Adipic acid or hexanedioic acid is the organic compound with the formula (CH2)4(COOH)2. From an industrial perspective, it is the most important dicarboxylic acid: about 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon. Adipic acid otherwise rarely occurs in nature, but it is known as manufactured E number food additive E355.
|Preferred IUPAC name
3D model (JSmol)
|E number||E355 (antioxidants, ...)|
CompTox Dashboard (EPA)
|Molar mass||146.142 g·mol−1|
|Melting point||152.1 °C (305.8 °F; 425.2 K)|
|Boiling point||337.5 °C (639.5 °F; 610.6 K)|
|14 g/L (10 °C) |
24 g/L (25 °C)
1600 g/L (100 °C)
|Solubility||Very soluble in methanol, ethanol |
soluble in acetone
slightly soluble in cyclohexane
negligible in benzene, petroleum ether
insoluble in acetic acid
|Vapor pressure||0.097 hPa (18.5 °C) = 0.073 mmHg|
|Acidity (pKa)||4.43, 5.41|
|Viscosity||4.54 cP (160 °C)|
Std enthalpy of
|Safety data sheet||External MSDS|
|Flash point||196 °C (385 °F; 469 K)|
|422 °C (792 °F; 695 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|3600 mg/kg (rat)|
Related dicarboxylic acids
adipic acid dihydrazide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Preparation and reactivityEdit
Adipic acid is produced from a mixture of cyclohexanone and cyclohexanol called "KA oil", the abbreviation of ketone-alcohol oil. The KA oil is oxidized with nitric acid to give adipic acid, via a multistep pathway. Early in the reaction, the cyclohexanol is converted to the ketone, releasing nitrous acid:
- HOC6H11 + HNO3 → OC(CH2)5 + HNO2 + H2O
Among its many reactions, the cyclohexanone is nitrosated, setting the stage for the scission of the C-C bond:
- HNO2 + HNO3 → NO+NO3− + H2O
- OC6H10 + NO+ → OC6H9-2-NO + H+
Alternative methods of productionEdit
- CH2=CH−CH=CH2 + 2 CO + 2 H2O → HO2C(CH2)4CO2H
With the carboxylate groups separated by four methylene groups, adipic acid is suited for intramolecular condensation reactions. Upon treatment with barium hydroxide at elevated temperatures, it undergoes ketonization to give cyclopentanone.
About 60% of the 2.5 billion kg of adipic acid produced annually is used as monomer for the production of nylon  by a polycondensation reaction with hexamethylene diamine forming nylon 66. Other major applications also involve polymers; it is a monomer for production of polyurethane and its esters are plasticizers, especially in PVC.
Adipic acid has been incorporated into controlled-release formulation matrix tablets to obtain pH-independent release for both weakly basic and weakly acidic drugs. It has also been incorporated into the polymeric coating of hydrophilic monolithic systems to modulate the intragel pH, resulting in zero-order release of a hydrophilic drug. The disintegration at intestinal pH of the enteric polymer shellac has been reported to improve when adipic acid was used as a pore-forming agent without affecting release in the acidic media. Other controlled-release formulations have included adipic acid with the intention of obtaining a late-burst release profile.
Small but significant amounts of adipic acid are used as a food ingredient as a flavorant and gelling aid. It is used in some calcium carbonate antacids to make them tart. As an acidulant in baking powders, it avoids the undesirable hygroscopic properties of tartaric acid. Adipic acid, rare in nature, does occur naturally in beets, but this is not an economical source for commerce compared to industrial synthesis.
The production of adipic acid is linked to emissions of N
2O, a potent greenhouse gas and cause of stratospheric ozone depletion. At adipic acid producers DuPont and Rhodia (now Invista and Solvay, respectively), processes have been implemented to catalytically convert the nitrous oxide to innocuous products:
- 2 N2O → 2 N2 + O2
- Mac Gillavry, C. H. (2010). "The crystal structure of adipic acid". Recueil des Travaux Chimiques des Pays-Bas. 60 (8): 605. doi:10.1002/recl.19410600805.
- "Adipic Acid". The Merck Index. Royal Society of Chemistry. 2013. Retrieved 2 March 2017.
- Haynes, W. M., ed. (2013). CRC Handbook of Chemistry and Physics (94th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4665-7114-3.
- Musser, M. T. (2005). "Adipic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_269.
- Parmon, V. N.; Panov, G. I.; Uriarte, A.; Noskov, A. S. "Nitrous oxide in oxidation chemistry and catalysis application and production". Catalysis Today. 100 (2005): 115–131. doi:10.1016/j.cattod.2004.12.012.
- Ellis, B. A. (1925). "Adipic Acid". Organic Syntheses. 5: 9.; Collective Volume, 1, p. 560
- Sato, K.; Aoki, M.; Noyori, R. (1998). "A "Green" route to adipic acid: direct oxidation of cyclohexenes with 30 percent hydrogen peroxide". Science. 281 (5383): 1646–47. Bibcode:1998Sci...281.1646S. doi:10.1126/science.281.5383.1646.
- Ince, Walter (1895). "Preparation of adipic acid and some of its derivatives". Journal Chemical Society, London. 67: 155. doi:10.1039/CT8956700155.
- Cornils, Boy and Lappe, Peter (2006) "Dicarboxylic Acids, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_523
- Thorpe, J. F.; Kon, G. A. R. (1925). "Cyclopentanone". Organic Syntheses. 5: 37.; Collective Volume, 1, p. 192
- "Archived copy". Archived from the original on 2015-05-18. Retrieved 2015-05-09.CS1 maint: archived copy as title (link) PCI abstract for adipic acid
- Roew, Raymond (2009), "Adipic Acid", Handbook of Pharmaceutical Excipients, pp. 11–12
- "Cherry Jell-O Nutrition Facts". Kraft Foods. Retrieved 21 Mar 2012.
- American Chemical Society (9 February 2015). "Molecule of the Week: Adipic Acid".
- US EPA. "U.S. Greenhouse Gas Inventory Report, Chapter 4. Industrial Processes" (PDF). Retrieved 2013-11-29.
- Reimer, R. A.; Slaten, C. S.; Seapan, M.; Koch, T. A.; Triner, V. G. (2000). "Adipic Acid Industry — N2O Abatement". Non-CO2 Greenhouse Gases: Scientific Understanding, Control and Implementation. Netherlands: Springer. pp. 347–358. doi:10.1007/978-94-015-9343-4_56. ISBN 978-94-015-9343-4.
- U.S. FDA citations – GRAS (21 CFR 184.1009), Indirect additive (21 CFR 175.300, 21 CFR 175.320, 21 CFR 176.170, 21 CFR 176.180, 21 CFR 177.1200, 21 CFR 177.1390, 21 CFR 177.1500, 21 CFR 177.1630, 21 CFR 177.1680, 21 CFR 177.2420, 21 CFR 177.2600)
- European Union Citations – Decision 1999/217/EC – Flavoing Substance; Directive 95/2/EC, Annex IV – Permitted Food Additive; 2002/72/EC, Annex A – Authorized monomer for Food Contact Plastics