Org. Synth. 1960, 40, 14
Submitted by Walter F. Gannon and Herbert O. House1
Checked by William E. Parham, Allan M. Huffman, George J. Meisters, and Wayland E. Noland.
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%).
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).
This addition requires approximately 1.5 hours.
The addition of water is accompanied by foaming, and care must be taken to avoid excessive loss of the solvent.
obtained by an ordinary distillation at this point is contaminated with lower-boiling impurities (see (Note 5)
), primarily ether
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
, 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).
has been prepared by dehydrohalogenation of 2-bromocyclohexanone
by the hydrolysis and oxidation of 3-chlorocyclohexene
by the dehydration of α-hydroxycyclohexanone
by the oxidation of cyclohexene
with chromic acid7
or hydrogen peroxide
in the presence of a vanadium
by the addition of acrolein
to ethyl acetoacetate
followed by cyclization, hydrolysis, and decarboxylation,9
by the reduction of N,N-dimethylaniline
in liquid ammonia
followed by hydrolysis,10
by the reduction of anisole
in liquid ammonia
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.12,13,14
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
sulfuric acid (7664-93-9)
sodium bicarbonate (144-55-8)
chromic acid (7738-94-5)
hydrogen peroxide (7722-84-1)
Ethyl acetoacetate (141-97-9)
magnesium sulfate (7487-88-9)
lithium aluminum hydride (16853-85-3)
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