A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1925, 5, 85
DOI: 10.15227/orgsyn.005.0085
[Urea, nitro-]
Submitted by A. W. Ingersoll and B. F. Armendt.
Checked by Henry Gilman and C. C. Vernon.
1. Procedure
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).
2. Notes
1. If bubbles of gas begin to be evolved while stirring, the mixture should be poured at once upon ice.
2. A hardened filter is necessary. Whatman's No. 50 is satisfactory.
3. Cracks appear when the nitrourea is filtered; hence, care must be taken that the water used for washing does not go through the cracks instead of through the material. If desired, the nitrourea may be removed from the funnel, made into a paste with about 800 cc. of cold water, and again filtered.
4. The product may be dried on a steam plate if the heating is not continued too long.
5. Various samples of nitrourea prepared in this way melt differently, and therefore the melting point is not a suitable indication of purity. A uniform product can also be obtained by crystallizing one-half of the crude material obtained in one run from 1 l. of water at a temperature not over 55°, and using the filtrate to crystallize the second half. Even this recrystallized material does not have a definite melting point.
6. Nitrourea may be obtained in a pure condition by recrystallization from ether, benzene, or chloroform, in which solvents it does not dearrange, and melts sharply at 158.4–158.8° with decomposition.1
3. Discussion
Nitrourea can be prepared by the action of concentrated sulfuric acid on urea nitrate.2 The procedure described is essentially that of Thiele and Lachmann.2 A modified procedure3 uses a lesser quantity of sulfuric acid.
This preparation is referenced from:

References and Notes
  1. Willstätter and Pfannenstiel, Ber. 59, 1870 (1926); Davis and Blanchard, J. Am. Chem. Soc. 51, 1790 (1929).
  2. Thiele and Lachmann, Ann. 288, 281 (1895); Backer, Rec. trav. chim. 31, 21 (1912); Willstätter and Pfannenstiel, Ber. 59, 1870 (1926).
  3. Davis and Blanchard, J. Am. Chem. Soc. 51, 1794 (1929).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

sulfuric acid (7664-93-9)

Benzene (71-43-2)

ether (60-29-7)

chloroform (67-66-3)

Urea, nitro- (556-89-8)

urea nitrate

semicarbazide (57-56-7)