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 the simplest sugar alcohol. In aqueous solutions it coexists with oligomers (short polymers). The compound is closely related and convertible to the industrially significant derivatives paraformaldehyde ((CH2O)n), formaldehyde (H2C=O), and 1,3,5-trioxane ((CH2O)3).[3]

Skeletal formula of methanediol with some explicit hydrogens added
Spacefill model of methanediol
Ball and stick model of the methanediol
Preferred IUPAC name
Other names
  • Formaldehyde hydrate
  • Formaldehyde monohydrate
  • Methylene glycol
  • 463-57-0 checkY
3D model (JSmol)
  • Interactive image
Abbreviations MADOL
  • CHEBI:48397 checkY
  • 71348 checkY
ECHA InfoCard 100.006.673 Edit this at Wikidata
EC Number
  • 207-339-5
  • 79015
  • 6Z20YM9257 checkY
  • DTXSID50196801 Edit this at Wikidata
  • InChI=1S/CH4O2/c2-1-3/h2-3H,1H2 checkY
  • OCO
Molar mass 48.041 g·mol−1
Appearance Colourless liquid
Density 1.199 g cm−3[citation needed]
Boiling point 194 °C (381 °F; 467 K) at 101 kPa[citation needed]
Vapor pressure 16.1 Pa[citation needed]
Acidity (pKa) 13.29[2]
1.401[citation needed]
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.

Gaseous methanediols can be generated by electron irradiation and sublimation of a mixture of methanol and oxygen ices.[5]

Methanediol is believed to occur as an intermediate in the decomposition of carbonyl compounds in the atmosphere, and as a product of ozonolysis on these compounds.[5]


Methanediol, rather than formaldehyde, is listed as one of the main ingredients of "Brazilian blowout", a hair-straightening formula marketed in the United States. 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. ^ a b Zhu, Cheng; Kleimeier, N. Fabian; Turner, Andrew M.; Singh, Santosh K.; Fortenberry, Ryan C.; Kaiser, Ralf I. (4 January 2022). "Synthesis of methanediol [CH 2 (OH) 2 ]: The simplest geminal diol". Proceedings of the National Academy of Sciences. 119 (1): e2111938119. Bibcode:2022PNAS..11911938Z. doi:10.1073/pnas.2111938119. PMC 8740743. PMID 34969838.
  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.