Organic Syntheses, CV 5, 297
Submitted by Nicholas J. Turro
1, Peter A. Leermakers
2, and George F. Vesley
2.
Checked by Alex G. Fallis and Peter Yates.
1. Procedure
A.
Dispiro[5.1.5.1]tetradecane-7,14-dione.
Cyclohexanecarbonyl chloride (Note 1) (30.0 g., 0.205 mole) and
250 ml. of dry benzene are placed in a
three-necked, round-bottomed flask equipped with a
stirrer,
condenser, and
dropping funnel. A
nitrogen atmosphere is maintained in the system. Dry
triethylamine (35.0 g., 0.35 mole) is slowly added, and the mixture is heated under reflux overnight. The amine hydrochloride is then filtered, and the filtrate is washed with dilute
hydrochloric acid and with water. Solvent is removed on a
steam bath, and the residue is recrystallized from
ligroin-ethanol; yield
11–13 g. (
49–58%), m.p.
161–62°.
B.
Cyclohexylidenecyclohexane. In a
Hanovia 450-watt immersion photochemical reactor (Note
2), equipped with a side arm attachment to monitor gas evolution, is placed
15 g. (0.068 mole) of dispiro[5.1.5.1]tetradecane-7,14-dione dissolved in
150 ml. of methylene chloride. The sample is irradiated, and
carbon monoxide starts to evolve rapidly after a few minutes. Irradiation is continued until gas evolution has ceased, usually about 8–10 hours (Note
3). After the irradiation most of the solvent is removed on a steam bath. The residual oil is transferred to a sublimator. The sublimator, with the cold finger removed, is placed in a
vacuum desiccator, and the system is evacuated to remove any remaining
methylene chloride. The semisolid residue is then sublimed at 45° (1 mm.) to yield
7 g. (
63%) of crude
cyclohexylidenecyclohexane. The product after recrystallization from
methanol weighs
5.5 g. (
49%), m.p.
53–54°.
2. Notes
2. The reactor, manufactured by the Hanovia Division of Engelhard Industries, consists of a water-jacketed Vycor well through which a stream of water is continuously passed. Since wavelengths shorter than 3000 Å are not needed, the immersion well may be made of Pyrex instead. Within the well is a No. 679A-36 450-watt medium-pressure mercury lamp, also manufactured by Hanovia, and a cylindrical Pyrex filter which surrounds the lamp. The well is placed in an appropriately shaped flask containing the solution to be irradiated. The flask is essentially cylindrical and is equipped with a side arm near the top through which gas can escape and be bubbled through a container of water. The flask is so designed that the liquid level is above the top of the lamp. The reaction vessel is quite similar to that shown in
fig. 1.htm (p. 65).
The same synthesis could be carried out in an ordinary flask using one or two sunlamps or sunlight, but the irradiation time would necessarily be much longer.
3. The system should be relatively free of
oxygen during irradiation.
Oxygen apparently combines with a photochemical intermediate to form
cyclohexanone.
3 Under the conditions recommended in the procedure,
oxygen is prevented from entering the system by the
water trap which also serves as a monitor for gas evolution.
3. Discussion
4. Merits of the Preparation
The most obvious features of this synthesis are its simplicity and overall yield, which appear to be superior to those of any other published report. An important merit lies in the generality of the reaction, and the fact that it is an example of a reasonably large-scale photochemical preparation.
Tetramethylethylene is readily produced from commercially available
tetramethyl-1,3-cyclobutanedione by an identical route.
7
This preparation is referenced from:
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