Adipic acid

Names
Preferred IUPAC name

Hexanedioic acid

Other names

Adipic acid
Butane-1,4-dicarboxylic acid
Hexane-1,6-dioic acid
1,4-butanedicarboxylic acid

Identifiers

CAS Number

* 124-04-9 Y

3D model (JSmol)

* Interactive image
* Interactive image

Beilstein Reference

| 1209788
ChEBI |

* CHEBI:30832 Y

ChEMBL |

* ChEMBL1157 Y

ChemSpider |

* 191 Y

EC Number |

* 204-673-3

Gmelin Reference

| 3166
KEGG |

* D08839 Y

PubChem CID

* 196

RTECS number |

* AU8400000

UNII |

* 76A0JE0FKJ Y

UN number | 3077

InChI

* InChI=1S/C6H10O4/c7-5(8)3-1-2-4-6(9)10/h1-4H2,(H,7,8)(H,9,10) Y

Key: WNLRTRBMVRJNCN-UHFFFAOYSA-N Y

* InChI=1/C6H10O4/c7-5(8)3-1-2-4-6(9)10/h1-4H2,(H,7,8)(H,9,10)

Key: WNLRTRBMVRJNCN-UHFFFAOYAY

SMILES

* O=C(O)CCCCC(=O)O

* C(CCC(=O)O)CC(=O)O

Properties

Chemical formula

| C6H10O4
Molar mass | 146.142 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)

Solubility in water

| 14 g/L (10 °C)
24 g/L (25 °C)
1600 g/L (100 °C)
Solubility | Very soluble in methanol, ethanol
soluble in acetone, acetic acid
slightly soluble in cyclohexane
negligible in benzene, petroleum ether
log P | 0.08
Vapor pressure | 0.097 hPa (18.5 °C) = 0.073 mmHg
Acidity (pKa)  | 4.43, 5.41
Conjugate base | Adipate
Viscosity | 4.54 cP (160 °C)
Structure

Crystal structure

| Monoclinic
Thermochemistry

Std enthalpy of
formation (ΔfH⦵298)

| −994.3 kJ/mol[3]
Hazards
Safety data sheet | External MSDS
GHS pictograms |
GHS Signal word | Warning

GHS hazard statements

| H319

GHS precautionary statements

| P264, P280, P305+351+338, P337+313
NFPA 704 (fire diamond)  |

Flash point |  196 °C (385 °F; 469 K)

Autoignition
temperature

|  422 °C (792 °F; 695 K)
Lethal dose or concentration (LD, LC):

LD50 (median dose)

| 3600 mg/kg (rat)
Related compounds

Related dicarboxylic acids

| 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).

Infobox references

Tracking categories (test):

* SizeSet

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] but it is known as manufactured E number food additive E355. Salts and esters of adipic acid are known as adipates.

## Contents

* 1 Preparation and reactivity
* 1.1 Alternative methods of production
* 1.2 Reactions
* 2 Uses
* 2.1 In medicine
* 2.2 In foods
* 3 Safety
* 4 Environmental
* 5 Adipate salts and esters
* 6 References
* 7 Appendix
* 8 External links

## Preparation and reactivity

Adipic acid is produced by oxidation of a mixture of cyclohexanone and cyclohexanol, which is called KA oil, an abbreviation of ketone-alcohol oil. Nitric acid is the oxidant. The pathway is multistep. Early in the reaction, the cyclohexanol is converted to the ketone, releasing nitrous acid:

HOCH(CH

5 \+ HNO
3 → O=C(CH

5 \+ HNO
2 \+ H

The cyclohexanone is then nitrosated, setting the stage for the scission of the C-C bond:

HNO
2 \+ HNO
3 → [NO+
]NO
3]−
\+ H

O=C(CH

5 \+ NO+
→ O=C(CHNO)(CH

4 \+ H+

Side products of the method include glutaric and succinic acids. Nitrous oxide is produced in about one to one mole ratio to the adipic acid,[5] as well, via the intermediacy of a nitrolic acid.[4]

Related processes start from cyclohexanol, which is obtained from the hydrogenation of phenol.[4][6]

### 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.[7] The waste product is water.

Historically, adipic acid was prepared by oxidation of various fats,[8] 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.[9]

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.[10]

## Uses

About 60% of the 2.5 billion kg of adipic acid produced annually is used as monomer for the production of nylon[11] 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.[12]

### 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.[13]

### In foods

Small but significant amounts of adipic acid are used as a food ingredient as a flavorant and gelling aid.[14] 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.[2] Adipic acid, rare in nature, does occur naturally in beets, but this is not an economical source for commerce compared to industrial synthesis.[15]

## Safety

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

## Environmental

The production of adipic acid is linked to emissions of N2O,[16] 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:[17]

2 N2O → 2 N2 \+ O2

## Adipate salts and esters

Structural formula of the adipate dianion

The anionic (HO2C(CH2)4CO2−) and dianionic (−O2C(CH2)4CO2−) forms of adipic acid are referred to as adipates. An adipate compound is a carboxylate salt or ester of the acid.

