B.
Guanidoacetic acid. This reaction should be carried out in a
well-ventilated hood, as considerable amounts of
ethyl mercaptan are evolved. In a
1-l. Erlenmeyer flask is placed
92.5 g. (0.50) mole of S-ethylthiourea hydrobromide. The flask is immersed in an
ice bath, and
252 ml. of 2 N sodium hydroxide solution is added. A hot (80+°) solution of
41 g. of glycine in 90 ml. of water is added rapidly. When the temperature reaches 25° (Note
6), the flask is removed from the ice water. After about 30 minutes crystallization begins; then approximately
100 ml. of ether is added, and the mixture is left in the hood overnight (Note
7). The mixture is then chilled for 2 hours in an
ice bath, the
ether layer is decanted, and the solid is filtered with suction. The crystals are washed on the funnel successively with two 20-ml. portions of ice water (Note
8), two
150-ml. portions of 95% ethanol, and two
150-ml. portions of ether. The yield of air-dried
guanidoacetic acid is
47–53 g. (
80–90%). This product is pure enough for most purposes (Note
9); it melts with decomposition at
280–284°.