Org. Synth. 1951, 31, 3
DOI: 10.15227/orgsyn.031.0003
δ-ACETYL-n-VALERIC ACID
[Heptanoic acid, 6-oxo-]
Submitted by J. R. Schaeffer and A. O. Snoddy
1.
Checked by Richard T. Arnold and H. W. Turner.
1. Procedure
A solution of
368 g. of 96% sulfuric acid in 664 ml. of water is cooled to room temperature and placed in a
3-l. three-necked flask provided with a mechanical stirrer, a thermometer, and a dropping funnel. To this acid solution is added
114 g. (1 mole) of 2-methylcyclohexanol (Note 1). A mixture of
220 g. (2.2 moles) of chromic oxide (Note 2) in
368 g. of 96% sulfuric acid and 664 ml. of water is added from the dropping funnel to the
2-methylcyclohexanol suspension at such a rate that the temperature of the mixture remains at 30 ± 2°
(Note 3). Good agitation and an
ice bath are necessary to control the temperature in this range. The mixture is stirred at 30 ± 2° for 1 hour and then at room temperature until all the
chromic oxide is consumed
(Note 4). The
sulfuric acid solution is extracted with
ether until the returns from the
ether extractions fall to an insignificant amount. Approximately 10 extractions with
200-ml. portions of ether are required
(Note 5). The
ether extracts are combined, and the
ether is removed by distillation on the
steam bath. The resulting crude
δ-acetyl-n-valeric acid is a yellow liquid with a sharp odor and amounts to about
130 g. The crude acid is purified by distillation through a
30-in. Vigreux column, using a variable take-off, a reflux ratio of 3:1, and a pressure of 1 mm. A fore-run of approximately
30 g. of material distilling up to
122°/1 mm. is obtained. The main fraction which distils at
122–123°/1 mm. is pure
δ-acetyl-n-valeric acid and amounts to
66–79 g. (
46–55%). The pure acid is a colorless crystalline hygroscopic solid which melts (sealed capillary) at
34–35° and is miscible with water in all proportions. The literature records the melting point of
δ-acetyl-n-valeric acid as ranging from
31° to 42°.2,3,4
2. Notes
1.
Eastman Kodak Company practical grade 2-methylcyclohexanol was used in this preparation.
2.
Technical grade chromic oxide (99.5% CrO3) in flake form was used.
3.
An
alcohol-Dry Ice bath is very convenient for this purpose; with this bath only about 45 minutes is needed for the addition of the
chromic oxide solution. A
water-ice bath can be used, but a longer time will be required for the addition of the
chromic oxide solution.
4.
The
chromic oxide content of the mixture at any time may be determined by titrating a test portion against standard
ferrous ammonium sulfate solution. If the mixture is allowed to stand overnight at room temperature without stirring, it will be free from
chromic oxide. A convenient procedure is to perform the oxidation in the afternoon and the extraction the next day.
5.
A
liquid-liquid continuous extractor is convenient for extracting the crude acid from the aqueous solution. With such apparatus, it is possible to extract all the crude
δ-acetyl-n-valeric acid from the aqueous acid in 6–8 hours.
6.
The fore-run and the still residue contain some
δ-acetyl-n-valeric acid. These fractions may be combined and redistilled to yield an additional
5–10% of
δ-acetyl-n-valeric acid, but the low cost of the starting materials and the ease of preparing the crude
δ-acetyl-n-valeric acid scarcely justify the labor unless a considerable number of batches are being prepared.
3. Discussion
δ-Acetyl-n-valeric acid has been prepared by the oxidation of
1-methylcyclohexene with
potassium permanganate;
5 by the oxidation of
2-methylcyclohexanone with
chromic oxide and
sulfuric acid,
6,7 with neutral
potassium permanganate,
8 and by air in the presence of
adipic acid and
manganese nitrate;
9 by the reaction of
methylzinc iodide on the
ethyl ester of adipic acid chloride, followed by saponification of the ester so obtained;
10 by the saponification of the
ethyl ester of diacetylvaleric acid;
2 by the hydrolysis of
ethyl α-acetyl-δ-cyanovalerate with boiling
20% hydrochloric acid;
3 by the permanganate oxidation of
1-methyl-1,2-cyclopentanediol;
11 and by the alkaline cleavage of
2-acetylcyclopentanone.
12
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethyl ester of adipic acid chloride
sulfuric acid (7664-93-9)
hydrochloric acid (7647-01-0)
ether (60-29-7)
Adipic acid (124-04-9)
potassium permanganate (7722-64-7)
ferrous ammonium sulfate (10045-89-3)
2-methylcyclohexanone (583-60-8)
Heptanoic acid, 6-oxo-,
δ-ACETYL-n-VALERIC ACID (3128-07-2)
2-methylcyclohexanol (583-59-5)
chromic oxide (1308-38-9)
1-methylcyclohexene
manganese nitrate (10377-66-9)
methylzinc iodide
ethyl α-acetyl-δ-cyanovalerate
1-methyl-1,2-cyclopentanediol
2-acetylcyclopentanone (1670-46-8)
ethyl ester of diacetylvaleric acid
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved