Org. Synth. 1926, 6, 20
Submitted by R. Lespieau and M. Bourguel.
Checked by Roger Adams and M. M. Brubaker.
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 preparation of cyclohexylmagnesium chloride
is described on p. 188
. The solution may be standardized by titrating against 0.5 N hydrochloric acid
, and exactly one mole equivalent is used in the preparation. Five cubic centimeters of cyclohexylmagnesium bromide
solution is slowly added to 20 cc. of water, an excess of the standard acid is added, and the excess acid titrated with sodium hydroxide
. If 85 g. (3.5 atoms) of magnesium
, 1 l. of dry ether
, and 571 g. of cyclohexyl bromide (3.5 moles)
are used, a solution results which is about 2 molar.
Excess of Grignard reagent may be employed and the same yield obtained, so that the titration is an aid to conserving Grignard reagent. About an 80
per cent yield of cyclohexylmagnesium bromide
from cyclohexyl bromide
can generally be depended upon. Superior yields for both cyclohexylmagnesium chloride and bromide
have been reported.1
Directions for the preparation of cyclohexylmagnesium chloride
in superior yields are given in the preparation of cyclohexylcarbinol
on p. 188
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.
By a similar procedure2 benzylmagnesium chloride
in about 45
per cent yield, b.p. 119° /20 mm.
; and heptylmagnesium bromide
per cent yields, b.p. 76–77° /3 mm.
can be prepared by the action of cyclohexylmagnesium bromide
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
cyclohexylmagnesium chloride and bromide
calcium chloride (10043-52-4)
hydrochloric acid (7647-01-0)
sodium hydroxide (1310-73-2)
Propene, 2-bromo-3-cyclohexyl- (53608-85-8)
Cyclohexyl bromide (108-85-0)
magnesium bromide (7789-48-2)
benzylmagnesium chloride (6921-34-2)
heptylmagnesium bromide (13125-66-1)
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