INVESTIGATION OF AQUEOUS SYSTEMS CONTAINING METHYL ACETATE, MONOETHANOLAMINE, UREA, AND AMMONIUM NITRATE

ABSTRACT

The methyl acetate – monoethanolamine – water system was studied using the isomolar series method, and based on the obtained data, a composition–property diagram was constructed. As a result of the interaction between methyl acetate and monoethanolamine, a new compound, N-acetylmonoethanolamine, was synthesized, and its composition was confirmed by physicochemical methods of analysis. The urea – N-acetylethanolamine – water system was also investigated using the isomolar series method. Based on the obtained data, a compound with the composition СО(NH₂)₂·CH₃CONHC₂H₄OH was isolated, and its structure and composition were confirmed by physicochemical research methods.

In addition, the ammonium nitrate – N-acetylethanolamine – water system was studied by the visual polythermal method, and a polythermal solubility diagram was constructed. The studies showed that no new compound is formed in this system

АННОТАЦИЯ

Система метилацетат – моноэтаноламин – вода была исследована методом изомолярных серий, и на основании полученных данных была построена диаграмма «состав–свойство». В результате взаимодействия метилацетата и моноэтаноламина было синтезировано новое соединение — N-ацетилмоноэтаноламин, состав которого подтверждён физико-химическими методами анализа. Система карбамид – N-ацетилэтаноламин – вода также была исследована методом изомолярных серий. На основании полученных данных было выделено соединение состава СО(NH₂)₂·CH₃CONHC₂H₄OH, структура и состав которого подтверждены физико-химическими методами исследования. Кроме того, система нитрат аммония – N-ацетилэтаноламин – вода была изучена визуально-политермическим методом, и была построена политермическая диаграмма растворимости. Исследования показали, что в данной системе новое соединение не образуется.

Keywords: methyl acetate, monoethanolamine, N-acetylethanolamine, urea, ammonium nitrate, solubility diagram, composition–property diagram.

Ключевые слова: метилацетат, моноэтаноламин, N–ацетилэтаноламин,  карбамид, нитрат аммония,  диаграмма растворимости, диаграмма “состав-свойства”.

Introduction. In the production of synthetic food-grade acetic acid, a low-boiling fraction is formed as a by-product with the following composition (wt.%): acetic acid 26.0–27.0; formic acid 4.0–8.0; methyl acetate 1.0–2.0; the remainder is water [1]. During the production of one ton of acetic acid, 0.87–0.90 kg of this waste is generated. JSC “Navoiazot” produces approximately 8.0–10.0 thousand tons of acetic acid per year. Thus, about 7.0–7.2 tons of the low-boiling fraction are generated annually at the enterprise.

The low-boiling fraction contains monocarboxylic acids, which can be used to obtain physiologically active substances by treating it with monoethanolamine. The physiologically active substances obtained in this way are modified complex preparations exhibiting highly effective stimulating properties that promote the growth and development of agricultural crops.

Materials and Methods. The work [2] is devoted to the study of the interaction of monoethanolamine with inorganic acids and their salts. In study [3], the results of investigations using concentrated solutions of acetic acid, formic acid, and monoethanolamine at 20 °C are presented, as well as studies in aqueous solutions [4,5,6]. However, the interaction of monoethanolamine with methyl acetate in aqueous solutions has not been previously investigated.

The system “methyl acetate–monoethanolamine–water” was studied [7] to establish the mechanism of their interaction. The isotherms of refractive index, density, viscosity, and pH exhibit inflection points corresponding to 20% and 50% concentrations of monoethanolamine solutions (Fig. 1).

Results and Discussion. Analysis of the isotherms leads to the conclusion that the interaction of monoethanolamine with methyl acetate in an aqueous solution results in the formation of N-acetylethanolamine. This compound was synthesized using concentrated monoethanolamine and methyl acetate. Elemental analysis of the synthesized compound was performed to determine its carbon, hydrogen, and nitrogen contents.

Figure 1. Methyl acetate–monoethanolamine–water system.

 (1) pH of the medium; (2) viscosity; (3) density; (4) refractive index

To establish the individuality and phase structure of the N-acetylethanolamine compound, its IR spectrum was studied (Fig. 2). A comparative analysis of the IR spectra of the compound CH₃CONHC₂H₄OH and the initial substances—monoethanolamine and methyl acetate—shows that the formation of N-acetylethanolamine is accompanied by changes in the above-mentioned IR spectrum of the compound.

Figure 2. IR spectra of the components of the methyl acetate–monoethanolamine–water system and the N-acetylethanolamine compound:

1 – methyl acetate; 2 – monoethanolamine; 3 – N-acetylethanolamine.

