In a
500-ml. three-necked flask, equipped with a stirrer, a
reflux condenser, and a
dropping funnel, is placed
140 ml. (34 g.; 2 moles of ammonia) of concentrated ammonium hydroxide solution, and
95 g. (1.3 moles) of methyl isothiocyanate (p. 599), b.p.
115–121°, is added, with stirring, over a period of 1 hour (Note
1). After the addition has been completed, the condenser is removed and the solution is heated on a
water bath for 30 minutes to remove excess
ammonia. The solution is then boiled with
2 g. of Norit and filtered, and the filtrate is chilled in an
ice bath. The
methylthiourea crystallizes as a colorless, compact, solid mass, which is collected on a filter, washed three times with 25-ml. portions of ice water, and dried. The first crop of crystals weighs
65–75 g. A second crop amounting to
15–20 g. is obtained by concentrating the mother liquor and washings to a volume of 75 ml. and again chilling in the ice bath. The total yield of
methylthiourea, m.p.
119–120.5° (Note
2), is
85–95 g. (
74–81%) (Note
3) and (Note
4).