S. Chen et al
controlled under 10 ꢀC and stirred for 2 h, when TLC presented a clear
and centralized spot, and 10% sodium hydroxide solution was added
to neutralize the acid. About 1–2 h later, 0.99 g (0.020 mol) ethylamine
was added, and the temperature maintained at 15–20 ꢀC. After 1 h,
0.88 g (0.020 mol) NaOH was added to neutralize the acid, and the
reaction was stirred for 2 h. The layers were separated and crude product
was obtained from evaporating the chlorobenzene and triturating the
residue with petroleum ether. The product was a white powder obtained
in 95.4% yield (4.11 g, 0.019 mol). FT-IR (KBr) cmÀ1: 3260, 3117, 2974,
1620, 1551, 1439, 1403, 1384, 1346, 1261, 805. 1H-NMR (300 M, CDCl3)
d: 1.19–1.38 (m, 9H), 3.41–3.50 (m, 2H), 4.13–4.20 (m, 1H), 5.20–5.29
(m, 1H), 5.73–6.01 (m, 1H). HRMS (ESI, m/z): calcd mass for
12C153C3H14ClN5, [M + H]+: 219.10919; found: 219.11069. The 13C
abundance of the product was 99.05%.
Scheme 1. Synthesis of [13C3]cyanuric acid.
Results and discussion
Scheme 2. Synthesis of [13C3]cyanuric chloride.
Many papers and patents have reported synthesis of cyanuric
acid by the pyrolysis of urea in solvents solvent. An appropriate
solvent for this reaction must fit the following principles: the
solvent has a boiling point within the pyrolysis temperature
range; it can dissolve the urea but do not or slightly the cyanuric
acid; it can be well recovered and recycled.6 We finally choose
the sulfolane–cyclohexanol (Scheme 1) mixture as the solvent
because it could provide an appropriate reaction temperature
and the final product’s purity was higher than the normal indus-
trial method.7 It has been reported that the presence of ammo-
nia produced by urea decomposition would cause a higher
content of aminated by-product.8 Reduced pressure was
reported favorable for getting satisfying yield of the product.9
So, a vacuum pump was equipped at the end as a gas collecting
plant and to form a reduced pressure reaction environment.
Cyanuric chloride is a common reagent frequently used in
syntheses of the cyanuric acid.10 However, the reverse reaction
has seldom been reported. B.P. Bandgar and S.S. Sawant
describe the conversion of the cyanuric acid, recovered from
another reaction, to cyanuric chloride by treatment of a mixture
of the acid and N,N-diethylaniline with POCl3.11 In our method,
this step of reaction could be finished in one reactor, so it could
reduce the wastage of material and crude product during the
procedure. PCl5-POCl3 mixture has been reported as a well
chlorine provider for many compounds whose structures were
very similar with cyanuric acid.12–14 In this study, the mixture
was proved facilitating the cyanuric acid converting to cyanuric
chlorine as well and helped furnishing the product in yield of
71.4% (Scheme 2).
Benita Barton described a method to synthesis the atrazine
from cyanuric chloride as shown in Scheme 3 and also investi-
gated the reaction calorimetry so as to find an optimal addition
sequences and rates.15 It seems that this step from cyanuric
chloride to atrazine is quite straightforward, but labeled cyanuric
chloride is expensive and difficult to obtain. On the contrary,
labeled urea is a common material that is often employed to
label compounds and is much cheaper. In this paper, we
describe a simple method to label the atrazine from [13C]urea.
In summary, our work has developed a simple way to label the
widely used herbicide atrazine with overall yield of 57.6% and
chemical purity of 98.58%. The product is qualified to the
internal standard and could be used in detecting the ground
and underground water.
Scheme 3. Synthesis of [13C3]atrazine.
Acknowledgments
We are grateful to the ‘Eleventh Five-Year Plan’ technology
support project of China (No. 2009BAK61B04) and the ‘Twelve
Five-Year Plan’ technology support project of China (No.
2012BAK25B03-14) for the financial support.
Conflict of Interest
The authors did not report any conflict of interest.
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