Hydroxymethyl group
In chemistry, the hydroxymethyl group (also called methylol group) is a functional group with the structural formula –CH 2 –OH. The group consists of a methylene group (–CH 2 -) with a hydroxyl group (–OH), so the respective compounds belong to the alcohols . The hydroxymethyl group has the same empirical formula as the methoxy group (–O – CH 3 ), but differs from it in the location of the oxygen atom, the orientation of the remainder of the molecule and the chemical properties (see isomerism ).
The simplest chemical compounds with a hydroxymethyl group include methanol (H – CH 2 –OH) and ethanol (CH 3 –CH 2 –OH).
The hydroxymethyl group can be introduced into CH-acidic compounds by aldol reaction with formaldehyde . This is used, for example, in the synthesis of pentaerythritol , trimethylolpropane or TRIS or in the industrial production of aminoplasts . Hydroxymethyl groups can be introduced into aromatic compounds by electrophilic substitution with formaldehyde in an acidic medium.
Among other things, derivatives of benzyl alcohol are also of interest in preparation . Under acidic conditions, their hydroxyl groups can be protonated and then split off as water, whereby a well mesomeric-stabilized benzyl cation is formed. In the presence of nucleophilic anions , these will saturate the benzylic position. This is used, for example, in the Blanc reaction . In the presence of hydrochloric acid , the hydroxy function is first split off from a benzyl alcohol. A chloride ion of hydrochloric acid is then deposited on the resulting cation and a derivative of benzyl chloride is formed .
The methylol cation is formed from formaldehyde and the proton of an acid, e.g. B. hydrochloric acid . Methylol cations occur as intermediates in the manufacture of novolaks .
The hydroxymethyl group should not be confused with the hydroxyethyl group.
See also
Individual evidence
- ^ Manfred D. Lechner, Klaus Gehrke, Eckhard Nordmeier: Makromolekulare Chemie. A textbook for chemists, physicists, materials scientists and process engineers. 4th, revised and expanded edition. Birkhäuser, Basel et al. 2010, ISBN 978-3-7643-8890-4 , pp. 130-131.