Carboxy

Carboxy, in chemistry, refers to the carboxyl functional group or substances containing it. The carboxyl group is a carbonyl group (C=O) bonded to a hydroxyl group (OH) on the same carbon, giving the formula -COOH. This group is the defining feature of carboxylic acids and related derivatives.

The carboxyl group is acidic. In water, it can donate a proton to form a carboxylate anion (RCOO−), which is stabilized by resonance between two oxygen atoms. This resonance stabilization accounts for the relatively high acidity of carboxylic acids compared with many other organic acids; typical pKa values are around 4–5 for simple aliphatic carboxylic acids, though stronger or weaker acids occur with different substituents. The presence of the carboxylate also influences solubility: short-chain carboxylic acids are moderately soluble in water, while longer carbon chains increase hydrophobic character.

Carboxyl groups occur widely in biology and industry. They are present in amino acids, fatty acids, and many vitamins, giving amino acids their acidic properties and fatty acids their carboxylate forms in metabolism. In industry, carboxylic acids and their esters are central to the production of polymers (polyesters), solvents, flavors, and pharmaceuticals. They participate in a range of reactions, notably esterification with alcohols to form esters, conversion to acid chlorides for further derivatization, amidation to amides, and decarboxylation under heating or catalytic conditions.

Common examples include formic acid (HCOOH), acetic acid (CH3COOH), and benzoic acid (C6H5COOH). The carboxyl group’s chemistry underpins many functional and structural roles in chemistry and biochemistry.