A
200-ml. two-necked flask is fitted with an
efficient Dry Ice-isopropyl alcohol condenser connected to a
soda-lime tube, a
magnetic stirrer, and a
gas inlet tube.
Isopropyl alcohol and Dry Ice are added to the condenser while the flask and condenser are flushed with dry
nitrogen. The flask is immersed in a
Dry Ice-isopropyl alcohol bath, and a vigorous stream of dry
ammonia is introduced into the system. When about
80 ml. of liquid ammonia is condensed, the gas inlet tube is replaced with a
ground-glass stopper. The cooling bath is removed, stirring is started, and
5.1 g. (0.020 mole) of 1,2-bis(n-butylthio) benzene (Note
1) is quickly introduced (Note
2).
Sodium is now added in small pieces; the solution is allowed to decolorize before each successive piece is added. A
water bath is placed occasionally under the flask to ensure continuous ebullition of
ammonia. The blue color will persist for at least 15 minutes after
1.6 g. (0.070 g. atom) of sodium has been added. The excess
sodium is then destroyed by
cautious addition of
6 g. (0.11 mole) of ammonium chloride, with stirring. Cooling and stirring are stopped, and a slow stream of
argon is passed in for a period of about 12–15 hours. The white solid residue is transferred to a
beaker, and 300 g. of ice water is added, together with sufficient pellets of
sodium hydroxide to make the solution alkaline. The alkaline solution is then extracted twice with
ether and the
ether extracts discarded. The solution is then acidified to Congo red with cold
1:1 (by volume) hydrochloric acid and extracted three times with
ether. The
ether extracts are combined, washed with water, and dried over anhydrous
sodium sulfate. The
ether is evaporated and the
1,2-dimercaptobenzene is distilled under reduced pressure under an atmosphere of
nitrogen, giving a product which boils at
95°/5 mm. and usually solidifies after distillation (Note
3). The yield is
1.6–2.4 g. (
56–85%) (Note
4).