Adipic acid, also known as hexanedioic acid, is a white crystalline organic compound (C6H11O4), is derived from the oxidations of various fats. This organic compound is the most important synthetic dicarboxylic acid produced annually. It has a slight acidic taste and a very faint odor. Also, it is less soluble in water and is soluble in alcohol and acetone. Adipic acid is used as precursor in manufacture of nylon. It is also used in chemical industry to produce other polymers, detergents, plasticizers and coatings. Esters of adipic acid which are known as adipates are used as softeners in plastic and as synthetic grease base oils. Adipic acid causes serious damage to eyes and is mildly toxic so it should be handled carefully. This acid produced mild to no skin irritation, whereas its powdered form may irritate the mucous membranes of the lungs and nose of humans.
Adipic acid is produced through a two-stage process. The first stage of manufacturing usually involves the oxidation of cyclohexane to form cyclohexanone/cyclohexanol mixture. The second stage entails oxidizing this mixture with nitric acid to produce adipic acid. N2O is produced as a byproduct during the nitric acid oxidation stage and is potentially emitted in the waste gas stream during which N2O is generated in the second stage.
Manufacturing of Nylon-6,6
As a monomer, adipic acid is used for the synthesis of polyamide Nylon 6,6. The polycondensation of hexamethylenediamine and adipic acid gives us the product Nylon 6,6. These polyamides are very sensitive to impurities and their coloring capacity and strength depend on the purity of raw material. Nylon 6, 6 is mainly used in textile and plastics industries
As an industrial intermediate, when reacted with other chemicals, adipic acid forms lubricant, solvent and other chemical products such as dimethyl adipate (used as solvent in industrial reactions, and in consumer paint and caulk strippers), and dioctyl adipate (used as plasticizer in PVC films).
Adipic is used for flux activation and its weak acid properties help with metal cleaning. It is even used as a binder in tablet dishwashing detergents and as glass interleaving powders to protect flat glass products from damaging corrosive reactions in humid storage and transport environments
Food & Beverage Industry
Adipic acid is added as main acid in bottled drinks, giving them a bubbly fizz. It adds a tart flavor to fruit juice and gelatin. Found in many powdered food and drink, adipic acid helps to intensify the sweet flavor. It also allows jams and jellies to hold their jiggle shape and acts a leavening agent in baking powder, cake mixes and baked goods. Adipic acid is also frequently added to edible oils, prolonging the time it takes for them to become rancid.
Food grade adipic acid is used to help control delivery of medicines to obtain a pH-independent release for both weakly acidic and weakly basic drugs. Meanwhile, it can also be found in polymer coating of hydrophilic monolithic systems to modulate pH and result in zero-order release of a hydrophilic drug.