Org. Synth. 1947, 27, 71
DOI: 10.15227/orgsyn.027.0071
PSEUDOTHIOHYDANTOIN
[4-Thiazolidone, 2-imino-]
Submitted by C. F. H. Allen and J. A. VanAllan.
Checked by H. R. Snyder and Frank X. Werber.
1. Procedure
In a 1-l. flask surmounted by a reflux condenser, 76 g. (1 mole) of thiourea, m.p. 174–176°, is dissolved in 500 ml. of 95% ethanol by refluxing for 10–15 minutes. Then 125 g. (108 ml., 1.02 moles) of ethyl chloroacetate is added slowly (15–20 minutes) through the condenser while gentle refluxing is continued. After the mixture has been refluxed for 3 hours longer, it is allowed to cool to room temperature and the solid is filtered by suction on a 14-cm. Büchner funnel. The filtrate is used to rinse any solid adhering to the walls of the reaction flask onto the filter. The crude product is pressed down firmly and washed with 50 ml. of ethanol (Note 1).
The crude hydrochloride is dissolved in 1.2 l. of hot, freshly boiled water (Note 2) in a 2-l. beaker, a boiling solution of 121 g. of sodium acetate trihydrate in 150 ml. of water is added, and the mixture is heated to boiling (Note 3). The resulting clear solution is stored in the ice chest overnight. The crystalline pseudothiohydantoin is filtered and dried to constant weight at 60°. The product weighs 92–95 g. (79–82%). A reproducible decomposition point of 255–258° can be determined with the aid of a melting-point bar (Note 4).
2. Notes
1.
The yield of the crude
hydrochloride, dried to constant weight, is about
126 g.; the decomposition range is
210–255°.
2.
The water is boiled before use to expel dissolved
oxygen, the presence of which in the solution may cause the final product to have a yellow color.
3.
Prolonged boiling should be avoided, as hydrolysis of the imino group occurs very easily. When
sodium carbonate is substituted for
sodium acetate the yield drops 10%.
4.
The decomposition point as measured in the ordinary manner varies with the temperature of the bath at the time of the introduction of the sample. When the melting-point bath is heated so that the temperature rises by 2° per minute, a sample introduced just as the temperature reaches 200° develops an observable brown color at 206° and then darkens so rapidly that no liquid phase can be identified; if, under the same conditions, the sample is introduced when the bath temperature is 238° the decomposition begins immediately but a liquid phase can be recognized when the bath temperature is in the range 241–243°.
3. Discussion
Pseudothiohydantoin has been obtained from
thiourea and
ethyl chloroacetate1 and from
thiourea and
chloroacetic2,3 or dichloroacetic acids.
4
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Pseudothiohydantoin
chloroacetic
dichloroacetic acids
ethanol (64-17-5)
sodium acetate (127-09-3)
sodium carbonate (497-19-8)
oxygen (7782-44-7)
Ethyl chloroacetate (105-39-5)
thiourea (62-56-6)
sodium acetate trihydrate (6131-90-4)
4-Thiazolidone, 2-imino-
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