Organic Syntheses, Coll. Vol. 1, p.186 (1941); Vol. 6, p.20 (1926).
A 3-l. three-necked round-bottomed flask
is fitted with a mechanical stirrer
through a mercury seal
, a reflux condenser
and a 1-l. separatory funnel
. A mixture of 200 g. (1 mole) of 2,3-dibromopropene (p. 209)
and 200 cc. of dry ether
is added. The flask is now cooled in an ice bath
, the stirrer is started, and one molecular equivalent of cyclohexylmagnesium bromide, prepared from 31 g. (1.28 atoms) of magnesium, 204 g. (1.25 moles) of cyclohexyl bromide, and 400 cc. of dry ether (Note 1)
, is added at such a rate that the mixture refluxes gently (Note 2)
. The addition takes about one-half to three-quarters of an hour. Two layers are formed, and magnesium bromide
The stirring should be continued and the ice bath replaced by a hot-water bath
, and the mixture refluxed gently for two hours. The flask is again cooled, and 30 cc. of concentrated hydrochloric acid
in 350 cc. of water is added through the separatory funnel
. This should be added slowly as long as heat is evolved. The contents of the flask are then transferred to a separatory funnel, the ether
layer separated and dried over calcium chloride
The ether is distilled on a steam bath (Note 3)
and the residue fractionated under reduced pressure by means of a 20-cm. column (p. 130)
. After three fractionations, there is obtained 32–44 g.
of a product boiling up to 100° /25 mm.
, which is mainly unchanged dibromopropene
(b.p. 42–43° /18 mm.
), and 123–130 g.
per cent of the theoretical amount, not taking into account recovered dibromopropene
) of cyclohexylbromopropene (Note 4)
boiling at 100–105° /25 mm.
This material is satisfactory for most purposes. On redistillation it boils at 88–89° /14 mm.
The reaction is instantaneous and is not stopped by moderate cooling. The cooling may be dispensed with and the cyclohexylmagnesium bromide
added more slowly (two hours).
The ether solution may be added in several portions to a 500-cc. modified Claisen flask (p. 130)
and the ether
distilled after each addition.
This preparation is referenced from:
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