carboxylaat

Carboxylaat, or carboxylate, is the anion derived from a carboxylic acid by deprotonation. Its general formula is R-COO−, and it commonly forms salts with metals such as sodium, potassium, or ammonium. Examples include acetate (CH3COO−), benzoate (C6H5COO−), and propionate (C2H5COO−). In solution, carboxylates are the conjugate bases of carboxylic acids, and their pKa values are typically around 4–5 for the corresponding acids, making them weak bases.

Carboxylates are stabilized by resonance between the two oxygen atoms, which distributes negative charge over the carboxyl group. They are often found as coordinating ligands in metal complexes, where they can bind in monodentate or bidentate modes and sometimes bridge between metal centres. As salts and in solution, they are generally water-soluble and can act as mild bases and nucleophiles. They also serve as useful leaving groups in acyl substitution reactions and as participants in the formation of mixed anhydrides.

Preparation typically involves neutralization of carboxylic acids with bases (alkali or ammonium bases) or hydrolysis/saponification of esters. Carboxylates occur widely in nature and industry: many are food additives or preservatives (for example, sodium benzoate, sodium citrate, calcium propionate) and intermediates in organic synthesis or coordination chemistry.

Well-known examples include sodium acetate, sodium benzoate, and sodium citrate. Carboxylates play roles in biochemistry, catalysis, and materials science, where their properties as weak bases, nucleophiles, and ligands are exploited.