The apparatus, consisting of a
1-l. three-necked flask, fitted with a
glycerol-sealed mechanical stirrer, two inlet tubes (10-mm. bore) extending nearly to the blades of the stirrer, and an outlet tube (Note
1), is set up in a good
hood. Into a solution of
91 g. (0.5 mole) of N-methyl-1-naphthylcyanamide (p. 608) in
350 ml. of absolute ethanol, mechanically stirred and cooled by immersion of the flask in a
water bath maintained at 20–25°,
ammonia is bubbled at a moderate rate. After 5 minutes,
hydrogen sulfide (Note
2) is passed into the solution at about the same rate. The introduction of
ammonia is continued for 1.5 hours;
hydrogen sulfide is passed into the mixture an additional 30 minutes. A white solid begins to separate soon after the first addition of
hydrogen sulfide. After the mixture is chilled in an
ice-salt bath, it is filtered. The solid is suspended in 350 ml. of cold water, again separated by filtration, and finally washed with two 100-ml. portions of water, then with two
100-ml. portions of methanol, and dried. The yield of
1-methyl-1-(1-naphthyl)-2-thiourea, m.p.
168–170° (Note
3), amounts to
89–97 g. (
82–90%); this material is suitable for most purposes.