A survey of reported compositions along the solubility curve and compositions of coexisting phases in equilibrium for the system nitromethane + acetic acid + water is given in Table 1.

Solubility curve The system nitromethane + acetic acid + water forms a miscibility gap of Type I, Treybal.⁴ Only one binary pair of components, nitromethane + water, is partially miscible. The data for this system were previously compiled and critically evaluated.⁵ The recommended values for the solubility of nitromethane in water at 293.2 K is x₁" = 0.0345; and at 313.2 K, x₁" = 0.0426. The solubility of nitromethane in water at 293.2 K reported in Maslovskaya and Zhuravlev² (0.0900 mass fraction; 0. 0284 mole fraction) and at 313.2 K in Maslovskaya³ (0.1000 mass fraction; 0.0318 mole fraction) are rejected because they are inconsistent with recommended values.⁵
Solubility data obtained by the titration method for the ternary system nitromethane + acetic acid + water were reported in three references. The data of Maslovskaya,³ which were reported at 313.2 K, indicate a smaller miscibility gap than the data at 293.2 K reported by Maslovskaya and Zhuravlev.² Thus, with increasing temperature the mutual solubility of the components increases, Fig. 4 . On the other hand, data on solubility, Maslovskaya and Zhuravlev,² at 293 K differ only slightly from the data Skrzec and Murphy,¹ reported at 300 K, Fig. 4. Therefore, the solubility data of Skrzec and Murphy¹ were poor and not were considered, but are given in Fig. 4 for comparison. Experimental errors were not reported in the papers, but are estimated by the evaluator to be ±0.002 mass fractions. Solubility data at 293.2 K and 313.2 K (water-rich and nitromethane-rich branches together) are described by an algebraic equation in the form:
x₂ = a + b· x₃ + c· ln(x₃) + d· (ln(x₃))² + e· (x₃)^1/2.
This smoothing equation gives a smaller standard deviation than any other tested equation. The equation parameters (a, b, c, d, e) were calculated by the least squares method and presented in Table 2. Binodal curves in this system were calculated and compared separately for solubility data reported in Maslovskaya and Zhuravlev² and Maslovskaya.³
The solubilities calculated by the proposed equation are presented in Fig. 4 and in Table 3. Experimental solubility data^1-3 are presented in Fig. 4 for comparison.

Liquid-liquid equilibrium (LLE) data

LLE data for the ternary system nitromethane + acetic acid + water were reported in Skrzec and Murphy¹ and Maslovskaya.³ Composition of each phase in Maslovskaya³ was calculated from the index of refraction-composition curve of saturated mixtures prepared at the time of saturation curve measurements. The tie lines at 313.2 K cover the whole range of the miscibility gap and are nearly parallel to one another and to the tie line between nitromethane and water, Fig. 4. The tie line data in Skrzec and Murphy¹ were obtained by the analytical method. Data reported at 293.2 K and at 313.2 K, Maslovskaya,³ and also at 299.9 K in Skrzec and Murphy,¹ are in agreement. Plait points were reported in all references and presented in Table 4. Experimental errors were not reported in the papers, but are estimated by the evaluator to be ±0.005 mass fractions.

Recommended or tentative data

Solubility and liquid-liquid equilibrium data measured by different methods are in agreement with one another. Experimental data on solubilities at T/K = 293.2 K and 313.2 K, Zhuravlev and Maslovskaya² and Maslovskaya,³ are presented in Fig. 4. The ternary solubility data, Zhuravlev and Maslovskaya² and Maslovskaya,³ were used to obtain equation parameters of the binodal curve. The experimental liquid-liquid equilibrium data at 293.2 K and 299.9 K, Skrzec and Murphy¹ and Maslovskaya,³ are used for construction of the smoothed curve for distribution of acid between nitromethane-rich and water-rich phases, Fig. 5 . These data also should be considered as tentative.
In view of the inaccurate results obtained in Zhuravlev and Maslovskaya² and Maslovskaya³ for the binary nitromethane + water system, the evaluator considers the ternary system data to be tentative and concludes that new studies on the ternary system would be of value.