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. It is not encountered in pure form, but as aqueous solutions, where it coexists with oligomers (short polymers). The compound is well characterized but of less technological significance than related paraformaldehyde ((CH2O)n), formaldehyde (H2C=O), and trioxane ((CH2O)3).[3]

Skeletal formula of methanediol with some explicit hydrogens added
Spacefill model of methanediol
Ball and stick model of the methanediol
IUPAC name
Other names
  • Formaldehyde hydrate
  • Formaldehyde monohydrate
  • Methylene glycol
3D model (JSmol)
Abbreviations MADOL
ECHA InfoCard 100.006.673
EC Number
  • 207-339-5
Molar mass 48.041 g·mol−1
Appearance Colourless liquid
Density 1.199 g cm−3
Boiling point 194 °C (381 °F; 467 K) at 101 kPa
Vapor pressure 16.1 Pa
Acidity (pKa) 13.29[2]
Flash point 99.753 °C (211.555 °F; 372.903 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Methanediol is a product of the hydration of formaldehyde. The equilibrium constant for hydration is estimated to be 103,[4] CH2(OH)2 predominates in dilute (<0.1%) solution. In more concentrated solutions, it oligomerizes to HO(CH2O)nH.[3]


The dianion, methanediolate, is believed to be an intermediate in the crossed Cannizzaro reaction.

The compound is of some relevance to astrochemistry.[5]


Methanediol, rather than formaldehyde, is listed as one of the main ingredients of "Brazilian blowout", a hair-straightening formula marketed in the US. The equilibrium with formaldehyde has caused concern since formaldehyde in hair straighteners is a health hazard,[6][7] but the risk has been disputed.[8]

See alsoEdit


  1. ^ "Methanediol - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification and Related Records. Retrieved 20 October 2011.
  2. ^ Bell, R. P.; McTigue, P. T. (1960). "603. Kinetics of the aldol condensation of acetaldehyde". Journal of the Chemical Society (Resumed): 2983. doi:10.1039/JR9600002983.
  3. ^ a b Reuss, Günther; Disteldorf, Walter; Gamer, Armin Otto; Hilt, Albrecht (2000). "Formaldehyde". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_619.
  4. ^ Eric V. Anslyn, Dennis A. Dougherty (2006), Modern physical organic chemistry. University Science Books. ISBN 1-891389-31-9. 1095 pages
  5. ^ Garrod, Robin T.; Weaver, Susanna L. Widicus; Herbst, Eric (2008). "Complex Chemistry in Star‐forming Regions: An Expanded Gas‐Grain Warm‐up Chemical Model". The Astrophysical Journal. 682 (1): 283–302. arXiv:0803.1214. Bibcode:2008ApJ...682..283G. doi:10.1086/588035.
  6. ^ "Hair Smoothing Products That Could Release Formaldehyde". Occupational Safety and Health Administration.
  7. ^ SpecialChem. "Industry News".
  8. ^ Golden, R.; Valentini, M. (July 2014). "Formaldehyde and methylene glycol equivalence: Critical assessment of chemical and toxicological aspects". Regulatory Toxicology and Pharmacology. 69 (2): 178–186. doi:10.1016/j.yrtph.2014.03.007. PMID 24709515.