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Adipic acid (IUPAC systematic name: hexanedioic acid) is a dicarboxylic acid. It is a white crystalline powder. Due to its long aliphatic chain, it is not very soluble in water.
Historically, adipic acid was prepared from various fats using oxidation. Current commercial adipic acid is produced from cyclohexane
by two oxidation steps.
- Cyclohexane + O2 → cyclohexanol and cyclohexanone+byproducts
- cyclohexanol/cyclohexanone + nitric acid + air → adipic acid + nitrous oxide
(The mixture of cyclohexanol and cyclohexanone produced from cyclohexane is commercially called "KA oil", the abbreviation of "Ketone-Alcohol oil".)
Other patented processes include those using phenol as feedstock. For example, phenol can be oxidized to KA oil, which is further processed give adipic acid.
Utilizing principles of green chemistry, a new method of synthesis has been developed, which involves oxidizing cyclohexene with hydrogen peroxide via a tungsten catalyst and a phase transfer catalyst to produce adipic acid. The waste product is water.
By far the main use of adipic acid is as monomer for the production of nylon
by a polycondensation
reaction with hexamethylene diamine
. Other uses include:
- Monomer for production of Polyurethane
- reactant to form plasticizers and lubricant components
- Food Ingredient as a flavorant and gelling aid.E-number E355.
- 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