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Diethyl sulfide: Finely powdered thiourea (86g, 1.1 moles) is boiled with ethanol (50ml) and
ethyl bromide (109 g, 1 mole) under reflux for 6 h; towards the end of this time the thiourea
dissolves. The solution is evaporated in a vacuum on the water-bath and, without waiting
for the residue to crystallize, water (100 ml) is added through a dropping funnel, followed
by a solution of sodium or potassium hydroxide (4 moles) in water (200 ml) during 10 min
with stirring. This mixture is boiled for an hour under a very efficient reflux condenser; it
is then cooled, ethyl bromide (164 g, 1.5 moles) is dropped in during 30min, and gentle boiling is
renewed for 5 h. The reflux condenser is replaced by a descending condenser, and the mixture
is distilled until 1 L of distillate has collected; the volume of liquid in the distillation flask
must be kept constant by continual addition of water, so as to avoid separation of potassium
or sodium bromide. The distillate is acidified, with cooling, by concentrated hydrochloric
acid and again similarly distilled (1 L of distillate). The diethyl sulfide is separated in a separatory
funnel, washed with 10% sodium hydroxide solution and then with water, dried over calcium
chloride, and distilled through a 20-cm Vigreux column, then having b.p. 90-92° (65 % yield).
Dimethyl and dipropyl sulfide are obtained similarly in 60% yield.
Mixed sulfides can be prepared by reaction of alkyl or aryl halides with
thiols or better, because of their greater reactivity, with thiolates:
RSNa + R'Cl -> RSR' + NaCl
The reaction is most satisfactory with alkyl and aryl bromides, since the chlorides
are mostly insufficiently reactive. |