Organic Syntheses, CV 5, 1145
Submitted by Edward E. Schweizer and Robert D. Bach
1.
Checked by François X. Garneau and Peter Yates.
1. Procedure
Caution! Because
phenol and its solutions are corrosive, rubber gloves should be used in the following operations. The product,
vinyl triphenylphosphonium bromide, has been found to induce a sneezing, allergic reaction and contact with it should be avoided.
In a
1-l. three-necked flask is placed
1 lb. of reagent grade phenol (Note
1),
100 g. (0.50 mole) of β-bromophenetole, and
131 g. (0.50 mole) of triphenylphosphine (Note
2). The flask is equipped with a
sealed stirrer, a
thermometer, and a
reflux condenser fitted with a
calcium chloride drying tube. The mixture is stirred and heated to 90° ± 3° (Note
3) and kept at this temperature for 48 hours.
The solution is cooled to room temperature and added slowly (during 45 minutes) from a
dropping funnel to vigorously stirred anhydrous
ether (3 l.) in a
4-l. beaker. Material that adheres to the sides of the beaker is scraped down with a
long steel spatula, and the mixture is filtered by suction. The solid product is transferred into a second
3-l. portion of anhydrous ether, and the mixture is stirred vigorously for 15 minutes and filtered by suction. The product is washed with three
250-ml. portions of warm anhydrous ether.
The white crystalline residue of crude
phenoxyethyltriphenylphosphonium bromide (Note
4) is placed in a
3-l. two-necked flask equipped with a sealed stirrer and a reflux condenser fitted with a calcium chloride drying tube.
Reagent grade (Note 5) ethyl acetate (1.5 l.) is added, and the solution is stirred under reflux for 24 hours. The mixture is cooled to room temperature, and the
ethyl acetate layer is decanted (or filtered if the salt is crystalline). This procedure is repeated until the filtered salt,
vinyl triphenylphosphonium bromide, melts at
186° and higher (Note
6).
After the final filtration the product is washed with two
100-ml. portions of ethyl acetate and two
100-ml. portions of anhydrous ether and dried for 24 hours at 80°. The dried, analytically pure
vinyl triphenylphosphonium bromide, m.p.
186–190°, weighs
122–158 g. (
66–86%).
2. Notes
1. The checkers found that it was important to use
phenol free of colored impurities; in a run in which
phenol, m.p.
39.5–41°, with a slight rose tinge was used the yield of product was reduced to
56%.
2. The
β-bromophenetole was obtained from Aldrich Chemical Co.; the
triphenylphosphine was obtained from M and T Chemicals, Inc., or Carlisle Chemical Works, Reading, Ohio, and recrystallized once from anhydrous
ether (with filtration).
3. It is important that the temperature does not rise above 95°. There is a slight exotherm on initial heating that may necessitate the removal of the heating mantle in order to maintain a temperature below 95°.
4. Pure samples of this material may be obtained by using
acetic acid as solvent instead of
phenol.
2
5. Because the vinyl salt reacts with
ethanol, and decomposition of the phenoxyethyl precursor is inhibited by
acetic acid,
2 reagent grade ethyl acetate is recommended.
6. Four treatments have always been necessary. The residue has always crystallized on cooling after the third treatment.
3. Discussion
4. Merits of the Preparation
This salt has been used as a general reagent for the preparation of a large number of heterocyclic and carbocyclic systems.
4,5,6,7,8,9,10,11,12,13,14,15,16,17 A variety of salts of type XCH
2CH
2P
+(C
6H
5)
3Br
− has been prepared from the vinyl salt by treatment with alcohols,
thiophenol, and
diethylamine.
2
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