A NEW THREE-STEP PROCEDURE FOR THE SYNTHESIS OF CYANURIC ACID
795
or returned into the production cycle for preparing
HMDS:
Cyanuric acid I was obtained in an amount of 90.7 g,
yield 93%. Mass spectrum, m/z (relative intensity, %): 129
+
·
+·
+·
(
100, M ), 86 (12, [HNCO] ), 43 (40, [HNCO] ). IR
2
(
Me Si) О + HCl → Me SiCl,
–1
3
2
3
spectrum (KBr), ν, cm (transmittance, %): 3150 (67),
3
1
115 (50), 3025 (25), 2780 (35), 1780 (40), 1770 (20),
725 (3), 1468 (40), 1400 (15), 1050 (50), 775 (35). The
Me SiCl + NH → (Me Si) NH.
3
3
3
2
Thus, the suggested procedure for preparing pure
cyanuric acid is low-waste and less power-consuming
compared to direct pyrolysis of urea. It can be recom-
mended for commercial low-tonnage production.
product was analyzed for the main substance content
by potentiometric titration of the preliminary prepared
sodium salt of I with hydrochloric acid. The main sub-
stance content was 99–99.3%. In a similar synthesis,
when isocyanate II was added in the temperature interval
7–9°С, 70 g of acid I was obtained, yield 72%; at 20°С,
the yield was 29.3 g (30%).
EXPERIMENTAL
Trimethylsilyl isocyanate II. The reboiler (1.5 L)
of a fractionation column (diameter 10, length 550 mm)
packed with glass rings 1.5 mm in diameter was charged
with 180 g (3 mol) of dry urea, after which 500 g of a mix-
ture of xylenes, 260 g (1.615 mol) of HMDS, and several
drops of concentrated sulfuric acid were added. The
mixture was heated with stirring until ammonia started to
evolve (65–70°С), after which it was kept for 30–45 min
at 70–100°С. Then the temperature in the reboiler was
raised to 140–145°С, and trimethylsilyl isocyanate II
The mother liquor after isolating cyanuric acid was
distilled on a column to completely regenerate acetone
and obtain 180 g of hexamethyldisiloxane (yield 98.3%)
as the second fraction (boiling point 98–102°С).
CONCLUSIONS
(1) A procedure for preparing trimethylsilyl isocya-
nate by the reaction of urea with hexamethyldisilazane
in a mixture of xylenes in the presence of sulfuric acid
as catalyst was tested. It proved to be highly efficient.
(
puirity no less than 99%) was taken off at the vapor
temperature of 91–92°С over a period of 5–6 h. Yield of
I 293–310 g (85–90%). The bottoms contained xylene,
the unchanged HMDS, and 0.2–0.5 wt % isocyanate II.
The bottoms were distilled in a vacuum and reused with
loading fresh portions of the reactants.
(
2) Hydrolysis of trimethylsilyl isocyanate at low
temperatures in acetone in the presence of triethylamine
as catalyst can be used for low-tonnage production of
high-purity cyanuric acid.
Hydrolysis of isocyanate II to cyanuric acid I.
REFERENCES
Amixture of 920 g of acetone, 2.6 g of triethylamine, and
4
2
1.4 g (2.3 mol) of distilled water was cooled to 0°С, and
60 g (2.26 mol) of isocyanate II was added dropwise
1. RF Patent 2059625, Publ. 1996.
2. Kozyukov, V.P., Dobrovinskaya, E.K., and Mironov, V.F.,
Zh. Obshch. Khim., 1976, vol. 46, no. 7, pp. 1531–1533.
with vigorous stirring at a rate allowing the temperature
to be maintained in the interval 0–5°С. After adding the
whole amount of the isocyanate, the reaction mixture
was stirred for 4 h at 2–4°С and filtered. The precipitate
was washed twice with acetone and dried in a vacuum.
3. Kozyukov, V.P., Sheludyakov, V.D., and Mironov, V.F., Usp.
Khim., 1973, vol. 42, no. 8, pp. 1451–1480.
4. Fedotov, N.S., Abramov, A.V., and Sheludyakov, V.D., Zh.
Obshch. Khim., 1987, vol. 57, no. 3, pp. 579–584.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 87 No. 6 2014