Org. Synth. 1926, 6, 20
DOI: 10.15227/orgsyn.006.0020
3-CYCLOHEXYL-2-BROMOPROPENE
[Propene, 2-bromo-3-cyclohexyl-]
Submitted by R. Lespieau and M. Bourguel.
Checked by Roger Adams and M. M. Brubaker.
1. Procedure
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 may separate.
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. (
60.5–64 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.
2. Notes
1.
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 and
magnesium 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.
2.
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).
3.
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.
4.
By a similar procedure
2 benzylmagnesium chloride and
2,3-dibromopropene give
4-phenyl-2-bromobutene in about
45 per cent yield, b.p.
119° /20 mm.; and
heptylmagnesium bromide and
2,3-dibromopropene give
2-bromodecene in
60–65 per cent yields, b.p.
76–77° /3 mm.
3. Discussion
3-Cyclohexyl-2-bromopropene can be prepared by the action of
cyclohexylmagnesium bromide on
2,3-dibromopropene3
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
cyclohexylmagnesium chloride and bromide
calcium chloride (10043-52-4)
hydrochloric acid (7647-01-0)
ether (60-29-7)
sodium hydroxide (1310-73-2)
magnesium (7439-95-4)
3-Cyclohexyl-2-bromopropene,
Propene, 2-bromo-3-cyclohexyl- (53608-85-8)
2,3-Dibromopropene (513-31-5)
cyclohexylmagnesium bromide
Cyclohexyl bromide (108-85-0)
magnesium bromide (7789-48-2)
dibromopropene (13195-80-7)
cyclohexylbromopropene
cyclohexylmagnesium chloride
Cyclohexylcarbinol (100-49-2)
benzylmagnesium chloride (6921-34-2)
4-phenyl-2-bromobutene
heptylmagnesium bromide (13125-66-1)
2-bromodecene
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