Adipic acid

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.

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Preparation

Historically, adipic acid was prepared from various fats using oxidation. Current commercial adipic acid is produced from cyclohexane by two oxidation steps.

1. Cyclohexane + O₂ → cyclohexanol and cyclohexanone
2. 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.^[1]

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.^[2] The waste product is water.

Uses

By far the main use of adipic acid is as monomer for the production of nylon by a polycondensation reaction with hexamethylene diamine forming 6,6-nylon. 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

References

1. ^ U.S. Patent 7,250,537 
2. ^ 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): 1646-7. doi:10.1126/science.281.5383.1646. PMID 9733504.