Hydroxytricarboxylic

Hydroxytricarboxylic acids are organic compounds characterized by having three carboxyl groups and at least one hydroxyl group within a single molecule. The best-known member is citric acid, or 2-hydroxypropane-1,2,3-tricarboxylic acid, which features three carboxyl groups and a single hydroxyl group attached to the central carbon.

Citric acid occurs naturally in many fruits, most notably citrus fruits, and serves as a central metabolite in cellular energy production. In biochemistry it is a primary intermediate of the tricarboxylic acid (Krebs) cycle, formed from acetyl-CoA and oxaloacetate and subsequently converted to other cycle intermediates. Other hydroxytricarboxylic acids exist, but they are less common in nature and may be produced synthetically or observed as intermediates in specialized metabolic pathways.

The properties of hydroxytricarboxylic acids derive from their multiple acidic groups, giving them high acidity and water solubility. Citric acid, for example, has three acidic protons with pKa values around 3.1, 4.8, and 6.4, and forms citrate anions in solution. These compounds are widely used as food additives and acidulants, chelating agents for metal ions, and components in cosmetics and cleaning products. Industrial production is typically based on microbial fermentation of sugars to yield citric acid, followed by purification.