Org. Synth. 1925, 5, 9
DOI: 10.15227/orgsyn.005.0009
ADIPIC ACID
Submitted by B. A. Ellis
Checked by Roger Adams and C. D. Thompson.
1. Procedure
In a 5-l. round-bottomed flask fitted with a mechanical stirrer, a thermometer, and a 1-l. separatory funnel, is placed 2100 g. (16.6 moles) of 50 per cent nitric acid (sp. gr. 1.32) (Hood). The acid is heated nearly to boiling, and 1 g. of ammonium vanadate (Note 1) is added. The stirrer is started, and 500 g. (5 moles) of cyclohexanol (Note 2) is introduced slowly through the separatory funnel. At first 40–50 drops of cyclohexanol are admitted and the reaction mixture is stirred until the reaction has started (four to five minutes) as is indicated by the evolution of oxides of nitrogen (Note 3). Then the reaction flask is placed in an ice-water bath and cooled until the temperature of the oxidizing mixture is 55–60°. The cyclohexanol is then added as rapidly as possible while the temperature of the mixture is kept within these limits. Toward the end of the oxidation (after about 475 g. of cyclohexanol has been added) the ice bath must be removed and sometimes heat must be applied in order to maintain the temperature and avoid crystallization of adipic acid.
Stirring is continued for about one hour after the addition of the last of the cyclohexanol. Then the mixture is cooled to about 0° and the adipic acid is collected on a suction filter, washed with 500 cc. of ice water, and dried in the air overnight. The yield is 395–410 g. of white crystals which melt at 146–149°. Evaporation of the nitric acid mother liquors yields an additional 30–40 g. of product which melts at 141–144° (Note 4). The total yield of crude adipic acid is 425–440 g. (58–60 per cent of the theoretical amount) (Note 5). This product is pure enough for most purposes. However, a purer product may be obtained by recrystallizing this crude material from 700 cc. of concentrated nitric acid (sp. gr. 1.42). The loss in this purification is about 5 per cent. The recrystallized acid melts at 151–152° (Note 6) and (Note 7).
2. Notes
1.
It is suggested that no catalyst is necessary if the temperature of the reaction mixture, once the reaction has started, is maintained at 85–90°. (W. W. Hartman, private communication.)
2.
The
cyclohexanol used was a commercial grade, which contained practically no
phenol. Over 90 per cent of the product boiled between
158–163°.
3.
It is important that the oxidation start before a large amount of
cyclohexanol has been added or the reaction will become violent. The reaction must be carried out in a good hood.
4.
The
nitric acid mother liquors contain considerable amounts of
adipic acid mixed with
glutaric and
succinic acids. It has not proved practicable to separate these acids by crystallization. However, if the
nitric acid is removed by evaporation and the resulting mixture of acids is esterified with
ethyl alcohol, a mixture of
ethyl succinate (b.p.
121–126°/20 mm.),
ethyl glutarate (b.p.
133–138°/20 mm.), and
ethyl adipate (b.p.
142–147°/20 mm.) can be obtained. These esters can be separated quite satisfactorily by distillation.
5.
The following modified procedure is reported to give better yields. In a
3-l. three-necked flask provided with a stirrer,
reflux condenser, and
dropping funnel set in
asbestos-sodium silicate stoppers, are placed
1900 cc. of 50 per cent nitric acid (
1262 cc. of nitric acid, sp. gr. 1.42, diluted to 1900 cc.) and
1 g. of ammonium vanadate. The flask is surrounded by a
water bath heated to 50–60°, and, while the mixture is stirred,
357 g. (3.5 moles) of commercial cyclohexanol is added very slowly so that the temperature of the bath is maintained at 50–60°. This requires about six to eight hours. The reaction is completed by heating the water bath to boiling until the evolution of
nitrogen oxides has ceased (about one hour). The hot reaction mixture is siphoned off and allowed to cool. The yield of crude
adipic acid is
372 g. (
72 per cent of the theoretical amount). (Duncan G. Foster, private communication.)
The asbestos-sodium silicate stoppers are prepared by cutting thin asbestos paper into strips about 2.5 cm. wide, moistening the strips in water-glass solution, and then winding them around the end of the condenser, for example, until a stopper of the correct size is obtained. After the apparatus is assembled the stoppers are coated with water-glass and allowed to harden overnight.
6.
The
nitric acid mother liquors from the crystallization may be used as part of the acid for a subsequent oxidation.
7.
Adipic acid may also be recrystallized from 2.5 times its weight of water or
50 per cent alcohol. However, these solvents are less satisfactory than
nitric acid.
3. Discussion
Adipic acid can be prepared by the oxidation of
cyclohexanol and
cyclohexanone with
nitric acid1 or
potassium permanganate.
2 The procedure described is adapted from the patent of the Deutsche Hydrierwerke A.-G.
1
Other methods of preparing
adipic acid are the oxidation of
cyclohexene with
dichromate and
sulfuric acid3 and the interaction of
γ-bromobutyric ester with
sodium malonic ester followed by hydrolysis and decarboxylation of the resulting
triethyl 1,4,4-butanetricarboxylate.
4This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
oxides of nitrogen
glutaric
succinic acids
asbestos-sodium silicate
nitrogen oxides
γ-bromobutyric ester
sodium malonic ester
ethyl alcohol,
alcohol (64-17-5)
sulfuric acid (7664-93-9)
Adipic acid (124-04-9)
nitric acid (7697-37-2)
ammonium vanadate (7803-55-6)
Cyclohexanol (108-93-0)
phenol (108-95-2)
ethyl succinate
ethyl glutarate (1070-62-8)
Ethyl adipate (626-86-8)
Cyclohexanone (108-94-1)
potassium permanganate (7722-64-7)
Cyclohexene (110-83-8)
dichromate
triethyl 1,4,4-butanetricarboxylate
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