The chemical molecule with the formula (CH2)4(COOH)2 is known as adipic acid or hexanedioic acid. It is the most significant dicarboxylic acid from an industrial standpoint; every year, around 2.5 billion kilos of this white crystalline powder are manufactured, mostly as a precursor to the manufacture of nylon. Adipic acid is a synthetic food additive with the E355 designation. It is an uncommon occurrence in nature. Adipates are the name for adipic acid salts and esters.

KA oil, also known as ketone-alcohol oil, is a combination of cyclohexanone and cyclohexanol that is used to make adipic acid. Through a multistep process, KA oil is oxidized with nitric acid to produce adipic acid.

Adipic acid has two acidic groups and is a dibasic acid. Their subsequent deprotonations had pKa values of 4.41 and 5.41.

Adipic acid is suitable for intramolecular condensation processes because it has four methylene groups separating the carboxylate groups. It passes through a process called ketonization when exposed to barium hydroxide at high temperatures, producing cyclopentanone.

Over 60% of the 2.5 billion kg of adipic acid produced annually is used as the monomer when hexamethylene diamine and adipic acid are mixed in a polycondensation process to manufacture nylon 66. The synthesis of polyurethane requires the use of polymers as a monomer, and their esters are utilized as plasticizers, especially in PVC, in other key uses.

To provide pH-independent release for both weakly basic and weakly acidic medicines, adipic acid has been added to controlled-release formulation matrix tablets. Additionally, it has been used to adjust the intragel pH in hydrophilic monolithic systems' polymeric coatings, causing a hydrophilic medication to release in zero orders. When adipic acid was utilized as a pore-forming agent, it was reported that the enteric polymer shellac's disintegration at gut pH improved without influencing its release in the acidic medium.

Adipic acid has also been used in other controlled-release formulations to provide a late-burst release profile.

Adipic acid is a food additive that is utilized in small but considerable concentrations as a flavoring agent and gelling aid. Some calcium carbonate antacids employ it to add tartness. It eliminates tartaric acid's unpleasant hygroscopic qualities when used as an acidulant in baking powders. Even though adipic acid is uncommon in nature, it does exist naturally in beets. However, this is not as cost-effective as industrial production for commercial use.

Like other carboxylic acids, adipic acid causes very minor skin irritation. With a median lethal dosage of 3600 mg/kg for oral intake by rats, it is a slightly poisonous substance.

Adipic acid synthesis is associated with N2O emissions, a strong greenhouse gas that contributes to the destruction of stratospheric ozone. Processes have been put in place at the adipic acid manufacturers DuPont and Rhodia (now Invista and Solvay, respectively) to catalytically transform nitrous oxide into harmless products:2 N2O = 2 N2 + O2(adipate salts and esters)