The IR spectrum of the synthesized compound exhibits the following absorption bands:
ν(OH) = 3354 cm⁻¹; ν(NH) = 3354 cm⁻¹; ν(CH₂) = 2878 cm⁻¹; ν(C=O) = 1639 cm⁻¹; δ(NH) = 1564 cm⁻¹; δ(CH₃, CH₂) = 1376 and 1306 cm⁻¹; ν(C–N) = 1308 cm⁻¹; ν(C–O) = 1308 cm⁻¹; ν(C–O) = 1069 cm⁻¹. The short-wavelength shifts of the absorption bands corresponding to the ν(C=O) and δ(NH) vibrations of the initial reagents, as well as the absence of absorption bands characteristic of ester groups in the product, indicate the formation of an amide fragment. This confirms that the synthesized compound, N-acetylethanolamine, is an individual substance with the chemical formula CH₃CONHC₂H₄OH (Fig. 2).

The ^1H and ^13C NMR spectra of N-acetylethanolamine were investigated using nuclear magnetic resonance spectroscopy. In the ^1H NMR spectrum of the synthesized compound recorded in dimethyl sulfoxide (DMSO-d₆), a singlet at 1.76 ppm was observed, corresponding to the methyl protons adjacent to the carbonyl group (C=O). Signals at 3.05 and 3.35 ppm correspond to two methylene (CH₂) groups coupled to each other, forming a quartet (J = 6.0 Hz) and a triplet (J = 6.0 Hz), respectively. In the weak-field region, a signal corresponding to the NH group appears at 7.94 ppm (Fig. 3).

Figure 3. ^1H NMR spectra of N-acetylethanolamine

To determine and establish the sequence of functional groups, the method of secondary resonance was employed. In this method, as in the parent compound methyl acetate, the C=O group is coupled with the CH₃ group, resulting in the corresponding signal at δ = 1.76 ppm. At the same time, through interaction via secondary frequency resonance involving the monoethanolamine –NH₂ group coupled with the –CH₂– group, additional resonance signals are also formed (Fig. 4).

Figure 4. ^13C NMR spectra of N-acetylethanolamine

Based on the analysis, it was established that in the ^13C NMR spectrum of the synthesized compound, signals of three carbon nuclei are observed in the high-field region at δ = 22.66, 41.77, and 60.03 ppm. In the low-field region of the spectrum, at δ = 169.92 ppm, a signal corresponding to the carbonyl carbon (C=O) group was detected (Fig. 4).

Figure 5. Secondary resonance spectra of N-acetylethanolamine

Comparison of the obtained NMR results shows that the synthesized compound contains four carbon atoms (Fig. 5). Based on the “Distortionless Enhancement by Polarization Transfer (DEPT)” experiment, it was determined that one carbon corresponds to a CH₃ group, two α-carbons correspond to –CH₂– groups, and the remaining carbon is a quaternary carbon of N-acetylethanolamine. From these investigations, it was established that the compound has the chemical formula CH₃–CO–NH–CH₂–CH₂–OH and is identified as N-acetylethanolamine.

The interaction behavior in the system “urea–N-acetylethanolamine–water” was studied. The isotherms of refractive index, density, viscosity, and pH exhibited inflection points corresponding to 50.0 mol% urea (Fig. 6), i.e., a molar ratio of urea to N-acetylethanolamine of 1:1. Thus, the observed inflection points in the studied system confirm the formation of a single new compound—urea–N-acetylethanolamine, with a 1:1 molar ratio of the starting components.

Figure 6. Urea–N-acetylethanolamine–water system:

 (1) pH of the medium; (2) refractive index; (3) viscosity; (4) density

For the compound CO(NH₂)₂·CH₃CONHC₂H₄OH, the following physicochemical properties were determined: crystallization temperature –60.0 °C, refractive index – n²⁰ = 1.5440; density – d²⁰ = 1.3023 g/cm³; viscosity – η²⁰ = 32.34 mm²/s; pH of the medium – 11.0.

To establish the individuality and phase structure of CO(NH₂)₂·CH₃CONHC₂H₄OH, its IR spectra were investigated. Comparative analysis of the IR spectra of CO(NH₂)₂·CH₃CONHC₂H₄OH and the starting materials—urea and N-acetylethanolamine—shows that the formation of CO(NH₂)₂·CH₃CONHC₂H₄OH leads to changes in the IR spectrum of the compound. For example, the amide band at 1681 cm⁻¹ shifts to the lower frequency region by 20 cm⁻¹ (1661 cm⁻¹). The absorption band of CH₃CONHC₂H₄OH–H₂O at 1639 cm⁻¹ shifts to a higher frequency by only ~3 cm⁻¹. Based on the above, it can be assumed that both intermolecular and hydrogen bonding exist between the >C=O group of urea and the –OH group of monoethanolamine. The IR spectra of the –OH group are observed in the region of intense valence vibrations of the amine groups of urea.