Some adipate salts are used as acidity regulators, including:

* Sodium adipate (E number E356)
* Potassium adipate (E357)

Some adipate esters are used as plasticizers, including:

* Bis(2-ethylhexyl) adipate
* Dioctyl adipate
* Dimethyl adipate

## References

1. ↑ Mac Gillavry, C. H. (2010). "The crystal structure of adipic acid". Recueil des Travaux Chimiques des Pays-Bas 60 (8): 605–617. doi:10.1002/recl.19410600805.
2. ↑ 2.0 2.1 Template:Cite Merck Index
3. ↑ Template:CRC94
4. ↑ 4.0 4.1 4.2 4.3 4.4 Musser, M. T. (2005). "Adipic Acid". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a01_269. ISBN 3527306730.
5. ↑ Parmon, V. N.; Panov, G. I.; Uriarte, A.; Noskov, A. S. (2005). "Nitrous oxide in oxidation chemistry and catalysis application and production". Catalysis Today 100 (2005): 115–131. doi:10.1016/j.cattod.2004.12.012.
6. ↑ Ellis, B. A. (1925). "Adipic Acid". Organic Syntheses 5: 9. http://www.orgsyn.org/demo.aspx?prep=CV1P0018. ;  Collective Volume, 1, pp. 560
7. ↑ 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. doi:10.1126/science.281.5383.1646. PMID 9733504. Bibcode: 1998Sci...281.1646S.
8. ↑ Ince, Walter (1895). "Preparation of adipic acid and some of its derivatives". Journal of the Chemical Society, Transactions 67: 155–159. doi:10.1039/CT8956700155. https://books.google.com/books?id=BgE3AAAAYAAJ&pg=PA155.
9. ↑ Cornils, Boy; Lappe, Peter (2000). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a08_523.
10. ↑ Thorpe, J. F.; Kon, G. A. R. (1925). "Cyclopentanone". Organic Syntheses 5: 37. http://www.orgsyn.org/demo.aspx?prep=CV1P0192. ;  Collective Volume, 1, pp. 192
11. ↑ "Adipic Acid". http://pcinylon.com/index.php/markets-covered/adipic-acid. PCI abstract for adipic acid
12. ↑ "Polyvinylchloride - an overview | ScienceDirect Topics". https://www.sciencedirect.com/topics/nursing-and-health-professions/polyvinylchloride.
13. ↑ Roew, Raymond (2009), "Adipic Acid", Handbook of Pharmaceutical Excipients, pp. 11–12
14. ↑ "Cherry Jell-O Nutrition Facts". Kraft Foods. http://www.kraftbrands.com/Jello/nutritioninfo.aspx?Site=1&Product=4300020003.
15. ↑ American Chemical Society (9 February 2015). "Molecule of the Week: Adipic Acid". https://www.acs.org/content/acs/en/molecule-of-the-week/archive/a/adipic-acid.html.
16. ↑ US EPA (12 August 2013). "U.S. Greenhouse Gas Inventory Report, Chapter 4. Industrial Processes". http://www.epa.gov/climatechange/Downloads/ghgemissions/US-GHG-Inventory-2013-Chapter-4-Industrial-Processes.pdf.
17. ↑ 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.

## Appendix

* 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

## External links

* International Chemical Safety Card 0369
* SIDS Initial Assessment Report for Adipic acid from the Organisation for Economic Co-operation and Development (OECD)
* adipic acid on chemicalland

* v
* t
* e

Linear saturated dicarboxylic acids (H2OC-R-CO2H)

* Ethanedioic acid (Oxalic acid) C2H2O4
* Propanedioic acid (Malonic acid) C3H4O4
* Butandioic acid (Succinic acid) C4H6O4
* Pentanedioic acid (Glutaric acid) C5H8O4
* Hexanedioic acid (Adipic acid) C6H10O4
* Heptanedioic acid (Pimelic acid) C7H12O4
* Octanedioic acid (Suberic acid) C8H14O4
* Nonanedioic acid (Azelaic acid) C9H16O4
* Decanedioic acid (Sebacic acid) C10H18O4

Category:Dicarboxylic acids

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*[CID]: Compound ID
*[H319]: Causes serious eye irritation
*[P264]: Wash … thoroughly after handling
*[P280]: Wear protective gloves/protective clothing/eye protection/face protection
*[P305+351+338]: IF IN EYES: Rinse continuously with water for several minutes. Remove contact lenses if present and easy to do – continue rinsing
*[P337+313]: Get medical advice/attention
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