Methanesulfonic acid

Methanesulfonic acid

Names
IUPAC name Methanesulfonic acid
Other names Methylsulfonic acid, MSA
Identifiers
CAS Number	75-75-2
ChEBI	CHEBI:27376
ChemSpider	6155
EC Number	200-898-6
Jmol 3D model	Interactive image
PubChem	6395
UNII	12EH9M7279
InChI InChI=1S/CH4O3S/c1-5(2,3)4/h1H3,(H,2,3,4) Key: AFVFQIVMOAPDHO-UHFFFAOYSA-N InChI=1/CH4O3S/c1-5(2,3)4/h1H3,(H,2,3,4)/f/h2H InChI=1/CH4O3S/c1-5(2,3)4/h1H3,(H,2,3,4) Key: AFVFQIVMOAPDHO-UHFFFAOYAS
SMILES O=S(=O)(O)C
Properties
Chemical formula	CH4O3S
Molar mass	96.10 g·mol^−1
Density	1.48 g/cm^3
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
Acidity (pKa)	−1.9[1]
Hazards
Safety data sheet	Oxford MSDS
EU classification (DSD)	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 (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 sulphuric acid.^[2]

Applications

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.^[3]

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.^[2] Methanesulfonic acid is also the electrolyte of choice in zinc-cerium (see cerium(III) methanesulfonate) and lead-acid (methanesulfonate) flow batteries.

Methanesulfonic acid is also a primary ingredient in rust and scale removers. ^[4] It is used to clean off surface rust from ceramic, tiles and porcelain which are usually susceptible to acid attack.

References

1. Guthrie, J. P. Hydrolysis of esters of oxy acids: pK_a values for strong acids. Can. J. Chem. 1978, 56, 2342-2354.
2. 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.
3. 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.
4. http://prep-productions.com/msds/marathon_scale_and_rust_remover.pdf