CHEMISTRY

S. Z. MAKAROV and E. I. SOKOVNIN

ON THE SOLUBILITY OF POTASSIUM OZONIDE IN LIQUEFIED AMMONIA

SYSTEM $\mathrm{NH_3}$—$\mathrm{KO_3}$

(Presented by Academician I. I. Chernyaev, 12 XI 1960)

It is known from the literature that $\mathrm{KO_3}$, one of the representatives of the higher oxygen compounds—ozonides—is fairly readily soluble in liquefied ammonia. This property was used to isolate it from the products of ozonation of KOH ($^{1,2,4}$). However, the absence in the literature of quantitative data on the polythermal solubility of potassium ozonide in liquefied ammonia makes it impossible to obtain $\mathrm{KO_3}$ in its purest form and to isolate it as single crystals. In this connection, the literature contains no indications of a purity of $\mathrm{KO_3}$ higher than 93.3% ($^1$), and experimental data on the actual structure of $\mathrm{KO_3}$ are entirely lacking. Authors have had to confine themselves to comparison with the similar structure of potassium azide—$\mathrm{KN_3}$ ($^3$).

Taking all these circumstances into account, we undertook a study of the phase diagram of the system $\mathrm{NH_3}$—$\mathrm{KO_3}$. In the region of $\mathrm{KO_3}$ crystallization (see Fig. 1), the data were obtained on the basis of the isothermal solubility of potassium ozonide in liquid ammonia at temperatures of $-35$, $-45$, $-55$, $-65$, and $-75^\circ\mathrm{C}$. In the region of $\mathrm{NH_3}$ crystallization, the investigation was carried out by the well-known visual-polythermal method.

The data, corresponding to the average results of three to four measurements in the temperature interval from $-33$ to $-80^\circ$, i.e., in the region of existence of liquid ammonia in this system at ordinary pressure, are summarized in Table 1 and in the diagram $\mathrm{NH_3}$—$\mathrm{KO_3}$ (Fig. 1).

Table 1

Solubility data for potassium ozonide in liquid ammonia

* Composition established graphically.

The diagram obtained by us belongs to the simplest type of eutectic diagrams, with a eutectic composition of about $5.1\ \mathrm{g}\ \mathrm{KO_3}/100\ \mathrm{g}\ \mathrm{NH_3}$ at a temperature of $-80^\circ$.

An increase in temperature leads to an increase in the solubility of potassium ozonide in liquefied ammonia with $K = 0.22\ \mathrm{g}\ \mathrm{KO_3}$ per $1^\circ$ and near the tempera-

the boiling temperature of the latter reaches its limiting value. According to the data obtained, at (-35^\circ) the solubility was found to be about 15 g (\mathrm{KO_3}/100) g (\mathrm{NH_3}). The lowering of the freezing (melting) temperature of ammonia in this system correspondingly varies from (-77.7) to (-80^\circ).

The availability of the data obtained for the (\mathrm{NH_3})—(\mathrm{KO_3}) system makes it possible, on the one hand, to obtain (\mathrm{KO_3}) in its purest form by the method of polythermal crystallization (region (ED)), and, on the other hand, to concentrate dilute ozonide solutions obtained after extraction

Fig. 1

of it from ozonized alkali by the freezing-out method (region (AE)). The use of polythermal crystallization enabled us comparatively easily to obtain individual samples of potassium ozonide with a (\mathrm{KO_3}) content of (98.1\%) by weight.

In studying the system, ammonia of high purity was used, prepared by triple distillation of liquid ammonia and drying with metallic sodium. Potassium ozonide was freed by preliminary recrystallization from the ordinarily present (\mathrm{KOH \cdot H_2O}) (1), and thus its influence in the system was reduced to a minimum. The data obtained, in addition to being of known scientific interest, may have substantial importance for the technology of obtaining potassium ozonide.

The experimental part will be set forth in greater detail in a special article.

Institute of General and Inorganic Chemistry
named after N. S. Kurnakov
Academy of Sciences of the USSR

Received
9 XI 1960

REFERENCES

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4. S. Z. Makarov, E. I. Sokovnin, DAN, 135, No. 3, 606 (1960).