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.
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).