Org. Synth. 1967, 47, 31
DOI: 10.15227/orgsyn.047.0031
1,3-CYCLOHEXADIENE
Submitted by John P. Schaefer and Leland Endres
1.
Checked by R. J. Crawford and Peter Yates.
1. Procedure
In a 3-l. three-necked, round-bottomed flask fitted with a mechanical stirrer and set up for a simple vacuum distillation are placed 500 ml. of triethylene glycol dimethyl ether (Note 1) and 300 ml. of isopropyl alcohol. Mechanical stirring is started, and 53.5 g. (2.23 moles) of sodium hydride in a mineral oil suspension is added in small portions. After the addition is complete, the remaining neck of the flask is fitted with a Y-tube to which is connected a two-holed rubber stopper containing a thermometer which reaches into the flask below the liquid level and a piece of glass tubing which is connected to a nitrogen tank. A pressure-equalizing dropping funnel containing 242 g. (1.00 mole) of 1,2-dibromocyclohexane (Note 2) is placed in the other arm of the Y-tube.
The temperature of the reaction flask is raised to 100–110°, and the receiving flask is cooled in a dry ice-isopropyl alcohol bath as a rapid stream of nitrogen is passed through the system. After most of the isopropyl alcohol has been removed by distillation (Note 3), the receiver is changed, and the system is evacuated by a water aspirator (Note 4). Dropwise addition of 1,2-dibromocyclohexane is begun, and the rate of addition is adjusted so that the temperature of the reaction mixture is maintained at 100–110° without external heating. The addition requires about 30 minutes; the reaction is terminated when distillation becomes very slow.
The distillate is washed four times with 200-ml. portions of water, and the organic layer is dried with anhydrous magnesium sulfate. The yield of 1,3-cyclohexadiene is 56 g. (70%) (Note 5). The diene can be separated from higher-boiling contaminants by a simple distillation at atmospheric pressure under nitrogen; b.p. 78–80°, yield 28–32 g. (35–40%) (Note 6).
2. Notes
1.
1,2-Bis(methoxyethoxy)ethane (triethylene glycol dimethyl ether) was obtained from Matheson, Coleman and Bell and used without further purification.
2.
The
1,2-dibromocyclohexane was prepared by the method of Snyder and Brooks.
2 If the
cyclohexene is cooled to
ca. −30° with a dry ice-isopropyl alcohol bath and the
bromine is not diluted, it is possible to run this preparation on a threefold scale in one-third of the recorded time. The product was always purified by the recommended procedure.
3.
If the flow of
nitrogen is rapid, the distillation can be completed in about 1 hour; otherwise the distillation is very slow.
4.
A
dry ice-isopropyl alcohol trap was inserted before the aspirator to catch any uncondensed product. The checkers also inserted a manometer between this trap and the aspirator, and maintained the pressure during the reaction at 130–170 mm. by careful adjustment of the regulator valve of the nitrogen cylinder.
5.
If the temperature rises too high or the vacuum is not sufficient to flash out the diene as it forms, the product will be contaminated with small amounts of
cyclohexene, benzene, and 1,4-cyclohexadiene.
6.
The checkers found that distillation without the use of a
nitrogen atmosphere gave
43–44 g. (
54–55%) of product, b.p.
80–83°, of excellent purity as shown by n.m.r. spectroscopy.
3. Discussion
1,3-Cyclohexadiene has been prepared by dehydration of
cyclohexen-3-ol,
3 by pyrolysis at 540° of the
diacetate of cyclohexane-1,2-diol,
4 by dehydrobromination with
quinoline of 3-bromocyclohexene,
5 by treating the
ethyl ether of cyclohexen-3-ol with
potassium bisulfate,
6,7 by heating
cyclohexene oxide with
phthalic anhydride,
8 by treating
cyclohexane-1,2-diol with concentrated
sulfuric acid,
9 by treatment of
1,2-dibromocyclohexane with
tributylamine,
10 with
sodium hydroxide in
ethylene glycol,
10 and with
quinoline,
6 and by treatment of
3,6-dibromo-cyclohexene with
sodium.
6
4. Merits of the Preparation
Because of its convenience and simplicity this procedure is the method of choice for laboratory preparation of
1,3-cyclohexadiene. This olefin is an intermediate of some importance because it offers a route via the Diels-Alder reaction to a variety of bicyclic compounds.
4,7,10This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
diacetate of cyclohexane-1,2-diol
quinoline of 3-bromocyclohexene
sulfuric acid (7664-93-9)
Benzene (71-43-2)
sodium hydroxide (1310-73-2)
Cyclohexene (110-83-8)
bromine (7726-95-6)
nitrogen (7727-37-9)
phthalic anhydride (85-44-9)
potassium bisulfate (7646-93-7)
sodium (13966-32-0)
isopropyl alcohol (67-63-0)
ethylene glycol (107-21-1)
Cyclohexene oxide (286-20-4)
Quinoline (91-22-5)
magnesium sulfate (7487-88-9)
1,2-Dibromocyclohexane (5401-62-7)
cyclohexane-1,2-diol
sodium hydride (7646-69-7)
1,3-Cyclohexadiene (592-57-4)
triethylene glycol dimethyl ether,
1,2-Bis(methoxyethoxy)ethane (112-49-2)
1,4-cyclohexadiene
cyclohexen-3-ol
tributylamine (102-82-9)
3,6-dibromo-cyclohexene
ethyl ether of cyclohexen-3-ol
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