methylol

Methylol is a hydroxymethyl substituent, represented as -CH2OH. It is formed when formaldehyde adds to substrates containing an active hydrogen, such as phenols, amines, or alcohols. In this context, methylol describes a reactive moiety rather than a standalone compound, and it is often referred to as a hydroxymethyl group.

In resin chemistry, methylol groups are key intermediates in systems such as phenol-formaldehyde, urea-formaldehyde, and melamine-formaldehyde resins. Formaldehyde reacts with phenol to give methylol phenols, which can reside on the phenolic ring at ortho and para positions. These methylol intermediates serve as precursors for further crosslinking during resin curing.

Reactivity and crosslinking typically occur through condensation reactions. Methylol groups can condense with other methylol groups, releasing water, to form methylene bridges (–CH2–) between aromatic rings or other components. Condensation can also yield ether linkages, depending on the reacting partners and conditions. Through these condensations, a thermosetting network forms, contributing to the hardness and thermal resistance of the final resin.

Nomenclature-wise, methylol is sometimes called a hydroxymethyl group. In practical use, compounds described as methylol derivatives—such as methylol ureas, methylol phenols, or methylol melamines—refer to structures bearing one or more -CH2OH substituents derived from formaldehyde.

Safety and handling considerations arise from the involvement of formaldehyde in forming methylol groups. Formaldehyde is toxic and a regulatory concern in many settings, so processes employing methylol chemistry require appropriate ventilation and controls to manage emissions and exposure.