Reactions in Liquid Ammonia-I Ammonolysis of Hexavalent Chromium Derivatives

Abstract

Although recent researches have served to clarify, to a great extent, the chemistry of the aquo ammono sulfuric acids (1) and older researches to a somewhat lesser extent the chemistry of the aquo ammono phosphoric acids (2), the literature concerning the corresponding compounds of other acidforming elements of periodic groups five and six remains incomplete, and, in many cases, contradictory. This uncertainty is particularly true of the ammono derivatives of hexavalent chromium. In spite of a number of publications concerning the ammonolysis of various hexavalent chromium derivatives, there still has not been forthcoming a definite answer to the question, Are aquo ammono chromic acids obtainable by direct reaction of hexavalent chromium compounds with anhydrous ammonia? Several workers during the past seventy-five years have reported the preparation of salts of amidochromic and imidodichromic acids, (3, 4, 5) but several of their contemporaries (6, 7, 8) were unable to repeat their results. Since many of these early experiments involved ammonolytic reactions, followed by treatment of the ammonolytic product with water, it is almost certain that any ammono derivatives which might have formed were immediately hydrolyzed. Rosenheim and Jacobsohn later reported the preparation of ammonium imidochromate, (NH4) CrO3NH, along with some chromic oxide by the reaction of chromic anhydride with liquid ammonia in a sealed tube at room temperature (9). The analytical results reported, however, did not agree very well with the formula given. The author hoped, in starting this problem, to be able to clarify somewhat the ambiguity in connection with the ammonolysis of hexavalent chromium compounds and to determine whether or not such reactions may be used for the preparation of aquo ammono chromates. It was decided, therefore, to study the reactions of chromic anhydride and of potassium chlorochromate with liquid ammonia under highly anhydrous conditions. Similar reactions had resulted in the formation of aquo ammono sulfates (1). The high oxidation potentials of these chromium compounds, however, caused complications, as is shown by succeeding data. A series of reactions of chromic anhydride with an excess of anhydrous ammonia was carried out at -33?. On analyzing the ammonolytic product, it was found in every case that about one-fourth of the total chromium had been reduced to the trivalent state. When treated with liquid ammonia in a sealed tube at 0? under anhydrous conditions, chromic anhydride reacts so vigorously that, in some cases, at least, the reaction mixture inflames under the liquid ammonia. The presence of bright green particles, interspersed through the brown ammonolytic product, indicates considerable reduction.