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Methanesulfonic acid (MsOH) is a colorless liquid with the chemical formula CH3SO3H. It is the simplest of the alkylsulfonic acids. Salts and esters of methanesulfonic acid are known as mesylates (or methanesulfonates, as in ethyl methanesulfonate). It is hygroscopic in its concentrated form. Methanesulfonic acid may be considered an intermediate compound between sulfuric acid (H2SO4), and methylsulfonylmethane ((CH3)2SO2), effectively replacing an –OH group with a –CH3 group at each step. This pattern can extend no further in either direction without breaking down the –SO2– group. Methanesulfonic acid can dissolve a wide range of metal salts, many of them in significantly higher concentrations than in hydrochloric or sulfuric acid.[3]

Methanesulfonic acid
Structural formula of methanesulfonic acid
Ball-and-stick model of methanesulfonic acid
IUPAC name
Methanesulfonic acid
Other names
Methylsulfonic acid, MSA
3D model (JSmol)
ECHA InfoCard 100.000.817
EC Number 200-898-6
Molar mass 96.10 g·mol−1
Appearance Clear liquid
Density 1.48 g/cm3
Melting point 17 to 19 °C (63 to 66 °F; 290 to 292 K)
Boiling point 167 °C (333 °F; 440 K) at 10 mmHg, 122 °C/1 mmHg
Solubility Miscible with methanol, diethyl ether.
Immiscible with hexane
log P -2.424[1]
Acidity (pKa) −1.9[2]
Safety data sheet Oxford MSDS
Harmful (Xn), Corrosive (C)
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


Methanesulfonic acid is used as an acid catalyst in organic reactions because it is a non-volatile, strong acid that is soluble in organic solvents. Methanesulfonic acid is convenient for industrial applications because it is liquid at ambient temperature, while the closely related p-toluenesulfonic acid (PTSA) is solid. However, in a laboratory setting, solid PTSA is more convenient.

Methanesulfonic acid can be used in the generation of borane (BH3) by reacting methanesulfonic acid with NaBH4 in an aprotic solvent such as THF or DMS, the complex of BH3 and the solvent is formed.[4]

Methanesulfonic acid is considered a particularly suitable supporting electrolyte for electrochemical applications, where it stands as an environmentally friendly alternative to other acid electrolytes used in plating processes.[3] Methanesulfonic acid is also the electrolyte of choice in zinc-cerium (see cerium(III) methanesulfonate), lead-acid (methanesulfonate) and some vanadium-cerium[5] flow batteries.

Methanesulfonic acid is also a primary ingredient in rust and scale removers.[6] It is used to clean off surface rust from ceramic, tiles and porcelain which are usually susceptible to acid attack.

The methylsulfonic acid sidechain was utilized in pharmaceutical products Novalgin (metamizole) & Methaniazide.


  1. ^ Towler, Christopher S.; Li, Tonglei; Wikström, Håkan; Remick, David M.; Sanchez-Felix, Manuel V.; Taylor, Lynne S. (December 2008). "An Investigation into the Influence of Counterion on the Properties of Some Amorphous Organic Salts". Molecular Pharmaceutics. 5 (6): 946–955. doi:10.1021/mp8000342.
  2. ^ Guthrie, J. Peter (September 1978). "Hydrolysis of esters of oxy acids: pKa values for strong acids; Brønsted relationship for attack of water at methyl; free energies of hydrolysis of esters of oxy acids; and a linear relationship between free energy of hydrolysis and pKa holding over a range of 20 pK units". Canadian Journal of Chemistry. 56 (17): 2342–2354. doi:10.1139/v78-385.
  3. ^ a b Gernon, M. D.; Wu, M.; Buszta, T.; Janney, P. (1999). "Environmental benefits of methanesulfonic acid: comparative properties and advantages". Green Chemistry. 1 (3): 127–140. doi:10.1039/a900157c.
  4. ^ Lobben, Paul C.; Leung, Simon Shun-Wang; Tummala, Srinivas (2004). "Integrated Approach to the Development and Understanding of the Borane Reduction of a Carboxylic Acid". Org. Proc. Res. Dev. 8: 1072. doi:10.1021/op049910h.
  5. ^ Sankarasubramanian, Shrihari; Zhang, Yunzhu; Ramani, Vijay (2019). "Methanesulfonic acid-based electrode-decoupled vanadium–cerium redox flow battery exhibits significantly improved capacity and cycle life". Sustainable Energy & Fuels. 3 (9): 2417–2425. doi:10.1039/C9SE00286C. ISSN 2398-4902.
  6. ^