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SOLVENT EFFECTS ON HIGH-PRESSURE CATALYTIC VINYLATION
OF CYANURIC ACID
Ziyadullayev Anvar Egamberdiyevich
Associate Professor, Tashkent Institute of Chemical Technology
Abdualimov Normurod Tokhir o'g'li
Master's student at the Tashkent Institute of Chemical Technology
To'rayeva Dilrabo Fakhriddinovna
PhD student at Tashkent Institute of Chemical Technology
Nigmatova Komila Kholiq qizi
Senior lecturer at the Tashkent Institute of Chemical Technology
Abstract. Background of the Problem.
Cyanuric acid and its derivatives are widely used in various industrial sectors.
They serve as monomers in polymer synthesis, agents for microbiological treatment
of natural water bodies and industrial wastewater, and chlorine stabilizers.
Additionally, they are used in the production of industrial dyes, surfactants,
pesticides, and herbicides for agricultural applications.
Objective:
To synthesize vinyl derivatives of cyanuric acid under homogeneous catalytic
conditions through its reaction with acetylene at high pressures and to determine the
optimal reaction parameters.
Methodology:
Vinyl esters of cyanuric acid were synthesized via a homogeneous catalytic method
under high-pressure conditions. The structure of the synthesized compounds was
confirmed using infrared (IR) spectroscopy.
Scientific Novelty:
Mono-, di-, and trivinyl esters of cyanuric acid were synthesized for the first
time via catalytic vinylation of acetylene in the presence of solvents.
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Results:
The synthesis of mono-, di-, and trivinyl esters of cyanuric acid under high-pressure
conditions was investigated. The influence of catalyst concentration, solvent nature,
reaction temperature, and duration on product yield was studied.
Keywords:
Cyanuric acid and its vinyl esters; vinylation; acetylene; high pressure;
catalytic reactions.
Highlights:
Mono-, di-, and trivinyl esters of cyanuric acid were synthesized.
The mechanism of cyanuric acid vinylation was discussed.
Factors affecting the yield of vinyl esters of cyanuric acid were
evaluated.
Introduction:
The properties of cyanuric acid and its derivatives have been extensively
studied by prominent scientists such as J. Liebig, F. Wöhler, A. W. Hofmann, I. V.
Gauthier, O. Laurent, C. F. Gerhardt, C. A. Wurtz, and F. F. Beilstein. Nevertheless,
the vinylation, isomerism, and other chemical characteristics of cyanuric acid and its
derivatives require further in-depth investigation [1–4].
Cyanuric acid is widely used as a key reagent in the thermal processing of
polymers such as polyphenylacetylene, microcrystalline cellulose, polyvinyl alcohol,
polysulfone, polycarbonate, and polyvinyl chloride. Its presence in many
technological processes not only accelerates chemical reactions under high-pressure
conditions but also enhances the reactivity of chemical systems. For this reason, the
chemical activity of cyanuric acid under elevated pressures has been a subject of
particular interest in various studies [5–6].
Materials and Methods
The vinylation reaction of cyanuric acid was carried out under homogeneous
catalytic conditions in an RCG 1.6-100/6 K1-type reactor at a pressure of 10 atm. The
process was conducted with acetylene gas at varying temperatures and reaction times.
Acetylene (supplied from a cylinder) was used as the vinylating agent, while zinc
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oxide (ZnO) served as the catalyst. Dimethylformamide (DMF) and dimethyl
sulfoxide (DMSO) were used as solvents.
The resulting reaction mixture was extracted with diethyl ether. The organic
phase was separated, and the solvent was removed. The residue was then subjected to
vacuum fractional distillation for further purification.
Infrared (IR) spectra of the synthesized compounds were recorded using
“Specord-75”, “Shimadzu”, or “UR-70” spectrophotometers in the range of 400–4000
cm⁻¹. The samples were analyzed either in solution or as neat films.
