Adipic acid

Adipic acid
Skeletal formula of adipic acid
Ball-and-stick model of the adipic acid molecule
Names
Preferred IUPAC name
Hexanedioic acid
Other names
Adipic acid
Hexane-1,6-dicarboxylic acid
Hexane-1,6-dioic acid
1,4-butanedicarboxylic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.004.250
EC Number 204-673-3
E number E355 (antioxidants, ...)
KEGG
RTECS number AU8400000
UNII
Properties
C6H10O4
Molar mass 146.14 g·mol−1
Appearance White crystals[1]
Monoclinic prisms[2]
Odor Odorless
Density 1.360 g/cm3
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
log P 0.08
Vapor pressure 0.0728 Pa (18.5 °C)
Acidity (pKa) 4.43, 5.41
Viscosity 4.54 cP (160 °C)
Structure
Monoclinic
Thermochemistry
−994.3 kJ/mol[3]
Hazards
Safety data sheet External MSDS
Irritant (Xi)
R-phrases (outdated) R36
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
1
2
0
Flash point 196 °C (385 °F; 469 K)
422 °C (792 °F; 695 K)
Lethal dose or concentration (LD, LC):
3600 mg/kg (rat)
Related compounds
glutaric acid
pimelic acid
Related compounds
 hexanoic acid
adipic acid dihydrazide
hexanedioyl dichloride
hexanedinitrile
hexanediamide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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.[4]

Preparation and reactivity

Adipic acid is produced from a mixture of cyclohexanol and cyclohexanone 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+

Side products of the method include glutaric and succinic acids. Nitrous oxide is produced as well, via the intermediacy of a nitrolic acid.[4]

Related processes start from cyclohexanol, which is obtained from the hydrogenation of phenol.[4][5]

Alternative methods of production

Several methods have been developed by carbonylation of butadiene. For example, the hydrocarboxylation proceeds as follows:[4]

CH2=CH−CH=CH2 + 2 CO + 2 H2O → HO2C(CH2)4CO2H

Another method is oxidative cleavage of cyclohexene using hydrogen peroxide.[6] The waste product is water.

Historically, adipic acid was prepared by oxidation of various fats,[7] thus the name (ultimately from Latin adeps, adipis – "animal fat"; cf. adipose tissue).

Reactions

Adipic acid is a dibasic acid (it has two acidic groups). The pKa values for their successive deprotonations are 4.41 and 5.41.[8]

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.[9]

Uses

About 60% of the 2.5 billion kg of adipic acid produced annually is used as monomer for the production of nylon [10] 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.

In medicine

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.[11] Adipic acid is used to make bisobrin an antifibrinolytic.

In foods

Small but significant amounts of adipic acid are used as a food ingredient as a flavorant and gelling aid.[12] It is used in some calcium carbonate antacids to make them tart. As an acidulant in baking powders, it avoids the undesireable hygroscopic properties of tartaric acid.[13] Adipic acid, rare in nature, does occur naturally in beets, but this is not an economical source for commerce compared to industrial synthesis.[14]

Safety

Adipic acid, like most carboxylic acids, is a mild skin irritant. It is mildly toxic, with an LD50 of 3600 mg/kg for oral ingestion by rats.[4]

Environmental

The production of adipic acid is linked to emissions of N
2O,[15] 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:[16]

2 N2O → 2 N2 + O2

References

  1. ↑ 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.
  2. ↑ "Adipic Acid". The Merck Index. Royal Society of Chemistry. 2013. Retrieved 2 March 2017. (Subscription required (help)).
  3. ↑ Haynes, W. M., ed. (2013). CRC Handbook of Chemistry and Physics (94th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4665-7114-3.
  4. 1 2 3 4 5 Musser, M. T. (2005). "Adipic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_269.
  5. ↑ Ellis, B. A. (1925). "Adipic Acid". Org. Synth. 5: 9.; Coll. Vol., 1, p. 560
  6. ↑ 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.
  7. ↑ Ince, Walter (1895). "Preparation of adipic acid and some of its derivatives". Journal Chemical Society, London. 67: 155. doi:10.1039/CT8956700155.
  8. ↑ 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
  9. ↑ Thorpe, J. F.; Kon, G. A. R. (1925). "Cyclopentanone". Org. Synth. 5: 37.; Coll. Vol., 1, p. 192
  10. ↑ http://pcinylon.com/index.php/markets-covered/adipic-acid PCI abstract for adipic acid
  11. ↑ Roew, Raymond (2009), "Adipic Acid", Handbook of Pharmaceutical Excipients, pp. 11–12
  12. ↑ "Cherry Jell-O Nutrition Facts". Kraft Foods. Retrieved 21 Mar 2012.
  13. ↑ "Adipic Acid". The Merck Index. Royal Society of Chemistry. 2013. Retrieved 2 March 2017. (Subscription required (help)).
  14. ↑ American Chemical Society (9 February 2015). "Molecule of the Week: Adipic Acid".
  15. ↑ US EPA. "U.S. Greenhouse Gas Inventory Report, Chapter 4. Industrial Processes" (PDF). Retrieved 2013-11-29.
  16. ↑ 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. ISBN 978-94-015-9343-4. doi:10.1007/978-94-015-9343-4_56.

Appendix


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