What Are Dicarboxylic Acids? Sources and Uses
Explore dicarboxylic acids, organic compounds whose structure makes them vital building blocks in everything from biological systems to industrial polymers.
Dicarboxylic acids are organic compounds defined by the presence of two carboxyl functional groups. These molecules are found in natural biological processes and are also synthesized for industrial applications. Their dual role in both nature and manufacturing makes them a useful class of chemicals.
Defining Dicarboxylic Acids
A dicarboxylic acid’s structure is defined by two carboxylic acid (-COOH) groups, reflected in the general formula HOOC-(CH2)n-COOH. The variable ‘n’ represents the carbon chain linking the two acidic ends. The length of this central chain is a primary determinant of the acid’s specific properties.
The two carboxyl groups influence the physical characteristics of these compounds. Dicarboxylic acids are typically colorless, crystalline solids at room temperature with higher melting points and greater water solubility than monocarboxylic acids of similar molecular weight. This is because the two carboxyl groups allow for more extensive hydrogen bonding.
These acids are dibasic, meaning they can donate two protons (hydrogen ions). The first proton is released more readily than the second. After the first group ionizes, the molecule’s negative charge makes it more difficult to remove the second proton. This two-stage ionization is a distinct feature of their chemical identity.
Sources of Dicarboxylic Acids
Dicarboxylic acids originate from both natural and synthetic pathways. In nature, they are components of metabolic processes, such as succinic acid in the citric acid cycle (Krebs cycle) that generates cellular energy for most living organisms. Another example is oxalic acid, which is found in plants like spinach and rhubarb.
Industrially, specific dicarboxylic acids are manufactured in large quantities. Adipic acid, for example, is an industrial chemical not commonly found in nature. Its production starts with petroleum-based feedstocks like cyclohexane, which is converted into adipic acid through a multi-step oxidation process, often involving nitric acid.
Other methods involve biotechnology, where microorganisms produce dicarboxylic acids from renewable resources. For example, yeasts from the genus Candida can convert fatty acids from vegetable oils into long-chain dicarboxylic acids via ω-oxidation. This route represents a more sustainable approach to synthesis.
Commercial and Biological Uses
The applications of dicarboxylic acids are widespread. One of their primary roles is in the polymer industry as monomers—small molecules joined together to form long chains. Adipic acid is a main ingredient in the synthesis of Nylon 6,6, a durable and versatile polyamide fabric used in textiles, carpets, and automotive parts. In this process, adipic acid is reacted with hexamethylenediamine to create the polymer chains that give nylon its properties.
Dicarboxylic acids also have uses in skincare and pharmaceuticals. Azelaic acid is used topically to treat skin conditions like acne and rosacea by reducing inflammation, clearing pores, and providing antibacterial action. Available in gel or cream form, it helps manage the redness and bumps from these conditions.
The utility of these acids extends to other areas. They are used as food additives to function as acidity regulators and flavoring agents. Certain dicarboxylic acid esters are used as plasticizers to increase the flexibility of PVC plastics, while others are components in the formulation of lubricants and adhesives.