pressure at room temperature, can be used to hydrogenate benzene rings, and exerts some demethylating effect on methoxyalkylbenzenes (compare calcium hexammoniate)³.