A Publication
of Reliable Methods
for the Preparation
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Annual Volume
Org. Synth. 1937, 17, 7
DOI: 10.15227/orgsyn.017.0007
[Caproic acid, ε-amino-]
Submitted by J. C. Eck
Checked by Louis F. Fieser and C. H. Fisher.
1. Procedure
In a 500-cc. round-bottomed flask, 50 g. (0.44 mole) of 2-ketohexamethylenimine (p. 371) is added to a solution of 45 cc. of concentrated hydrochloric acid (sp. gr. 1.19) in 150 cc. of water. The solution is boiled for about one hour until it becomes clear (Note 1) and evaporated to dryness under reduced pressure on a steam bath.
The resulting ε-aminocaproic acid hydrochloride is converted to the free acid by a procedure similar to that used in the preparation of dl-alanine (Org. Syn. Coll. Vol. I, 1941, 21). The hydrochloride is dissolved in 1 l. of water in a 1.5-l. beaker and treated successively with 50 g. of powdered litharge, 25 g. of powdered litharge, 5 g. of freshly precipitated lead hydroxide, 25 g. of powdered silver oxide (Note 2), and, finally, hydrogen sulfide. During this procedure, the original volume is maintained by the addition of small amounts of water.
After the complete removal of halogen and metallic ions, the solution is concentrated to a volume of about 100 cc., and 300 cc. of absolute alcohol is added. Then the amino acid is precipitated by slowly adding 500 cc. of ether with stirring and cooling.
The resulting ε-aminocaproic acid is collected on a suction filter and dried in a desiccator. The yield of ε-aminocaproic acid melting at 201–203° is 52.5–53.5 g. (90–92 per cent of the theoretical amount).
2. Notes
1. This indicates that the hydrolysis is complete.
2. The exact amount of silver oxide required may be determined by titrating a sample of the solution with silver nitrate by the Volhard method.
3. Discussion
ε-Aminocaproic acid has been prepared by the hydrolysis of ε-benzoylaminocapronitrile,1 by the hydrolysis of ethyl δ-phthalimidobutylmalonate,2 and from cyclohexanone oxime by rearrangement and hydrolysis.3
This preparation is referenced from:

References and Notes
  1. von Braun and Steindorff, Ber. 38, 176 (1905); von Braun, ibid. 40, 1839 (1907); Ruzicka and Hugoson, Helv. Chim. Acta 4, 479 (1921); Marvel, MacCorquodale, Kendall, and Lazier, J. Am. Chem. Soc. 46, 2838 (1924).
  2. Gabriel and Maass, Ber. 32, 1266 (1899).
  3. Wallach, Ann. 312, 188 (1900); Eck and Marvel, J. Biol. Chem. 106, 387 (1934).

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

alcohol (64-17-5)

hydrochloric acid (7647-01-0)

ether (60-29-7)

lead hydroxide

silver oxide (20667-12-3)

hydrogen sulfide (7783-06-4)

silver nitrate (7761-88-8)

Caproic acid, ε-amino- (60-32-2)

2-Ketohexamethylenimine (105-60-2)

ε-aminocaproic acid hydrochloride


ethyl δ-phthalimidobutylmalonate

Cyclohexanone oxime (100-64-1)

DL-Alanine (302-72-7)