A.
1-Phenyl-2-thio-4-methylisobiuret. Into a
500-ml. three-necked flask fitted with a
Hershberg stirrer2 and
reflux condenser are introduced a solution of
23.0 g. (0.35 mole) of 85% potassium hydroxide in 75 ml. of water, followed by
38.7 g. (0.35 mole) of methylisourea hydrochloride (Note
1). The clear liquid is diluted with
150 ml. of acetone, and the resulting suspension, containing finely divided crystalline solid, is treated with
27.0 g. (24 ml., 0.2 mole) of recently distilled phenyl isothiocyanate.
After the additions have been completed, the third neck of the flask is closed and the temperature of the stirred reaction mixture is raised to its boiling point during 15–20 minutes, then heating under reflux is continued for 10–15 minutes. The contents of the flask, which first change to a greenish yellow clear solution, then later separate into two phases, are kept well mixed by rapid stirring (Note
2). The flask is next disconnected, fitted with a stillhead, and the
acetone is distilled rapidly at 25–35° under reduced pressure. The residual semicrystalline suspension, or two-phase mixture containing the crude product in the upper viscous layer, is carefully stirred onto 300–400 g. of crushed ice. This yields the crude isobiuret as a very pale-yellow granular solid, which is collected by suction filtration, washed with successive small portions of water, drained well, and allowed to dry at room temperature. The dry product is dissolved
120–150 ml. of boiling benzene. Small quantities of suspended yellow powdery material (and possibly droplets of water) are removed by gravity filtration through a heated funnel or by suction filtration through a preheated
Büchner funnel. The clear yellow filtrate deposits large prismatic crystals of
1-phenyl-2-thio-4-methylisobiuret, which are collected by suction filtration at room temperature, washed with a little
benzene, and air-dried. The yield of material having a melting point in the range of
122–128° is
27–31.5 g. (
65–75%) (Note
3). Further small quantities (
2–4 g.) of less pure material may be obtained by partial vacuum evaporation of the combined mother liquors and washings.