carboxymethyl

Carboxymethyl is a functional substituent group used in organic and polymer chemistry. It consists of a methylene bridge (-CH2-) attached to a terminal carboxyl group (-COOH), giving the moiety -CH2-COOH when it is bound to a parent molecule. In many contexts the carboxyl group can be deprotonated to form -CH2-COO−, and in salts this unit commonly appears as -CH2-COONa or related cations.

Carboxymethyl groups are typically introduced through carboxymethylation, often using monochloroacetic acid (or its salts) under basic conditions to graft the group onto hydroxyl or amine sites of polymers and biomolecules. This modification can occur on cellulose, starch, chitosan, and other polysaccharides, as well as on proteins and small molecules, producing water-soluble or more highly substitutable derivatives.

The most widespread example is carboxymethyl cellulose (CMC), a water-soluble, anionic polymer used as a thickener, stabilizer, and binder in foods, cosmetics, pharmaceuticals, and paper products. Carboxymethyl substitution increases hydrophilicity, introduces a negative charge, and enhances dispersibility and salt tolerance. Variants include carboxymethyl starch and other carboxymethylated biopolymers, which find roles in food processing, packaging, and drug delivery.

In biochemistry and materials science, carboxymethyl groups are also encountered in conjugation and modification strategies, including the preparation of carboxymethylated derivatives of amino acids and peptides or proteins for research and industrial applications.