Diacids will become more important to the cosmetic industry since they are used to make polyesters, which are of growing importance. Common diacids are shown in Table 1.
Oxalic acid is manufactured by the oxidation of carbohydrates or glucose using nitric acid or air in the presence of vanadium pentoxide. Oxalic acid is a strong acid—approximately 3,000 times stronger than acetic acid. Oxalic acid's main applications include cleaning or bleaching. Most oxalic acid is used as a cleaning agent, especially for the removal of rust.
Malonic acid can be made from chloroacetic acid. It occurs in nature as the calcium salt in beet roots. Malonic acid condenses with urea to form barbituric acid.
Azelaic acid is a saturated dicarboxylic acid found in wheat, rye and barley. It is a natural substance that is produced by Malassezia furfur, also known as Pityrosporum ovale, a yeast that lives on normal skin. Commercially, it is made by the ozonolysis of oleic acid, which results in pelargonic and azelaic acids. Azelic acid acts as: an antibacterial, keratolytic, comedolytic, scavenger of free radicals, an anti-inflammatory agent and a skin lightener; it is non-toxic and well-tolerated by most patients.1 Therefore, it is used to treat mild to moderate acne. Azelaic acid is also used as a topical gel treatment for rosacea due to its ability to reduce inflammation. In some cases, females have reported hair growth on their face and neck, and azelaic acid may be useful as a hair growth stimulant.
Succinic acid is a natural product and a component of the citric acid cycle. It is used as a food additive and dietary supplement, and is approved by the US Food and Drug Administration as safe.
Glutaric acid can be prepared by the ring-opening of butyrolactone. It is a common plasticizer and precursor to polyesters.
Adipic acid is produced from a mixture of cyclohexanol and cyclohexanone. Adipic acid has been incorporated into controlled-release formulation matrix tablets to obtain pH-independent release for both weakly basic and weakly acidic drugs.
Pimelic acid has been synthesized from cyclohexanone and from salicylic acid. Derivatives of pimelic acid are involved in the biosynthesis of lysine.
Sebacic acid is a naturally occurring acid, but it is derived commercially from castor oil, mostly in China. Sebacic acid is used in plasticizers, lubricants and hydraulic fluids. Sebacic acid is also used as an intermediate for aromatics, antiseptics and painting materials.