Org. Synth. 1959, 39, 56
Submitted by Lars Skattebøl, E. R. H. Jones, and Mark C. Whiting1
Checked by Melvin S. Newman and Raymond E. Dessy.
A. Ethynylmagnesium bromide. A 500-ml. three-necked flask, equipped with a sealed mechanical stirrer, a reflux condenser, and a pressure-equalized dropping funnel, is arranged for carrying out a reaction in an atmosphere of nitrogen by fitting into the top of the condenser a T-tube attached to a low-pressure supply of nitrogen and to a mercury bubbler. For later use there is also prepared a dry 1-l. three-necked flask equipped with a sealed mechanical stirrer, a gas inlet tube which will dip below the surface of 200 ml. of liquid in the flask, a 500-ml. dropping funnel, and a gas outlet protected by a calcium chloride drying tube.
The 500-ml. flask is dried by warming with a soft flame as a slow stream of nitrogen is passed through the system. A solution of ethylmagnesium bromide is prepared in this flask from 12 g. (0.5 g. atom) of magnesium turnings, 60 g. (0.55 mole) of ethyl bromide (dried over calcium chloride), and 300 ml. of tetrahydrofuran (Note 1) and (Note 2).
After the preparation of ethylmagnesium bromide is completed, the separatory funnel is replaced by a bent tube which reaches the bottom of the flask and is bent at the outer end for downward delivery (Note 3). The warm (40–50°) solution is forced under nitrogen pressure (by carefully pinching off the tube to the mercury bubbler) into the 500-ml. separatory funnel which has been prepared for attachment to the 1-l. flask. After all the solution has passed into the separatory funnel, nitrogen flow is allowed to continue briefly in order to displace the air above the solution, then the funnel is stoppered loosely and attached to the 1-l. flask. Two hundred milliliters of purified tetrahydrofuran is now placed in the flask, acetylene (Note 4) is introduced through the gas-inlet tube at the rate of 15–20 l. per hour, and the stirrer is started. After 5 minutes, about 5 ml. of the solution of ethylmagnesium bromide is added in 1 portion. Almost at once, there appears a froth of ethane which is easily distinguishable from the larger bubbles of acetylene. When the frothing subsides, portionwise addition of the ethylmagnesium bromide solution is continued until the total solution has been added. This requires about 3 hours, and the temperature of the reaction rises 5–10° above room temperature. The solution of ethynylmagnesium bromide is homogeneous at 30° (Note 5).
B. 1-Phenyl-1-penten-4-yn-3-ol. The stirred solution of ethynylmagnesium bromide is cooled in ice water as there is added dropwise during about 45 minutes a solution of 47.5 g. (0.36 mole) of freshly distilled cinnamaldehyde (Note 6) in 50 ml. of purified tetrahydrofuran. After addition is complete, stirring is continued overnight as the solution is allowed to warm to room temperature. The brown homogeneous reaction mixture is added carefully to 1.5 l. of cooled saturated ammonium chloride solution, then the aqueous phase is extracted with three 250-ml. portions of ether. The ether extracts are combined with the tetrahydrofuran solution and dried over anhydrous magnesium sulfate. After evaporation of the solvent, the product is distilled (Note 7) at a pressure of about 0.1 mm., with the heating bath at about 90°. The distillate, which solidifies on cooling, is crystallized from petroleum ether (b.p. 40–60°) to yield 33–39 g. (58–69%) of the unsaturated alcohol of m.p. 67–68° (Note 8).
If less solvent is used, the ethylmagnesium bromide
may crystallize on cooling.
is substituted for tetrahydrofuran
in this preparation, the acetylenic glycol is the sole product. The submitters purified the tetrahydrofuran
by shaking with potassium hydroxide
pellets, heating under reflux with sodium metal
, and finally distilling. They report that heating under reflux with sodium diphenylketyl
gives a better sample of tetrahydrofuran
, but that this does not improve the yield.
The checkers purified the solvent by shaking with potassium hydroxide, distilling from lithium aluminum hydride, then storing over sodium wire.
It is advisable to prepare the delivery tube prior to its need.
The submitters purified the acetylene
by passing it through a trap
cooled to −80°, then through concentrated sulfuric acid
, and finally through soda-lime
. The checkers purified the acetylene
by passing it first through a tower of 10-mesh alumina
, then through concentrated sulfuric acid
No outside cooling is employed during the preparation of ethynylmagnesium bromide
. If this solution of ethynylmagnesium bromide
is cooled to 0°, a crystalline complex separates. If part of the solvent is evaporated, even at 40° under reduced pressure, there occurs disproportionation to acetylene
and the bisbromomagnesium derivative.
Methyl ethyl ketone
, and acrolein
react similarly with ethynylmagnesium bromide
. The respective yields of acetylenic alcohols are 69%, 84%, and 40%.
The submitters used a still of the evaporative type, such as a Hickman still. The checkers used a similar still modified to include a magnetic stirring bar
. This modification greatly decreases the time required for removal of the last traces of solvent, minimizes the danger of bumping just before evaporative distillation occurs, and increases the rate of distillation of the product.
The checkers report yields as high as 84%
and believe that the use of magnetic stirring in the Hickman still is responsible for the higher yield.
The preparation of ethynylmagnesium bromide
has been described;2,3
however, the subsequent history of the compound has been controversial. The submitters have been unable to prepare ethynylcarbinols by the earlier procedures.
has been prepared in liquid ammonia
and sodium acetylide
and from the sodium bisulfite compound of cinnamaldehyde
and sodium acetylide
The present procedure has been published.6
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
sodium bisulfite compound of cinnamaldehyde
calcium chloride (10043-52-4)
sulfuric acid (7664-93-9)
ammonium chloride (12125-02-9)
magnesium turnings (7439-95-4)
Ethyl bromide (74-96-4)
potassium hydroxide (1310-58-3)
sodium wire (13966-32-0)
ethylmagnesium bromide (925-90-6)
magnesium sulfate (7487-88-9)
methyl ethyl ketone (78-93-3)
lithium aluminum hydride (16853-85-3)
1-Penten-4-yn-3-ol, 1-phenyl- (14604-31-0)
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