Methanesulfonic acid
Methylsulfonic (MSS )
Colorless, odorless, viscous liquid
Solid or liquid
1.48 g · cm -3
19 ° C
167 ° C (13 hPa)
-1.9
Completely miscible with water, ethanol, tetrahydrofuran and dimethyl sulfoxide; 68 g / l in toluene to 12 g / L in n-hexane (at 23 ° C)
Risk
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Methanesulfonic acid (MSA, of Engl. Methanesulfonic acid) is the simplest sulfonic acid. The organic salts and esters of methanesulfonic acid as a methanesulfonate or mesylate (INN -D: mesylate) respectively.
Representation
MSA can be represented by a series of reactions on a laboratory scale; so, for example, by oxidation of methanethiol or dimethyl disulfide with chlorine, oxygen or nitric acid. The reaction of sulfur trioxide with methane is possible, but provides only very low yields.
Industrial manufacturing is done mainly by oxidation of methanethiol or dimethyl disulfide with chlorine. In addition, MSA is produced on a large scale via catalytic oxidation of dimethyl disulfide with oxygen in the air for several years.
Properties
MSA is a strong acid, its pKa value is specified with -0.6 or -1.9 probable. It is miscible with water in all proportions and can even serve as a solvent. The cryoscopic constant is 5.69 K. At normal pressure, the very difficult inflammatory MSA decomposes under air atmosphere from about 220 ° C to form carbon monoxide, carbon dioxide, sulfur trioxide and water. The vapor pressure is very low under standard conditions with 5.4265 • 10-5 hPa. MSA does not oxidize, even in high concentrations. With the acid strength is correlated to the high conductivity of aqueous MSA solutions at 20-40 weight - with 500 mS / cm, there is a maximum % and is comparable to that of inorganic acids. Because of autoprotolysis pure MSA directs the electrical current:
The observed proton transfer mechanism between the ions is comparable with that of other sulfonic acids. After a few days in air arises at 70-100 % strength approaches an MSA concentration of about 49% a. Similar to sulfuric acid acts MSA strongly dehydrating and can thus char organic substances containing hydroxyl groups. This property is due to slightly yellow-brown coloration of the MSA, which can be occasionally observed. Hot water or hot aqueous alkalies MSA does not hydrolyze. The electrochemical window of the MSA is quite wide - at an applied voltage of -1.40 V, a reduction of the acid protons takes place at 2.35 V, an oxidative decomposition of the acid. It acts only slightly corrosive and can even in a high concentration at temperatures of about 100 ° C does not dissolve the oxide layers of metals such as aluminum, titanium or niobium.
Use
MSA is used as a solvent and catalyst for various organic reactions such as Alkylation, esterification, polymerization or synthesis of heterocycles. By means of thionyl chloride it can be converted to the reactive methanesulfonyl chloride, can be converted to methanesulfonic acid ester with the hydroxy groups - the methanesulfonate anion is within the scope of nucleophilic substitutions, the much better, as less reactive leaving group dar. As part of cleaners will MSA increasingly used because they is easy to integrate due to their color and odorless. The resulting alkaline earth metal, iron and Manganmethansulfonate are highly soluble in water. As also very well solve the mercury, lead and Silbermethansulfonate in contrast to the corresponding insoluble salt and sulfuric acid salts in water, they can be used as electrolytes in methanesulfonic acid plating baths. Some basic drugs are used as salts of MSA in human medicine, such as rasagiline.
Compounds
Methanesulfonate can be obtained in many cases from the acid and the carbonate, hydroxide or oxide of each metal cation. Also possible is a production electrolytically, in which the metal is to be oxidized anodically in an MSA bath. Be prepared from the compounds of the methanesulfonate of various nitrogenous bases such as ammonia, methyl amine or 1-ethyl- 3-methylimidazolium ( EMIM, see 1-ethyl- 3- methylimidazolium chloride, EMIMCl ). The reaction with EMIM obtained an ionic liquid. The salts of the MSA are generally very soluble in water, since the formation of a stable ion grid is complicated by the univalence of the anion and the non-polar methyl radical. The latter makes it possible for both the acid and the salts thereof, to a certain extent, also to dissolve in non-polar solvents. Most methane sulfonates are stable up to about 400 ° C., then enters a thermal decomposition of the organic methyl radical. The salts are thus thermally stable than the acid itself
The anion has been investigated structurally, it has approximately C3v symmetry. It is also able to act as a complexing ligand. The classification in the spectrochemical series is based on Cl - < F ~ ~ SO3Cl - SO3F - < SO42 - < CH3SO3 - < H2O, according to the nephelauxetic order Cl - < CH3SO3 - < SO42 - < SO3Cl - SO3F ~ ~ H2O < F-. The catalytic properties of some methanesulfonate - including as chloride-free Lewis acids - are all studied for several years; so, for example, achieve lanthanide methanesulfonate positive effects in some esterification reactions.
Environmental Chemistry
MSA is an indication of the amount of sulfur emissions oceanic origin, into the atmosphere. It is thus an indication of the acidity of the atmosphere. There MSA as an intermediate product of the natural sulfur cycle in the photochemical conversion of dimethyl sulfide to sulfate aerosols.
MSA is readily biodegradable according to OECD Guideline 301 A, where carbon dioxide and sulfate formed as degradation products.