to chemical modifications, but makes it possible to separate the products: mercaptotriazinone 1a precipitates
from the cooled alkaline solution (it was discarded by the authors of [1] as an impurity) and has mp 191-192°C;
the second product with mp 172-173°C (coinciding with that indicated in [1] for compound 1a) precipitates
from the strongly acidified filtrate. According to 1H NMR and mass spectroscopy data, the latter product can be
definitely assigned the structure of 2-methyl-2-thiosemicarbazidopropanoic acid (3). Thus in [1], the structure of
mercaptotriazinone 1a was erroneously assigned to acid 3, and the reaction of acetone cyanohydrin with
thiosemicarbazide in aqueous medium occurs differently than assumed. Although formation of the intermediate
nitrile 2 is obvious, it is doubtful that it can survive in hot aqueous medium. More likely, under the reaction
conditions it is either hydrolyzed with formation of the corresponding acid or undergoes ring closure to form
5-imino-3-mercapto-6,6-dimethyltriazine, the hydrolysis of which also leads to the final mercaptotriazinone 1a.
The poor solubility of the latter in basic medium is obviously explained by the predominance of the thione form 1b.
Attempts to make acid 3 undergo ring closure in aqueous acid, neutral or basic medium were
unsuccessful. However, heating it in dioxane with boric acid makes it possible to obtain a compound isomeric to
1, 2-amino-5,5-dimethyl-1,3,4-thiadiazin-6-one (4).
EXPERIMENTAL
The course of the reaction and the purity of the substances obtained were monitored by TLC on Silufol
1
UV-254 plates; the eluent was chloroform–ethyl acetate, 3:1. The H NMR spectra were taken on a
Bruker AC-300 (300 MHz) in DMSO-d6 relative to TMS; the mass spectra were taken on an LKB 9000,
ionizing electron energy 70 eV.
Reaction of Acetone Cyanohydrin with Thiosemicarbazide. A mixture of acetone cyanohydrin
(0.1 mol) and thiosemicarbazide (0.1 mol) was held for 3 h in water (50 ml) at 95-100°C. The crystals that
precipitated after cooling were filtered out, washed with cold water, and dried. The crystals obtained (15 g)
were mixed with potassium carbonate (12 g) and water (40 ml), and held for 3 h at 95-98°C. After cooling from
basic solution, triazinone 1a precipitated, which was filtered out, washed with water, and recrystallized from
alcohol. Acid 3 precipitated from the filtrate acidified with HCl (pH 3-4), and was filtered out, washed with
water, and crystallized from alcohol.
1
3-Mercapto-6,6-dimethyl-1,2,4-triazin-5-one (1a). Yield 20%; mp 191-192°C. H NMR spectrum,
δ, ppm: 2.0 (6H, s, 2CH3); 7.2 (1H, s, NH); 7.8 (1H, s, NH); 9.7 (1H, s, SH). M 159 (mass spectrometrically).
Found, %: C 37.85; H 5.82; N 26.25; S 20.02. C5H9N3OS. Calculated, %: C 37.73; H 5.66; N 26.42; S 20.13.
1
2-Methyl-2-thiosemicarbazidopropanoic Acid (3). Yield 55%; mp 172-173°C. H NMR spectrum,
δ, ppm: 1.2 (6H, s, 2CH3); 5.5 (1H, s, NH); 7.4 (1H, s, NH); 7.6 (1H, s, NH2); 7.9 (1H, s, NH2); 12.7 (1H, s,
COOH). M 177 (mass spectrometrically). Found, %: C 34.15; H 6.52; N 23.45; S 18.22. C5H11N3O2S.
Calculated, %: C 33.90; H 6.21; N 23.73; S 18.08.
2-Amino-5,5-dimethyl-1,3,4-thiadiazin-6-one (4). A mixture of acid 3 (3.5 g) and anhydrous H3BO3
(1.2 g) was refluxed in dioxane (20 ml) for 10 h. After cooling, the boric acid was filtered out and the filtrate
was poured into water. The precipitate was filtered out, dried, and recrystallized from dioxane. Yield 60%;
mp 270-272°C. 1H NMR spectrum, δ, ppm: 1.2 (6H, s, 2 CH3); 5.8 (1H, s, NH); 10.4 (1H, s, NH2); 10.7 (1H, s,
NH2). M 159 (mass spectrometrically). Found, %: C 38.15; H 5.52; N 26.85; S 19.75. C5H9N3OS.
Calculated, %: C 37.73; H 5.66; N 26.42; S 20.13.
REFERENCES
1.
V. Kh. Khamaev, V. A. Danilov, R. N. Khannanov, and A. K. Mazitova, Zh. Org. Khim., 30, 777 (1994).
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