adipic

Adipic acid, also known as hexanedioic acid, is a colorless, crystalline dicarboxylic acid with the formula HOOC-(CH2)4-COOH. It is a widely used industrial chemical and serves as a key building block in the production of polyamides, polyesters, and plasticizers. In its acidic form, it contributes two carboxyl groups capable of forming amide and ester linkages.

Production and occurrence

Adipic acid is produced predominantly by the oxidation of cyclohexanone and cyclohexanol (KA oil) to adipic acid, typically using nitric acid as the oxidant. The process yields nitrous oxide as a by-product, which has raised environmental concerns. The crude product is purified and can be isolated as adipic acid or converted to salts or derivatives for various downstream applications. It is largely synthetic and not derived from natural reserves in useful quantities.

Applications

The largest use of adipic acid is in the manufacture of nylon-6,6, by condensation with hexamethylenediamine to form the repeating unit of the polymer. It is also converted to adipate esters, such as dioctyl adipate, which function as plasticizers for plastics and coatings. Additional uses include intermediates for polyurethanes, resins, lubricants, and specialty chemicals.

Safety and regulation

Adipic acid is of relatively low acute toxicity but can cause irritation to skin, eyes, and the respiratory tract. It should be handled with appropriate industrial hygiene. In production, attention to emissions control is important due to nitrous oxide formation, and regulatory measures address environmental impact and worker exposure.