Org. Synth. 1960, 40, 14
DOI: 10.15227/orgsyn.040.0014
2-CYCLOHEXENONE
Submitted by Walter F. Gannon and Herbert O. House
1.
Checked by William E. Parham, Allan M. Huffman, George J. Meisters, and Wayland E. Noland.
1. Procedure
In a dry 500-ml. three-necked flask, equipped with a reflux condenser, a mechanical stirrer, and a dropping funnel and protected from atmospheric moisture with drying tubes, are placed 6.0 g. (0.16 mole) of lithium aluminum hydride and 200 ml. of anhydrous ether. A solution of 43 g. (0.307 mole) of 3-ethoxy-2-cyclohexenone (Note 1) in 50 ml. of anhydrous ether is added, dropwise and with stirring, to the reaction flask at a rate which maintains gentle refluxing of the solvent (Note 2). After the addition is complete, the reaction solution is boiled under reflux for an additional 30 minutes and then allowed to cool. The complex is hydrolyzed and the excess lithium aluminum hydride is destroyed by the cautious addition, dropwise and with stirring, of 15 ml. of water (Note 3). The resulting reaction mixture is poured into 500 ml. of cold aqueous 10% sulfuric acid. The ether layer which forms is separated, and the residual aqueous phase is extracted with three 300-ml. portions of ether. The combined ether solutions are washed successively with one 100-ml. portion of water and one 100-ml. portion of saturated, aqueous sodium bicarbonate solution and then dried over magnesium sulfate. The ether is removed by distillation through a 50-cm. Vigreux column, and the residue is distilled under reduced pressure through a 40-cm. spinning-band column (Note 4). The yield of 2-cyclohexenone (Note 5), b.p. 56–57.5°/10 mm. or 96–97°/72 mm., nD27 1.4858, is 18.2–22.1 g. (62–75%).
2. Notes
1.
The preparation of
3-ethoxy-2-cyclohexenone is described elsewhere in this volume.
2 (It has been reported that
3-isobutoxy-2-cyclohexenone can be prepared in somewhat higher yield than the 3-ethoxy compound by the same procedure and that the 3-isobutoxy compound is just as useful for the present preparation (private communication from D. A. H. Taylor).
2.
This addition requires approximately 1.5 hours.
3.
The addition of water is accompanied by foaming, and care must be taken to avoid excessive loss of the solvent.
4.
The
2-cyclohexenone obtained by an ordinary distillation at this point is contaminated with lower-boiling impurities (see
(Note 5)), primarily
ether and
ethanol.
5.
The purity of the
2-cyclohexenone may be assayed by gas chromatography on an
8 mm. × 215 cm. column heated to 125° and packed with di-(2-ethylhexyl) sebacate suspended on ground firebrick. This method of analysis indicates that the
3-cyclohexenone in the product amounts to no more than 3%. The fore-run from this fractional distillation contains substantial amounts of
2-cyclohexenone accompanied by
ether,
ethanol, and minor amounts of other lower-boiling impurities. Additional quantities of pure
2-cyclohexenone can be recovered by redistillation of this fore-run. The preparation of
2-cyclohexenone has been run on twice the scale described with no loss in yield. The ultraviolet spectrum of an ethanol solution of the 2-cyclohexenone obtained has a maximum at 226 mμ (ε = 10,400).
3. Discussion
2-Cyclohexenone has been prepared by dehydrohalogenation of
2-bromocyclohexanone,
3,4 by the hydrolysis and oxidation of
3-chlorocyclohexene,
5 by the dehydration of
α-hydroxycyclohexanone,
6 by the oxidation of
cyclohexene with
chromic acid7 or
hydrogen peroxide in the presence of a
vanadium catalyst,
8 by the addition of
acrolein to
ethyl acetoacetate followed by cyclization, hydrolysis, and decarboxylation,
9 by the reduction of
N,N-dimethylaniline with
sodium and
ethanol in
liquid ammonia followed by hydrolysis,
10 by the reduction of
anisole with
lithium in liquid
ammonia,
11 and by the reduction of 3-alkoxy-2-cyclohexanones with
lithium aluminum hydride followed by acid-catalyzed hydrolysis and rearrangement.
12
The procedure described illustrates a general method for the preparation of α,β-unsaturated aldehydes and ketones from the enol ethers of β-dicarbonyl compounds.
12,13,14This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethanol (64-17-5)
sulfuric acid (7664-93-9)
ammonia (7664-41-7)
ether (60-29-7)
Acrolein (107-02-8)
sodium bicarbonate (144-55-8)
Cyclohexene (110-83-8)
Anisole (100-66-3)
sodium (13966-32-0)
chromic acid (7738-94-5)
hydrogen peroxide (7722-84-1)
N,N-dimethylaniline (121-69-7)
Ethyl acetoacetate (141-97-9)
lithium (7439-93-2)
magnesium sulfate (7487-88-9)
Vanadium (7440-62-2)
lithium aluminum hydride (16853-85-3)
2-bromocyclohexanone
α-hydroxycyclohexanone
2-Cyclohexenone (930-68-7)
3-Ethoxy-2-cyclohexenone (5323-87-5)
3-isobutoxy-2-cyclohexenone
3-cyclohexenone
3-chlorocyclohexene
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