Methyloxonium

Methyloxonium
Identifiers
3D model (JSmol)
ChemSpider
  • InChI=1S/CH4O/c1-2/h2H,1H3/p+1
    Key: OKKJLVBELUTLKV-UHFFFAOYSA-O
  • C[OH2+]
Properties
CH5O+
Molar mass 33.049 g·mol−1
Related compounds
Related compounds
 Dimethyloxonium, Trimethyloxonium, Ethyloxonium, Methylammonium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

The methyloxonium ion is a protonated methanol molecule. It is a kind of oxonium ion and is the conjugate acid of methanol.

Formation

Methyloxonium is formed when methanol is treated with a superacid which add a proton.

When methanol undergoes autoprotolysis, if forms methyloxonium along with an equal amount of methoxide.

2 CH3OH → CH3OH+2 + CH3O−

Dissolving trifluoromethanesulfonic acid in methanol, produces methyloxonium triflate.

Heat of formation ΔHf° at standard conditions is 574.9 kJ/mol.

Reactions

Methyloxonium is unstable in the presence of water as it reacts:

CH3OH+2 + H2O → H3O+ + CH3OH

Methyloxonium methylates nucleophiles by displacing a hydrogen ion and releasing a water molecule:

CH3OH+2 + ArH → CH3Ar + H2O + H+

Between 100 and 300 °C, methanol in superacids forms methyloxonium ions which then methylate themselves and polymerise to yield alkanes, toluene and other aromatic hydrocarbons.

Methyloxonium forms in the interstellar medium, where it can be broken by UV light to form singlet methylene, or it can react with ethylene to form propylene.

References

  1. 1 2 3 Olah, George A. (June 1993). "Superelectrophiles". Angewandte Chemie International Edition in English. 32 (6): 767–788. doi:10.1002/anie.199307673. ISSN 0570-0833.
  2. ↑ Cassone, Giuseppe; Pietrucci, Fabio; Saija, Franz; Guyot, François; Saitta, A. Marco (2017). "One-step electric-field driven methane and formaldehyde synthesis from liquid methanol". Chemical Science. 8 (3): 2329–2336. doi:10.1039/c6sc04269d. hdl:11104/0280705. PMC 5363374. PMID 28451337.
  3. ↑ Devi Yadav, Geeta; Mishra, Manish; Singh, Surendra (August 2015). "Methyloxonium Triflate: an Efficient Catalyst for ring Opening of Epoxides with Alcohols under Ambient Conditions". Current Catalysis. 4 (2): 133–144. doi:10.2174/2211544704666150727220138.
  4. ↑ "Methyloxonium Enthalpy of Formation". Retrieved 1 November 2025.
  5. ↑ Grunwald, Ernest.; Jumper, Charles F. (July 1963). "Kinetics and Mechanism of the Proton Transfer between Methyloxonium Ion and Benzoic Acid in Methanol Solution". Journal of the American Chemical Society. 85 (14): 2051–2052. Bibcode:1963JAChS..85.2051G. doi:10.1021/ja00897a004.
  6. ↑ Mathew, Thomas; Esteves, Pierre Mothé; Prakash, G. K. Surya (10 August 2022). "Methanol in the RNA world: An astrochemical perspective". Frontiers in Astronomy and Space Sciences. 9 809928. Bibcode:2022FrASS...9.9928M. doi:10.3389/fspas.2022.809928.