Methanesulfonic Acid
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Methanesulfonic acid (MsOH, MSA) or methanesulphonic acid (in British English) is an organosulfuric, colorless liquid with the molecular formula and
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such as ...
. It is the simplest of the alkylsulfonic acids (). Salts and
ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s of methanesulfonic acid are known as mesylates (or methanesulfonates, as in ethyl methanesulfonate). It is
hygroscopic Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption (chemistry), absorption or adsorption from the surrounding Natural environment, environment, which is usually at normal or room temperature. If water mol ...
in its concentrated form. Methanesulfonic acid can dissolve a wide range of metal salts, many of them in significantly higher
concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...
s than in hydrochloric acid (HCl) or
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...
().


History and synthesis


Early history

German chemist Hermann Kolbe discovered MSA between 1842 and 1845 and originally termed it methyl hyposulphuric acid. The discovery stemmed from earlier work by Berzelius and Marcet in 1813, who treated carbon disulfide with moist
chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
and produced a compound they named "sulphite of chloride of carbon". By reacting it with barium hydroxide Kolbe demonstrated it to actually be trichloromethylsulfonyl chloride (CCl₃SO₂Cl in modern notation). From resulting barium trichloromethylsulfonate Kolbe isolated the free acid, which he was then able to sequentially dechlorinate by electrolytically generated atomic hydrogen to ultimately yield MSA. Kolbe's research on methanesulfonic and chloroacetic acids was hailed by Berzelius as strong evidence for his theory of copulated compounds, a modification of radical theory to accommodate substitution reactions which posited the combination of organic and inorganic moieties without significantly altering the properties of the latter. Later in the 19th century, the name transitioned to methyl sulphonic acid. Other historical laboratory synthesis routes included oxidizing methanethiol, dimethyl disulfide or methyl thiocyanate with
nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
.


Industrial production

The first commercial production of MSA, developed in the 1940s by Standard Oil of Indiana, was based on oxidation of dimethylsulfide by from air. Although inexpensive, this process suffered from a poor product quality and explosion hazards. Starting from the 1960s, it received a shortened name of mesylic acid after the term for the " mesyl" group coined by Helferich et al. in 1938. In 1967, the Pennwalt Corporation (USA) developed a different process for dimethylsulfide (as a water-based emulsion) oxidation using
chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...
, followed by extraction-purification. In 2022 this chlorine-oxidation process was used only by
Arkema Arkema S.A. is a Public company, publicly listed, multi-national manufacturer of specialty materials, headquartered in La Défense, near Paris, France. It has three specialty materials segments (or divisions); Adhesive, adhesives, advanced mater ...
(France) for making high-purity MSA. This process is not popular on a large scale, because it co-produces large quantities of hydrochloric acid. Between years 1970 and 2000 MSA was used only on a relatively small-scale in niche markets (for example, in the microelectronic and electroplating industries since the 1980s), which was mainly due to its rather high price and limited availability. However, this situation changed around 2003, when
BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...
launched commercial production of MSA in
Ludwigshafen Ludwigshafen, officially Ludwigshafen am Rhein (; meaning "Ludwig I of Bavaria, Ludwig's Port upon the Rhine"; Palatine German dialects, Palatine German: ''Ludwichshafe''), is a List of cities and towns in Germany, city in the German state of Rh ...
based on a modified version of the aforementioned air oxidation process, oxidising dimethyldisulfide with
nitric acid Nitric acid is an inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but samples tend to acquire a yellow cast over time due to decomposition into nitrogen oxide, oxides of nitrogen. Most com ...
which is then restored using atmospheric oxygen. The former is produced in one step from
methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical compound and the simplest aliphatic Alcohol (chemistry), alcohol, with the chemical formula (a methyl group linked to a hydroxyl group, often ab ...
from syngas,
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
. An even better (lower-cost and environmentally friendlier) process of making methanesulfonic acid was developed in 2016 by Grillo-Werke AG (Germany). It is based on a direct reaction between
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...
and oleum at around 50 °C and 100 bar in the presence of a potassium persulfate initiator. Further addition of sulfur trioxide gives methanedisulfonic acid instead. This technology was acquired and commercialized by
BASF BASF SE (), an initialism of its original name , is a European Multinational corporation, multinational company and the List of largest chemical producers, largest chemical producer in the world. Its headquarters are located in Ludwigshafen, Ge ...
in 2019.


Applications

Since ca. 2000 methanesulfonic acid has become a popular replacement for other acids in numerous industrial and laboratory applications, because it: * is a strong acid, * has a low
vapor pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...
(see boiling points in the "Properties" inset), * is not an
oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ''electr ...
or explosive, like nitric, sulfuric or perchloric acids. * is a liquid at room temperature, * is soluble in many organic solvents, * forms water-soluble salts with all inorganic cations and with most organic cations, * does not form complexes with metal ions in water, * its anion, mesylate, is non-toxic and suitable for pharmaceutical preparations. The closely related ''p''-toluenesulfonic acid (PTSA) is solid. 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 DMSO, the complex of BH3 and the solvent is formed.


Applications

Solutions of methanesulfonic acid are used for the electroplating of tin and tin-lead solders. It is displacing the use of fluoroboric acid, which releases corrosive and volatile
hydrogen fluoride Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with chemical formula . It is a very poisonous, colorless gas or liquid that dissolves in water to yield hydrofluoric acid. It is the principal industrial source of fluori ...
. Methanesulfonic acid is also a primary ingredient in rust and scale removers. It is used to clean off surface rust from ceramic, tiles and porcelain which are usually susceptible to acid attack.


See also

* Trifluoromethanesulfonic acid, the more acidic trifluoro analogue


References

{{Authority control Sulfonic acids Reagents for organic chemistry Acid catalysts Organic compounds with 1 carbon atom Methyl compounds