Karboksülaat

Karboksülaat, in English known as carboxylate, is the anion formed when a carboxylic acid loses a proton. Its general formula is R–COO−, where R denotes an organic group. Carboxylates occur widely as the conjugate bases of carboxylic acids and in the salts formed with metal cations such as sodium or potassium.

The structure of a carboxylate is stabilized by resonance. The negative charge is delocalized over the two oxygens of the carboxylate group, giving two equivalent resonance forms. This delocalization reduces reactivity compared with a localized alkoxide and contributes to the relatively high acidity of carboxylic acids (pKa typically ~4–5) and to the stability of carboxylate salts.

Formation and examples: carboxylates are produced by deprotonation of carboxylic acids with bases (for example NaOH or KOH) and by the base‑catalyzed hydrolysis or saponification of esters. When isolated as salts, common examples include sodium acetate (CH3COONa) and potassium benzoate (C6H5COOK). In organic synthesis, carboxylates can also act as leaving groups in acyl substitution reactions and as ligands for metal centers in coordination chemistry.

Properties and applications: carboxylates are typically polar and water‑soluble, especially for small R groups; solubility decreases with longer hydrophobic chains. They form stable metal complexes and find use in buffering systems (for example, acetate buffer around pH 4.75). Biologically, carboxylate groups are present on amino acids and fatty acids and are usually deprotonated at physiological pH, enabling enzymatic interactions and metal coordination.

See also: carboxylic acids, esters, salts, buffering systems.