Methanediol

Methanediol, also known as formaldehyde monohydrate or methylene glycol, is an organic compound with chemical formula CH₂(OH)₂. It is the simplest geminal diol, and formally the second simplest carbohydrate (after formaldehyde).

Methanediol is a product of the hydration of formaldehyde H₂C=O, and predominates in water solution: the equilibrium constant being about 10³, and in a 5% by weight solution of formaldehyde in water, 80% is in the methanediol form.

The compound is of some relevance to astrochemistry.

Methanediol is listed as one of the main ingredients of "Brazilian blowout", a hair-straightening formula marketed in the US. The equilibrium with formaldehyde may cause some concern as formaldehyde in hair straighteners is a health hazard.