IR Spectroscopic Characterization
Monovinyl ester of cyanuric acid:
Characteristic IR absorption bands (cm⁻¹):
3512 (–OH), 1765 (C=O), 1384 (C=N), 1093 (C–OH), 1253 (C–O–C), 864
(═CH₂), 1471 (=CH), 1660 (–CH=CH₂).
Divinyl ester of cyanuric acid:
Characteristic IR absorption bands (cm⁻¹):
3493 (–OH), 1759 (C=O), 1386 (C=N), 1091 (C–OH), 1253 (C–O–C), 864
(═CH₂), 2929 and 1438 (=CH), 1654 (–CH=CH₂).
Trivinyl ester of cyanuric acid:
Characteristic IR absorption bands (cm⁻¹):
1791 (C=O), 1400 (C=N), 1056 (C–O–C), 761 (═CH₂), 3053 and 1463
(=CH), 1693 (–CH=CH₂).
Results and Discussion
The synthesis of vinyl derivatives of cyanuric acid was initially performed
under atmospheric pressure conditions, as previously reported [7–9]. Further
reactions were carried out at pressures ranging from 1 to 20 atm in the presence of
dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) as solvents, with zinc
oxide (ZnO) as a catalyst.
As a result of these experiments, mono-, di-, and trivinyl esters of cyanuric
acid were successfully obtained. The vinylation reaction proceeds via a nucleophilic
substitution mechanism.
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The proposed reaction scheme and the possible mechanistic pathway are
illustrated below:
The influence of pressure, temperature, and solvent type on the product yield
was systematically studied. It was found that increased pressure and the use of polar
aprotic solvents significantly improved the yield and selectivity of vinylated products.
The nucleophilic substitution mechanism is favored due to the electron-
deficient triazine ring of cyanuric acid, which facilitates attack by the vinylating agent
(acetylene) at the hydroxyl functional groups. The formation of mono-, di-, and
trivinyl esters is largely dependent on the molar ratio of acetylene to cyanuric acid
and the duration of the reaction.
These findings demonstrate the effectiveness of ZnO as a catalyst under
relatively mild conditions and highlight the importance of optimizing reaction
parameters for selective synthesis of cyanuric acid vinyl esters.
The vinylation reaction likely proceeds through the initial coordination of
cyanuric acid with ZnO, forming a reactive intermediate. This coordination activates
the hydroxyl groups on the triazine ring, making them more susceptible to
nucleophilic attack by acetylene. The sequential substitution results in the formation
of mono-, di-, and trivinyl esters, depending on the stoichiometry and reaction
conditions.
The resulting zinc hydroxide compound reacts with acetylene to form an
intermediate product, namely a vinyl-substituted zinc hydroxide derivative.
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Under elevated temperature and high pressure, the vinylated zinc hydroxide
complex transforms into the monovinyl ester of cyanuric acid, with the concurrent
release of zinc oxide.
The reaction of the monovinyl ester with acetylene leads to the formation of
the divinyl ester of cyanuric acid.
According to this mechanism, the divinyl ester can further react to form the
trivinyl ester of cyanuric acid.
The vinylation reaction of cyanuric acid was carried out at a pressure of 1–20
atm for 2–6 hours at a temperature range of 100–160°C. To accelerate the reaction,
increase the efficiency of the process, and minimize the risk of acetylene
decomposition, the reaction mixture was diluted with an inert gas—nitrogen.
The effects of reaction time, temperature, and pressure on the synthesis of
vinyl esters during the vinylation of cyanuric acid in the presence of DMSO + ZnO
and DMF + ZnO were investigated.
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When the reaction was conducted for 2 hours in the presence of DMSO and
ZnO at a pressure of 10 atm, the yield of the monovinyl ester was higher than that of
the di- and trivinyl esters (see Fig. 1).
Figure 1.
Effect of DMSO + ZnO on the yield of vinyl esters of cyanuric acid
Analysis of the results
shows that the introduction of acetylene in the
presence of the DMSO + ZnO system for 2 hours at temperatures of 100, 120, and
140°C and a pressure of 10 atm leads to the synthesis of monovinyl ester with yields
of 34.6%, 40.4%, and 52.6%, respectively; divinyl ester – 8.4%, 10.8%, and 12.4%;
and
trivinyl
ester
–
6.2%,
8.6%,
and
10.2%.
