Methylolgruppen

The methylolgruppe, or hydroxymethyl group, is the functional group –CH2OH that can be attached as a substituent to an organic molecule. It is commonly formed by the hydroxymethylation of a substrate with formaldehyde, yielding a CH2OH unit linked to the original framework. In English, the term hydroxymethyl group is often used, while Methylolgruppe is a traditional German designation.

Formation and reactivity arise when formaldehyde acts as an electrophile and adds to nucleophilic sites such as phenolic rings, amines, alcohols, or enolizable carbons. This reaction, often called methylolation, produces R–CH2OH derivatives (hydroxymethyl compounds). The hydroxymethyl group is relatively reactive due to the free alcohol function and can participate in further condensation reactions, including dehydration to form ether or methylene linkages.

In polymer and materials chemistry, hydroxymethyl derivatives are central intermediates in the synthesis of aldehyde-phenol and aldehyde-urea or aldehyde-melamine resins. Through subsequent crosslinking, hydroxymethyl groups form methylene bridges (–CH2–) or methylene ether bridges (–CH2–O–CH2–), creating thermosetting networks. This chemistry underpins phenol-formaldehyde (novolac and resole), urea-formaldehyde, and melamine-formaldehyde resins, which are used in wood adhesives, coatings, laminates, and related products.

Safety and handling revolve around formaldehyde exposure, as formaldehyde and some hydroxymethyl derivatives can be irritants and pose health risks. Proper containment, ventilation, and adherence to regulatory guidelines are standard considerations in work with these species.