In a
3-l. beaker a mixture of
20 g. (0.146 mole) of anthranilic acid, 700 cc. of warm water (35°), and
11 cc. (11.6 g., 0.19 mole) of glacial acetic acid is stirred mechanically and allowed to cool to room temperature. A freshly prepared solution of
15 g. (0.185 mole) of potassium cyanate (Note
1) in 50 cc. of water is then added dropwise with stirring over a period of fifteen to twenty minutes (Note
2). The resulting pasty mixture is stirred for twenty minutes, and then
200 g. (5 moles) of flaked sodium hydroxide (Note
3) is added slowly in small portions. During this addition the reaction mixture is kept below 40° by cooling in a
cold-water bath. A clear solution is obtained momentarily, but in a short time a fine granular precipitate of the hydrated
monosodium salt of benzoylene urea precipitates. After the mixture has cooled overnight in an
ice box, the precipitated sodium salt is collected on a
Büchner funnel, using a
hardened filter paper (Note
4). The colorless salt is dissolved in 1 l. of hot water (90–95°), and the solution is filtered and heated to boiling in a
3-l. beaker. The
benzoylene urea is precipitated by adding dilute
sulfuric acid (1:1) with vigorous stirring until the liquor is acid to litmus. The product separates as a hydrate which forms small, lustrous, colorless needles. The material is collected on a Büchner funnel, washed with 200 cc. of water, and dried in an
oven at 100°. The yield is
19.5–20.5 g. (
82–87 per cent of the theoretical amount) (Note
5).