The polythermal solubility of the ammonium nitrate–N-acetylethanolamine–water system was studied using eight internal sections by the visual polythermal method. Sections I–IV were conducted from the N-acetylethanolamine–water side toward the apex of ammonium nitrate, and sections V–VIII from the ammonium nitrate–water side toward the apex of N-acetylethanolamine.

The binary system N-acetylethanolamine–water was studied for the first time and exhibits a eutectic point at 38.0 °C, corresponding to 17.4% water and 82.6% N-acetylethanolamine.

Based on the polythermal sections and the data from the side binary systems, a solubility diagram of the ammonium nitrate–N-acetylethanolamine–water system was constructed, covering the temperature range from complete freezing at –47.8 °C to 60 °C (Fig. 7).

Figure 7. Binary system of N-acetylethanolamine–water

Figure 8. Polythermal solubility diagram of the NH₄NO₃–CH₃CONHC₂H₄OH–H₂O system

Within the studied temperature and concentration range, the crystallization fields of ice, N-acetylethanolamine, and the α, β, and γ modifications of ammonium nitrate were identified. The system is characterized by a single ternary invariant point corresponding to 11.6% ammonium nitrate and 77.8% N-acetylethanolamine at –47.8 °C.

According to the polythermal solubility diagram, the formation of new chemical compounds was not observed. The studied system corresponds to a simple eutectic type (Fig. 8).

Previously, we studied the systems CO(NH₂)₂–CH₃CONHC₂H₄OH–H₂O and NH₄NO₃–CH₃CONHC₂H₄OH–H₂O. To justify the process of obtaining a new liquid fertilizer based on urea–ammonium nitrate solution (UAN), containing the physiologically active substance N-acetylethanolamine, the mutual influence of components in the system N-acetylethanolamine–[45% CO(NH₂)₂ + 55% NH₄NO₃]–water was investigated by the isomolar method.

The isotherms of refractive index, density, and pH of the studied system show that the inflection points correspond to 50.0 and 72.0 mol% of the total salts [45% CO(NH₂)₂ + 55% NH₄NO₃] (Fig. 9), i.e., a molar ratio of urea to N-acetylethanolamine of 1:1.

Figure 9. N-acetylethanolamine–[45% urea + 55% ammonium nitrate]–water system: (1) pH of the medium; (2) refractive index; (3) viscosity; (4) density.

Thus, the observed inflection points confirm the formation of a single new compound—N-acetylethanolamine with urea—at a 1:1 molar ratio. On the isotherms of medium pH, refractive index, and viscosity, these characteristic inflection points appear less distinctly.

From the liquid phase, a complex salt—urea–N-acetylethanolamine—was also isolated, with a molar ratio of 1:1.

Conclusion. Therefore, the study of the above-mentioned system demonstrates that the obtained results on rheological properties and solubility, as well as the optimization of synthesis conditions, sufficiently substantiate the possibility of obtaining a new liquid fertilizer based on urea–ammonium nitrate and N-acetylethanolamine.

References:

1. TU 6.1-00203849-08:2004, Amendment No. 1, Synthetic Food-Grade Acetic Acid.
2. Khasanova, V.M.; Saibova, M.T.; Ismatlova, G.Kh. Study of the Interaction of Monoethanolamine with Sulfuric Acid. Journal of Inorganic Chemistry –Moscow, 1983, Vol. 28, No. 1, pp. 228–331.
3. Abdullaeva, M.T., Narkhodzhaev A.Kh., Tadzhieva Kh.S. Physicochemical Foundations for the Production of Nitrogen Fertilizers Containing Growth-Stimulating Substances. Universum: Technical Sciences: Scientific Journal. No. 9, Moscow, 2020, pp. 36–39.
4. Abdullaeva, M.T. Interaction of Monoethanolamine with Acetic Acid. Uzbek Chemical Journal – Tashkent, 2008, No. 3, pp. 5–7.
5. Narkhodzhaev, A.Kh.; Abdullaeva, M.T.; Adilova, M.Sh. Study of the Interaction of Monoethanolamine with Formic Acid. Chemistry and Chemical Technology – Tashkent, 2009, No. 1, pp. 34–36.
6. Аbdullaeva M.T., Karazhanova Sh.D., Saydullaeva G.A. Study of Solubility in the System: Potassium Salt–Monoethanolammonium Acetate–Water. Universum: Technical Sciences: Scientific Journal. No. 1, Moscow, 2025, pp. 53–56.
7. Abdullaeva, M.T. Interaction of Methyl Acetate with Monoethanolamine. In: Proceedings of the Republican Scientific-Technical Conference “Development of Efficient Technologies for the Production of Mineral Fertilizers and Next-Generation Agrochemicals and Their Practical Application” – Tashkent, 2010, p. 142.