Vol. 2, No. 4,.4ugust, 1963
COBALT AND NICKEL ACETATES IN ACETIC ACID 823 CONTRIBUTION FROM THE DEPARTMENT OF CHEMISTRY, OF KANSAS, LAWRENCE, KANSAS UNIVERSITY
Cobalt and Nickel Acetates in Anhydrous Acetic Acid BY W. P. TAPPMEYER'
AND
ARTHUR W. DAVIDSON
Received December 31, 1962 Both cobalt and nickel acetates form hemisolvates with acetic acid. Both of these compounds exhibit retrograde solubility in anhydrous acetic acid between 16 and 65', solubility equilibrium being attained very slowly. From ternary mixtures of cobalt acetate, ammonium acetate, and acetic acid a t 30°, the solvated double salt NHICZH~OZ.~CO( CZH~OZ)~. HC2H302 has been isolated. The course of freezing point depression curves, as well as the composition of the solvates, suggests that these acetates exist mainly as dimeric species in their acetic acid solutions.
Introduction Fantastically conflicting statements concerning the solubilities of the acetates of cobalt and nickel in anhydrous acetic acid are to be found in the literature. Thus, whereas Spath2reported both of these compounds to be readily soluble in acetic acid, other German workers3 gave figures of 0.0381 N (0.11 mole yo)and 0.107 N (0.30 mole %) for the concentrations a t 25' of saturated solutions of the cobalt and the nickel salt, respectively. In later studies in this Laboratory, apparently saturated solutions containing a t 30' as much as 2.3 mole % of cobalt acetate4or 13 mole % of nickel acetate5 were obtained. It is significant that in most of these cases, as well as in a very recent study of cobaltous acetate in acetic acidJ6the authors reported their inability to obtain completely clear solutions, mentioning a slight insoluble residue, apparently quite unresponsive to changes in temperature, which was variously characterized as a "silky turbidity" or a "powdery sludge." The present study was undertaken in the hope that, with the identification of these residues, an explanation might be found for the apparently anomalous solubility behavior. In view of the previously observed formation of a ternary addition compound in the systems ammonium acetate-cupric or zinc acetate-acetic acid,7 i t seemed of interest also to determine the effect of ammonium acetate on the solubility of cobalt acetate. Experimental Methods Preparation of Materials.-Anhydrous acetic acid (m.p. 16.55-16.60') was prepared by adding the calculated amount of acetic anhydride to reagent grade (99.8%) glacial acetic acid, refluxing for 20 hr., and distilling. Anhydrous cobalt(I1) acetate was prepared by heating reagent grade tetrahydrate for 2 hr. a t 156". Anhydrous nickel acetate was prepared by heating reagent grade tetrahydrate for 8 hr. at 165". A saturated ammonium acetate solution was prepared by passing pure dry ammonia gas over anhydrous acetic acid in a desiccator until crystallization occurred. (1) Department of Chemical Engineering and Chemistry, University of Missouri, Missouri School of Mines and Metallurgy, Rolla, Mo. (2) Spath, Monatsh., 39, 235 (1912). (3) C. Schall and C. Thieme-Wiedtmarckter, 2. Elektrochem., 36, 337 (1929). (4) R. R . Spiegelhalter, M.S. Thesis, University of Kansas, 1950. (5) A. W. Davidson and W. Chappell, J. Am. Chem. SOC.,55, 3531 (1933). (6) P . J. Proll, L. H. Sutcliffe, and J. Walkley, J. Phys. Chem., 65, 455 (1961). (7) (a) A. W. Davidson and E. Oriswold, J . A m . Chem. SOC.,53, 1340 (1931): (b) ibid., 67, 423 (1935).
Equilibrium Data.-All solubility data were determined by the analytical method. Ground-glass stoppered tubes containing solution and excess solid were agitated from 1 to 4 days a t a fixed temperature, the mixture was filtered through a sintered glass filter, and the filtrate was analyzed as described below. The solid phase was dried between porous tiles in a desiccator over a solution of the same composition as that from which it had separated, and analyzed by the same method. Cobalt was determined by precipitation as the l-nitroso-2naphthol complex, followed by filtration, ashing, and conversion to the anhydrous sulfate. Nickel was determined by precipitation with dimethylglyoxime. For the determination of ammonium, the solution was made alkaline with sodium hydroxide solution, the liberated ammonia was distilled into a measured volume of standard hydrochloric acid, and the excess acid was titrated with sodium hydroxide solution. Freezing point depression data for cobalt acetate solutioi were obtained by means of a Beckmann differential thermometer,
Results Cobalt Acetate-Acetic Acid.-Dilute solutions (
