Org. Synth. 1960, 40, 41
DOI: 10.15227/orgsyn.040.0041
3-ETHOXY-2-CYCLOHEXENONE
[Dihydroresorcinol monoethyl ether]
Submitted by Walter F. Gannon and Herbert O. House
1.
Checked by William E. Parham, Wayland E. Noland, George Meisters, and Allan M. Huffman.
1. Procedure
In a 2-l. flask fitted with a total-reflux, variable-take-off distillation head is placed a solution of 53 g. (0.472 mole) of dihydroresorcinol (Note 1), 2.3 g. of p-toluenesulfonic acid monohydrate and 250 ml. of absolute ethanol in 900 ml. of benzene. The mixture is heated to boiling and the azeotrope composed of benzene, alcohol, and water is removed at the rate of 100 ml. per hour. When the temperature of the distilling vapor reaches 78° (Note 2), the distillation is stopped and the residual solution is washed with four 100-ml. portions of 10% aqueous sodium hydroxide which have been saturated with sodium chloride. The resulting organic solution is washed with successive 50-ml. portions of water until the aqueous washings are neutral and then concentrated under reduced pressure. The residual liquid is distilled under reduced pressure. The yield of 3-ethoxy-2-cyclohexenone (Note 3), b.p. 66–68.5°/0.4 mm. or 115–121°/11 mm., n29D 1.5015, is 46.6–49.9 g. (70–75%).
2. Notes
1.
The preparation of
dihydroresorcinol was described in an earlier volume of this series.
22.
This distillation requires 6–8 hours.
3.
The product may be analyzed by gas chromatography on an
8 mm. × 215 cm. column heated to 220–240° and packed with Dow-Corning Silicone Fluid No. 550 suspended on 50–80 mesh ground firebrick. The chromatogram obtained with this column exhibits a single major peak. The ultraviolet spectrum of an
ethanol solution of the product has a maxium at 250 mμ (ε = 17,200).
3. Discussion
3-Ethoxy-2-cyclohexenone has been prepared by reaction of the
silver salt of dihydroresorcinol with
ethyl iodide3 and by the reaction of
dihydroresorcinol with
ethyl orthoformate,
ethanol and
sulfuric acid.
4 The acid-catalyzed reaction of
dihydroresorcinol with
ethanol in
benzene solution utilized in this preparation is patterned after the procedure of Frank and Hall.
4,5
This procedure can also be used to prepare other 2-alkoxy-2-cyclohexenones. For example, it has been reported that
2-isobutoxy-2-cyclohexenone can be prepared easily in high yield (
91%) from
dihydroresorcinol and
isobutyl alcohol.
6 The use of
isobutyl alcohol7 often gives better yields of enol ethers.
8,94. Use of 3-Ethoxy-2-cyclohexenone
The 3-alkoxy-2-cyclohexenones are useful intermediates in the synthesis of certain cyclohexenones. The reduction of
3-ethoxy-2-cyclohexenone with
lithium aluminum hydride followed by hydrolysis and dehydration of the reduction product yields
2-cyclohexenone.
10 Similarly, the reaction of 3-alkoxy-2-cyclohexenones with organometallic reagents followed by hydrolysis and dehydration of the addition product affords a variety of 3-substituted 2-cyclohexenones.
3,5,6,8This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethanol (64-17-5)
sulfuric acid (7664-93-9)
Benzene (71-43-2)
sodium hydroxide (1310-73-2)
sodium chloride (7647-14-5)
Ethyl orthoformate
isobutyl alcohol (78-83-1)
Ethyl iodide (75-03-6)
lithium aluminum hydride (16853-85-3)
Dihydroresorcinol
2-Cyclohexenone (930-68-7)
3-Ethoxy-2-cyclohexenone,
Dihydroresorcinol monoethyl ether (5323-87-5)
2-isobutoxy-2-cyclohexenone
p-toluenesulfonic acid monohydrate (6192-52-5)
silver salt of dihydroresorcinol
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