In a
2-l. Erlenmeyer flask provided with a
mechanical stirrer and
thermometer, and surrounded by an ice-salt mixture, is placed
700 cc. of concentrated sulfuric acid. The stirrer is started, and when the acid is cooled to −3° or below,
200 g. (1.62 moles) of dry, powdered urea nitrate is added in small portions at such a rate that the temperature does not rise above 0°. The addition will require about one-half hour. Stirring is continued for another one-half hour, the temperature being kept below + 3° (Note
1). Then the mixture is poured upon 1 kg. of ice.
The white, finely divided precipitate of
nitrourea is filtered upon a
12-cm. Büchner funnel. A
hardened filter paper (Note
2) is used in this operation, and the
nitrourea is pressed as dry as possible. The product is washed in the funnel with four portions of cold water just sufficient to cover it, and pressed dry each time (Note
3). Then it is dried in the air (Note
4). By strongly cooling the filtrates, a further small amount of
nitrourea may be obtained and added to the main portion. The yield of air-dried material is
120–150 g. (
70–87 per cent of the theoretical amount). It melts with decomposition at
150–164° and is sufficiently pure for use in the preparation of
semicarbazide (Note
5) and (Note
6).