Organic Syntheses, CV 5, 499
Submitted by Richard N. McDonald and Tod W. Campbell
1.
Checked by M. S. Newman, R. Marshall, and W. N. White.
1. Procedure
A.
Triphenylcinnamylphosphonium chloride. A mixture of
40 g. (0.26 mole) of (3-chloropropenyl) benzene (Note
1) and
92 g. (0.35 mole) of triphenylphosphine (Note
2) in
500 ml. of xylene is heated at reflux for 12 hours with stirring. The mixture is allowed to cool to about 60°, and the colorless crystalline product is filtered, washed with
100 ml. of xylene, and dried in a
vacuum oven at about 20 mm. pressure and 60° to constant weight. The yield is
99–101 g. (
91–93%), m.p.
224–226° (Note
3).
B.
1,4-Diphenylbutadiene. To a solution of
60.0 g. (0.145 mole) of triphenylcinnamylphosphonium chloride and
16.4 g. (0.155 mole) of benzaldehyde in 200 ml. of ethanol (Note
4) is added
760 ml. of 0.2M lithium ethoxide in ethanol (Note
5) and (Note
6). After allowing this mixture to stand 30 minutes, 700 ml. of water is added (Note
7) and the colorless crystals are filtered, washed with
150 ml. of 60% ethanol, and dried in the vacuum oven at 65°. The yield of crystalline product, m.p.
153–156°, is
17.9–19.9 g. (
60–67%) (Note
8). The product is the
trans-trans isomer and is pure enough for most purposes (Note
9). Recrystallization from
cyclohexane gives a product with m.p.
154–156°.
2. Notes
1. Eastman Organic Chemicals, white label grade, used without purification.
2. Commercial
triphenylphosphine was used without further purification. Metal and Thermit Corp., Rahway, New Jersey, now offers this reagent for sale at a modest price.
3. The phosphonium salt can be recrystallized to analytical purity by dissolving in a small amount of boiling
ethanol, adding
ether at the boil until cloudy, and allowing the salt to crystallize in a
refrigerator.
4. Commercial anhydrous
ethanol was used throughout without further purification.
6. A transient orange color is immediately formed, and it is replaced by crystallization of the product in about 1 minute.
8. The yield can probably be increased by carrying out the reaction in an ether solvent with an alkyllithium as base, but the simplicity and relative ease of the conditions described appear to make the possible yield advantage secondary.
3. Discussion
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