L-Phenyl-2-thio-4-methylisobiuret

Phenylpyruvic acids by hydrolysis of phenylhydantoins, 43, 49 1-Phenyl-2-THiOBiuRET, 42, 87 l-Phenyl-2-thio-4-ethylisobiuret, 42, 89 l-Phenyl-2-thio-4-methylisobiuret, 42, 87... 

A. l-Phenyl-2-thio-4-methylisobiuret. Into a 500-ml. three-necked flask fitted with a Hershberg stirrer 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 ISO 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. 

B. l-Phenyl-2-thiobiuret. A solution of 20.9 g. (0.1 mole) of l-phenyl-2-thio-4-methylisobiuret in 200 ml. of hot absolute ethanol is treated with 40 ml. of concentrated hydrochloric add, and the clear liquid is heated under reflux until no more methyl chloride is evolved (6-12 minutes. Note 4). The resulting solution is stirred into 2 1. of water, and the separated crystalline predp-itate is collected after storage at 0° for at least 24 hours. The dried product is dissolved in boiling absolute ethanol (5-6 ml. per g.), then the hot solution is quickly filtered by light suction and diluted with half its volume of petroleum ether (b.p. 60-80°). The separated l-phenyl-2-thiobiuret is collected by suction filtration after storage for 12 hours at room temperature, and rinsed-with small portions of a mixture of equal volumes of ethanol and petroleum ether. The yield of product, m.p. 159-161° (NoteS), is 8.8-10.5 g. (45-54%) (Note 6). 

Phenyl-2-thiobiuret has been prepared by the pyrolysis, at 75-90°, of l-phenyl-2-thio-4-methylisobiuret hydrochloride,4 and by the condensation of carbamyl isothiocyanate with aniline.6 The method here described, which is based on the former method, is regarded as most convenient. A comprehensive review of syntheses of biurets, thiobiurets, and dithiobiurets is available.6... 

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