A
1-l. three-necked, round-bottomed flask equipped with a
mechanical stirrer, a
gas-inlet tube, and a
dropping funnel is charged with
200 ml. of pyridine (Note
1) and
9.9 g. (0.10 mole) of copper(I) chloride (Note
2) which partially dissolves in
pyridine, forming a yellow suspension (Note
3).
Oxygen is bubbled into the suspension rapidly for 10 minutes; the suspension changes into a deep-green turbid solution (Note
4). A solution of
27 g. (0.25 mole) of 1,2-benzenediamine (Note
5) in
300 ml. of pyridine is added slowly from the dropping funnel during 2 hours, while vigorous stirring and bubbling of
oxygen are continued (Note
6), (Note
7). The reaction mixture is transferred to a 1-l., round-bottomed flask, and
pyridine is removed under reduced pressure (20 mm.) using a
rotary evaporator until a deep-green solid residue is obtained, to which
400 ml. of 6 N hydrochloric acid and
400 ml. of dichloromethane are added. The mixture is shaken until the solid is dissolved, and the lower layer is separated (Note
8). The upper layer is extracted with three
100-ml. portions of dichloromethane. The combined
dichloromethane solution is washed with
100 ml. of 5% aqueous sodium hydrogen carbonate, dried over anhydrous
sodium sulfate, and evaporated. The brown residue is dissolved in
600 ml. of warm benzene, and the solution is filtered through filter paper. When the
benzene is evaporated,
23–24 g. (
88–93%) of crude product is obtained as a brownish solid, which is recrystallized twice from
methanol (7 ml. for 1 g. of the crude material), yielding
19–20 g. (
73–77%) of
(Z,Z)-2,4-hexadienedinitrile as colorless needles, m.p.
128–129° (Note
9).