POLYTHERMAL SOLUBILITY OF THE NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O SYSTEM

ABSTRACT

The solubility of a system containing sodium chlorate, monoethanolammonium sulfate and water was studied using a visual-polythermal method in order to obtain a new composition of a defoliant for cotton. Based on the solubility polytherms of binary systems and internal sections, a polythermal solubility diagram of the NaClO₃–H₂SO₄ NH₂C₂H₄OH–H₂O system was constructed in the temperature range from -18.5 to -38°C. On the solubility phase diagram delineates the crystallization fields of ice, NaClO3, H₂SO₄ NH₂C₂H₄OH and a compound of the composition Na₂SO₄ NH₂C₂H₄OH, which was identified by chemical analysis methods. As a result of the study, it was established that the system under study belongs to the complex eutonic type.

АННОТАЦИЯ

Визуально-политермическим методом исследована растворимость системы, содержащая хлорат натрия, сульфат моноэтаноламмония и воды, с целью получения нового состава дефолианта для хлопка. На основе политерм растворимости бинарных систем и внутренних разрезов построена политермическая диаграмма растворимости системы NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O в интервале температур от -18.5 до -38°С. На фазовой диаграмме растворимости разграничены поля кристаллизации льда, NaClO₃, H₂SO₄·NH₂C₂H₄OH и соединения состава Na₂SO₄·NH₂C₂H₄OH, который идентифицирован химическими методами анализа. В результате исследования установлено, что изучаемая система относится к сложному эвтоническому типу.

Keywords: solubility, system, polytherm, diagram, concentration, defoliants.

Ключевые слова: растворимость, система, политерма, диаграмма, концентрация, дефолианты.

Introduction

In Uzbekistan, one of the most important branches of agriculture is cotton growing. When chemically affecting cotton to remove leaves, highly effective defoliants are needed that ensure more than 80% of cotton leaves fall in one treatment at low application rates, act “softly” on plants, and therefore do not negatively affect the oil content of seeds, yield, quality of cotton fiber and do not contaminate it [1, 2]. Meanwhile, sodium chlorate, a cotton defoliant produced in the republic and used, does not fully meet the modern requirements of cotton growing [3, 4]. The “harshness” of its effect on plants requires the creation of new effective defoliants that act softly on plants.

In this regard, special attention is paid to the production of highly effective, low-toxic and physiologically active defoliants. Existing chlorate-containing defoliants based on chlorates do not meet modern requirements for defoliants. It is known that the defoliating effect of chlorates is always accompanied by a desiccation effect to some extent [5, 6]. In the synthesis of new effective defoliants, the use of ethanolammonium sulfate, which is a plant growth stimulator, is of considerable interest. Consequently, as a result of adding this substance to the defoliant, the preparation acquires physiological activity [7].

Materials and methods

The objects of the study are sodium chlorate and monoethanolammonium sulfate. Sodium chlorate salt of chemically pure grade was used in purified form after recrystallization. Monoethanolammonium sulfate was synthesized on the basis of 94% sulfuric acid and 90% monoethanolamine obtained in a molar ratio of 1:2. At a temperature of 25 °C it is a brownish, thick and viscous solution with a pH of 6.36.

The solubility polytherm of the NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O system was investigated by the visual polythermal method [8]. Liquid nitrogen was used as a freezing reagent in the study of solution solubility.

In quantitative chemical analysis of liquid and solid phases, the carbonate ion concentration (CO₃^2-) was determined by the volumetric permanganatometric method [9]. The sodium ion concentration (Na⁺) was determined by the flame photometry method [10]. The chlorine ion (Cl^–) concentration was measured by the Mohr method [11]. Elemental analysis for carbon, nitrogen, hydrogen was carried out according to the method [12].

Results and discussions

The solubility of the NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O system was studied using seven internal sections. Based on the results of studying binary systems and internal sections, a complete polythermal diagram of this system was constructed in the temperature range from -18.5 to 38.0°С.

In the phase diagram of solubility of the NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O system, the crystallization fields of ice, sodium chlorate, monoethanolammonium sulfate and a compound of the composition Na₂SO₄·NH₂C₂H₄OH are delimited. The indicated fields converge at two triple nodal points of the system, for which the equilibrium solution compositions and the corresponding crystallization temperatures are determined, which are given in Fig. 1 and Table 1.

On the solubility diagram of the NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O system, solubility isotherms are plotted every 10°C. Projections of polythermal curves on the corresponding lateral water sides of the system are constructed. It is evident from the solubility diagram (Fig. 1) that a new compound of the composition Na₂SO₄·NH₂C₂H₄OH is formed in the studied system.

 Figure 1. Polythermal diagram of solubility of the NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O system

Table 1.

Double and triple points of the system NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O

To identify the new compound, we isolated crystals of the compound from the supposed crystallization region and studied them using chemical methods of analysis. Chemical analysis yielded the following results:

• found mass %: Na⁺ - 22.64; SO₄²⁻ - 47.29; NH₂C₂H₄OH -30.07
• calculated mass %: Na⁺ - 21.35; SO₄²⁻ - 48.16; NH₂C₂H₄OH -30.49

The new compound formed in the system is soluble in water at -10 and 0 °C by 54.3 and 72.4%, respectively. It dissolves well in organic solvents – ethyl alcohol, is insoluble in toluene and chloroform, and when dissolved in acetone, excess triethanolamine in the compound is washed out, and it remains in a pure white crystalline state. It was found that the resulting compound can be used as a cleaning agent for analysis in modern devices using acetone.

Conclusion

Thus, when studying the solubility diagram of the NaClO₃–H₂SO₄·NH₂C₂H₄OH–H₂O system, we established the formation of a new compound Na₂SO₄·NH₂C₂H₄OH, which was identified and confirmed by chemical analysis methods. The obtained data on the solubility of the components in the above system are the scientific basis for obtaining a new defoliant based on sodium chlorate and monoethanolammonium sulfate.

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