To prevent polymerization of formaldehyde, what is added to commercial stock solutions?

• A. Methyl alcohol
• B. Water
• C. Acetic acid
• D. Glycerol

Answer: (A)

Formaldehyde in water is prone to polymerizing and forming solid polymers like paraformaldehyde if it isn’t stabilized during storage. The standard way to prevent this is to add a small amount of an alcohol, with methanol being the classic stabilizer used in commercial stock solutions. Methanol sits in the solution and forms a reversible adduct with some of the formaldehyde, such as methoxymethanol, which lowers the concentration of free aldehyde available to link up into polymer chains. This keeps the solution from polymerizing as it sits on the shelf.

Water by itself won’t stop polymerization; adding acid like acetic acid would alter pH and is not used for stabilization in this context. Glycerol can act as a stabilizer in some formulations, but the established, widely used stabilizer for formaldehyde stock solutions is methanol.