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).