When the reaction was carried out at 160°C, the yields of the vinyl esters decreased
to 20.8%, 6.8%, and 4.6%, respectively.
Vinylation of cyanuric acid was also performed with a reaction time of 4 hours
in a DMSO solution in the presence of ZnO at temperatures ranging from 100 to
160°C (Table 1).
Table 1. Effect of temperature on the yield of vinyl esters of cyanuric acid in
the DMSO + ZnO system (reaction duration 4 hours)
Temperature (°C) Monovinyl ester (%) Divinyl ester (%) Trivinyl ester (%)
100
61.5
13.6
10.4
120
64.7
15.9
12.6
140
68.4
18.4
13.3
160
44.5
11.2
7.8
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Results and Discussion
The results showed that as the temperature increased in the range of 100–
160 °C over a reaction duration of 4 hours, the yield of vinyl esters of cyanuric acid
passed through a maximum. At 140 °C, the yields of mono-, di-, and trivinyl esters
were 16.4%, 46.8%, and 18.0%, respectively. A further increase in temperature led to
a decrease in the yields. For example, at 160 °C, the yields of mono-, di-, and trivinyl
esters decreased to 6.6%, 20.8%, and 8.6%, respectively.
It is noteworthy that in all cases, the yield of the divinyl ester was higher than
that of the mono- and trivinyl esters.
Additionally, the synthesis of vinyl esters of cyanuric acid was studied in the
presence of the DMF–ZnO system (Fig. 2).
Fig. 2. Effect of DMF + ZnO on the yield of vinyl esters of cyanuric acid
(reaction duration: 2 hours)
Analysis of the results showed that at 100 and 140°C, the yields were as
follows: (I) monovinyl ester – 32.6% and 46.5%; (II) divinyl ester – 8.2% and
12.2%;
(III)
trivinyl
ester
–
4.8%
and
4.2%,
respectively.
The effect of temperature on the reaction of cyanuric acid with acetylene under
high pressure for 4 hours in the DMF + ZnO system was also studied (Table 2).
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Results showed that when using DMF as a solvent, the process
productivity was significantly lower compared to DMSO. The catalytic effect of
DMSO is explained by the fact that during the vinylation of cyanuric acid,
acetylene is activated more effectively in the DMSO+ZnO system than in the
DMF+ZnO system. The influence of temperature (100–160°C) on the yield of
vinyl ethers was also investigated for a reaction duration of 6 hours in both
DMF+ZnO and DMSO+ZnO systems (see Fig. 3).
Figure 3. Effect of temperature on the yield of divinyl ether of cyanuric acid with
a reaction duration of 6 hours in the systems DMFA + ZnO (1) and DMSO +
ZnO (2).
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The comparative analysis of experimental results showed that, with a
reaction duration of 6 hours, the yield of the product in both systems increased
with temperature and reached a maximum at 140 °C — 70.6% in the DMF
system and 76.5% in the DMSO system.
It should be noted that when the reaction time was extended to 6 hours and
the temperature was raised from 100 to 160 °C, the yield of the trivinyl ether in DMSO
was higher than that of the mono- and divinyl ethers. In particular, at 100, 120, and
140 °C, the trivinyl ether yield was 46.6%, 58.4%, and 76.5%, respectively. However,
further temperature increases beyond 160 °C led to a sharp decrease in the yield of
the products.
Conclusion.
In the vinylation of cyanuric acid, the DMSO + ZnO system was
found to be significantly more efficient than the DMF + ZnO system. Under a pressure
of 10 atm and a temperature of 140 °C, the optimal reaction durations for synthesizing
the mono-, di-, and trivinyl ethers were determined to be 2 hours (52.6%), 4 hours
(46.8%), and 6 hours (76.5%), respectively.
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