Organic Syntheses, CV 5, 985
Submitted by Tod W. Campbell and Richard N. McDonald
1.
Checked by Virgil Boekelheide and Richard E. Partch.
1. Procedure
B.
1,4-Bis-(4-phenylbutadienyl)benzene. To a solution of
70 g. (0.10 mole) of p-xylylene-bis(triphenylphosphonium chloride) and
35 g. (0.26 mole) of cinnamaldehyde in
250 ml. of ethanol (Note
4) is added a solution of
0.25M lithium ethoxide in
ethanol (Note
5). After being allowed to stand overnight at room temperature the yellow solid is collected by filtration, washed with
300 ml. of 60% ethanol, and dried in a vacuum oven at 20 mm. and 70°. The dry weight is
29–32 g. (
87–95%). The solid is then dissolved in the minimum amount
(about 2 1.) of boiling xylene, treated with decolorizing charcoal, and filtered. The filtrate is reduced in volume to about 1.2 1. and digested at the boiling point with a trace of
iodine for 3 hours (Note
6). After the solution has stood overnight at room temperature, the yellow plates are collected by filtration, washed with
benzene, and dried in a vacuum oven at 20 mm. pressure at 70°. The weight of crystals, m.p.
285–287° (Note
7), is
23–25 g. (
69–75%).
C.
p-Quinquephenyl. A mixture of
3.40 g. (0.020 mole) of diethyl acetylenedicarboxylate2 and
3.34 g. (0.010 mole) of 1,4-bis-(4-phenylbutadienyl)benzene is refluxed with
20 ml. of o-dichlorobenzene for 3 hours. It is allowed to cool to about 80°, then
100 ml. of ethanol and
5 g. of potassium hydroxide are added, and the mixture is refluxed for about 2 hours. The solvent is evaporated on a
steam bath under a
nitrogen atmosphere (Note
8), and the damp solid is extracted with 200 ml. of water. The intense yellow or yellow-orange aqueous layer is filtered, then extracted twice with
75-ml. portions of ether, charcoal is added and then filtered to separate water-insoluble matter. The filtrate is just neutralized with dilute
hydrochloric acid (Note
9) and then made basic with
5 g. of sodium carbonate. To this is added a solution of
30 g. of potassium ferricyanide in 200 ml. of water. The mixture rapidly becomes milky and is allowed to stand overnight (Note
10). The suspended solid is centrifuged and washed with water twice by centrifugation. It is dried in a vacuum oven to give
3.1–4.2 g. of a green-tinged solid (Note
11). The combined material from five runs (
18 g.) is sublimed to give
10 g. (
52%) of pure
quinquephenyl, m.p.
385–390°. This can be recrystallized from
dimethylsulfoxide to give well-defined leaflets.
2. Notes
2. A sample of this compound was obtained from Hooker Electrochemical Co. and used without further purification.
3. The salt begins to precipitate after about 30 minutes.
4. Commercial anhydrous
ethanol was used throughout.
6. After the volume is reduced, a small crystal of
iodine is added whereupon large yellow leaflets of product begin to separate.
8.
Nitrogen is used both for rapid removal of the solvent and to maintain an inert atmosphere.
9. The acid is added slowly with stirring until a trace of permanent precipitate is formed.
10. All the steps to this point can be completed in 1 day.
3. Discussion
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