SOLUBILITY OF RUBIDIUM OZONIDE IN LIQUID AMMONIA

A. B. Tsentsiper and M. S. Dobrolyubova UDC541.8+546.214+546.35+546.171.I

Since one of the methods of extract ing ozonides f rom ozonized hydroxides or hyperperoxides is to dissolve them inliquid ammonia, it is ve ry important to have data on solubility in the sys tem rubidium ozonide -- liquid ammonia. Hyperperoxides a re not ve ry soluble in liquid ammonia. According to Cohen and Margrave [1], in the range f rom --50 to --33 ~ only 0.006 :~ 0.002 g NaO2 dissolves in !00 cm 3 of am- monia. Hydroxides of alkali meta ls a re far more soluble in liquid ammonia; at --40 ~ 0.9 g RbOH dissolves in 100 ml of ammonia [2]. As r ega rds the a lkal i -meta l ozonides, only the solubility of KO 3 in liquid am- monia in the range f rom --35 to --80 ~ has been studied [3]. It was found that the sys tem KO3--NH 3 has a eutectic at --80 ~ Solomon et al. [4] state that the solubility of KO~ at --63 ~ is 12 g KOJl00 g NH~, which is approximately 1.5 t imes g rea te r than the value given by Malmrov and Sokovnin. Solomon et al. give the solu- bility of te t ramethylammonium ozonide in liquid ammonia as 1.3 g/100 g NI-I 3 at --63 ~

EXPERIMENTAL

The solubility of RbO 3 in liquid ammonia was studied in the apparatus shown in Fig. I. A vessel i with ~1.5 g of rubidium ozonide (97.8% RbO 3 and 2.370 RbO 2) was placed in a Dewar flask with acetone, cooled to the experimental temperature. About i0 ml of NH~, which had been twice distilled over Na to remove dis- solved water, was then condensed in i. The solution was shaken by shaking and by passing dry N 2 at inter- vals. A continuous feed of nitrogen led to considerable losses of NH3, which could disturb the equilibrium, particularly at higher temperatures.

Before a sample was taken, the sampling tube 2 was placed in the Dewar flask and the solution then pumped into it under pressure. When vessels 1 and 2 were connected by taps b and b', the excess solution was returned to vessel 1 from vessel 2. After a ~2 ml sample had been taken, vessel 2 was rapidly dis- connected from 1 at points a and a' and another sampling tube was connected. The ammonia was then driven over from the disconnected sampling tube to the receiver, where it condensed; dry nitrogen was passed through the sampling tube, stoppers inserted, and weighing performed. The condensed ammonia was evap- orated into a measured volume of a tit-rated H2SO 4 solution. In some experiments the sample was analyzed for the content of rubidium ozonide, rubidium hyperperoxide, and rubidium hydroxide.

During an experiment the temperature was kept constant by adding dry ice and, at low temperatures, liquid N2, the acetone being continuously stirred durhlg this process by a current of gaseous N~. The tem- perature was measured by a thermocouple 3, attached to the outer wall of vessel i.

Preliminary experiments on a specimen of RbO 3 containing 90.0% RbO3, 2.570 RbO2, and 7.0% RbOH had established that equilibrium is reached in approximately 2 h. Thus at --64 ~ the solution contained 7.8, 7.2, and 8.1 g RbO 3 per i00 g NH 3 aRer 2, 3, and 6 h, respectively; this is within the experimental accuracy (~5 rel. 70). Equilibrium was reached both from the low-temperature and the high-temperature side (no essential difference was observed). However, it is better to perform the experiments with falling tempera- tures. This guarantees the presence of an equilibrial solid phase, which is of great importance since the presence of a small amount of crystals is difficult to detect owing to the dark color of the solution.

The experimental data are given in Table i. Figure 2 shows the crystallization branch of RbO~. Below --84 ~ all the solution crystallized. In the crystallization range of NI-I 3 the RbO 3 content of the solu- tion changes markedly with the temperature; therefore, with the above-mentioned accuracy the determina- tion of RbO 3 solubility in the range from --77.8 to --83 ~ is undesirable. Therefore in Fig. 2 the NH 3 crys- tallization branch is shown as a dashed line. It will be seen that, as in the case of KO3, the system RbO 3- NH 3 (liquid) is of the simple eutectic type. The composition and temperature of the eutectic were deter- mined graphically (4.3 g RbO3/100 g NH 3 and --82 to --83 ~ respectively).

N. S. Kurnakov Institute of General and Inorganic Chemistry, Academy of Sciences of the USSR. Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2740-2742, December, 1967. Original article submitted April 7, 1967.

2607

\ $

Chamber Drying with dry crouton

b b'

2

.#

Fig. 1

r -50

-8O

-7O

-80

/ I I I 1 t t I I I I

I Z y ~ s 6 7 8 y IQ ~ g "RbOs/lO0 g NH3

-50

=80

-70

~0

Fig. 2

Fig. 1. Apparatus for determining the solubility of RbO 3 in liquid ammonia.

Fig. 2. Phase d iagram of the sys tem RbO 3 -- NI-I~ (liquid).

TABLE 1. Solubility of RbO 3 in Liquid NH 3

g RbO 3 per g Rbo s per .T., ~ 100gNH s T., ~ 100gNH s

.-48.0 10.5 --77.5 ] 5.6 --54.0 9.2 --81.0 [ 4.4 --60.0 7.3 --84.0 Only solid --63.0 6.7 I phase --70.5 6.3

As might be expected, es tabl ishment of equilibrium was accom- panied by growth of the crys ta ls ; f i rs t the smal l c rys ta ls dissolved and then, with decreasing tempera ture , the c rys ta ls grew and reached 1.5 mm in some cases . The composit ion of the equilibrial solid phase also changed and enr ichment with RbO 8 was observed. Thus, when the initial ozonide contained 90.0% RbO 3, 2.5% RbO2, and 7.0% RbOH its composition changed after separat ion of the solid phase f rom the solution with which it was in equilibrium at --64 ~ (the RbO 3 content fell to 97.3% and the RbOH content to 1.9%).

Therefore the pures t RbO3, free of hydroxide, can be obtained by slow washing with a re la t ive ly small port ion of liquid NH 3. However, if the ozonide/hydroxide ra t io in the initial substance is less than the ra t io of their solubilities, the equilibrial solid phase will be enriched with hydroxide and the solution with ozonide.

C O N C L U S I O N S

1. The authors studied the solubility of rubidium ozonide in liquid ammonia in the range --48 to --84 ~ The sys tem RbO 3 - NH 3 has a simple eutectic at --82 to --83 ~ The eutectic contains 4.0% RbO 3 (4.3 g RbO3/100 g NH3).

2. Depending on the RbO 3 and RbOH contents in the initial substance, in saturated solutions of NH 3 the solid phase will be enriched with either RbO 3 or RbOH.

i . 2. 3. 4.

L I T E R A T U R E C I T E D

S. H. Cohen and J. L. Margrave , J. Inorgan. Nuel. Chem., 1.~4, No. 3/4, 4301 (1960). G. P. Nikol 'skii , Z. A. Bagdasar 'yan , and I. A. Kazarnovskii , Dokl. AN SSSR, 7._~7, 69 (1951). S. Z. Makarov and E. I. Sokovkin, Dokl. AN SSSR, 137, 612 (1961). I. J . Solomon, A. J. Kacmarek, J. M. Me Donough, and K. Hattory, J. Amer. Chem. Soc., 82, 5640 (1960).

2608