Adipic acid

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Adipic acid
Adipic acid
Adipic-acid-3D-balls.png
Identifiers
CAS number 124-04-9 YesY
PubChem 196
ChemSpider 191 YesY
UNII 76A0JE0FKJ YesY
EC-number 204-673-3
KEGG D08839 YesY
ChEBI CHEBI:30832 YesY
ChEMBL CHEMBL1157 YesY
RTECS number AU8400000
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C6H10O4
Molar mass 146.14 g mol−1
Appearance White crystals [1]
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 1.4 g/100 mL (10 °C)
2.4 g/100 mL (25 °C)
160 g/100 mL (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
Crystal structure monoclinic
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-1021 KJ/mol
Hazards
MSDS External MSDS
EU Index 607-144-00-9
EU classification Irritant (Xi)
R-phrases 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
Flash point 196 °C (385 °F; 469 K)
LD50 3600 mg/kg (rat)
Related compounds
Related dicarboxylic acids glutaric acid
pimelic acid
Related compounds hexanoic acid
adipic acid dihydrazide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Adipic 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.[2]

Preparation and reactivity[edit]

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 → OC6H10 + 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.[2]

Related processes start from cyclohexanol, which is obtained from the hydrogenation of phenol.[2][3]

Alternative methods of production[edit]

Several methods have been developed by carbonylation of butadiene. For example, the hydrocarboxylation proceeds as follows:[2]

CH2=CHCH=CH2 + 2 CO + 2 H2O → HO2C(CH2)4CO2H
See also: Heteropoly acid

A method that utilizes principles of green chemistry in that water is the only by-product. Cyclohexene is oxidized with hydrogen peroxide using a tungstate-based catalyst and a phase transfer catalyst.[4] The waste product is water.

Historically, adipic acid was prepared by oxidation of various fats,[5] thus the name (ultimately from Latin adeps, adipis : 'animal fat'; cf. adipose tissue).

Reactions[edit]

Adipic acid is a dibasic acid (can be deprotonated twice). Its pKa's are 4.41 and 5.41.[6]

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.[7]

Uses[edit]

The great majority 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 6,6-nylon. Other major applications also involve polymers: it is a monomer for production of Polyurethane and its esters are plasticizers, especially in PVC.

In medicine[edit]

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.[8]

In foods[edit]

Small but significant amounts of adipic acid are used as a food ingredient as a flavorant and gelling aid.[9] It is used in some calcium carbonate antacids to make them tart.

Safety[edit]

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.[2]

Environmental[edit]

The production of adipic acid is linked to emissions of N
2
O
,[10] a potent greenhouse gas and cause of stratospheric ozone depletion.

References[edit]

  1. ^ http://onlinelibrary.wiley.com/doi/10.1002/recl.19410600805/abstract
  2. ^ a b c d e Musser, M. T. (2005), "Adipic Acid", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a01_269 .
  3. ^ B. A. Ellis (1925), Adipic Acid, Org. Synth. 5: 9 ; Coll. Vol. 1: 560 .
  4. ^ 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 .
  5. ^ Ince, Walter (1895). "Preparation of adipic acid and some of its derivatives". Journal Chemical Society, London 67. doi:10.1039/CT8956700155. Retrieved 27 September 2012. 
  6. ^ Boy Cornils, Peter Lappe "Dicarboxylic Acids, Aliphatic" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_523
  7. ^ J. F. Thorpe and G. A. R. Kon (1925), Cyclopentanone, Org. Synth. 5: 37 ; Coll. Vol. 1: 192 .
  8. ^ Roew, Raymond (2009), "Adipic Acid", Handbook of Pharmaceutical Excipients, pp. 11–12 
  9. ^ "Cherry Jell-O Nutrition Facts". Kraft Foods. Retrieved 21 Mar 2012. 
  10. ^ US EPA. "U.S. Greenhouse Gas Inventory Report, Chapter 4. Industrial Processes". Retrieved 2013-11-29. 

Appendix[edit]

  • E-number E355.
  • 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[edit]