Checked by O. Aniline and K. B. Wiberg.
1. Procedure
In a dry
3-l. three-necked, round-bottomed flask fitted with an efficient reflux condenser, a stirrer, a Y-tube holding a 1-l. and a 250-ml. addition funnel, and protected from moisture by calcium chloride tubes is placed
5.76 g. (0.237 mole) of magnesium turnings barely covered by
anhydrous ether.
p-Bromotoluene (40 drops) and
ethyl bromide (20 drops) are added, and the reaction starts immediately.
p-Bromotoluene (35.0 g., 0.205 mole) in
200 ml. of anhydrous ether is added at such a rate that reflux is maintained. To the resultant solution of
p-methylphenylmagnesium bromide is added, over a 1-hour period, a solution of
25.4 g. (0.200 mole) of dichloroacetone in
200 ml. of anhydrous ether.
At the same time, in a separate
2-l. three-necked, round-bottomed flask equipped with reflux condenser, stirrer, and addition funnel,
ethylmagnesium bromide is prepared from
128.6 g. (1.18 moles) of ethyl bromide and
30 g. (1.23 moles) of magnesium in
800 ml. of anhydrous ether. When the reaction is complete, the addition funnel is replaced by a
rubber stopper containing a
short glass tube, and the
reflux condenser is replaced by an
exit tube lightly plugged with a small amount of glass wool. The Grignard reagent solution is forced, under mild
nitrogen pressure, through the glass wool plug into the 1-l. addition funnel (Note
1). In the 250-ml. addition funnel is placed a filtered solution of
2.5 g. (0.0154 mole) of anhydrous ferric chloride in
200 ml. of anhydrous ether. Stirring is resumed, and the two solutions are simultaneously added to the
dichloroacetone-
p-methylphenylmagnesium bromide solution over a 2-hour period (Note
2). Stirring is continued for an additional 14 hours under dry
nitrogen.
The reaction mixture is added to a slurry of 1500 g. of ice and
600 ml. of 2N hydrochloric acid saturated with
ammonium chloride. The ether layer is separated, and the aqueous layer is extracted three times with
200-ml. portions of ether. The combined organic layers are washed with three 200-ml. portions of water until a neutral reaction is obtained with litmus and the wash water is free of chloride. The solution is dried over
anhydrous magnesium sulfate and stored in a refrigerator. After evaporation of the
ether, the residue is distilled at a low pressure through a
short Vigreux column (Note
3). The fraction, b.p.
70–78° (0.4 mm.) (
oil bath 100–135°), is collected to give
15–17 g. (
51–57%) of the crude carbinol which crystallizes upon standing in an ice box. The product is recrystallized from
pentane (4 g. per g. of alcohol) in an ice-salt mixture to give the pure alcohol, m.p.
38–39°.
2. Notes
1. Since the ethyl Grignard reagent is used in large excess, no special precautions need to be taken in the transfer to prevent the loss of small amounts.
2. Large volumes of gas are generated, primarily
ethane and
ethylene, from the disproportionation of the ethyl radicals produced in the reaction of
ethylmagnesium bromide with
ferric chloride. The reaction should be carried out in an
efficient hood, or else a tube should be run from the top of the
reflux condenser to a
hood.
3. 1-Arylcyclopropanols readily rearrange to propiophenones under the influence of acids and bases. In carrying out the distillation, care must be taken that the apparatus is clean and neutral.
3. Discussion
4. Merits of the Preparation
The procedure can be adapted to the preparation, in comparable yield, of a variety of 1-substituted cyclopropanols, alkyl as well as aryl.
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