Methanedisulfonic acid

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Methanedisulfonic acid is the organosulfur compound CH2(SO3H)2, the disulfonic acid of methane. It is a very strong acid, with a predicted pKa around -0.7, similar in strength to sulfuric acid. The substance is a colorless solid that melts at 138–140°C and boils at about 209–210°C, though it decomposes if heated. It dissolves in water.

How it’s made
- It is commonly prepared by treating methanesulfonic acid with oleum (fuming sulfuric acid containing extra sulfur trioxide).
- A higher-yield method converts dichloromethane (CH2Cl2) with potassium sulfite under hot, hydrothermal conditions to a potassium salt CH2(SO3K)2, which can be acidified to give the free acid.

History
- The acid was first prepared in 1833 by Gustav Magnus as a decomposition product in early attempts to make diethyl ether from ethanol and sulfuric acid.
- It has been referred to as methionic acid in the past, and 19th-century chemists studied various sulfonic acids and their salts.
- In 1929, Hilmar Johannes Backer developed a higher-yield synthesis from dichloromethane and potassium sulfite.

Safety
- Methanedisulfonic acid is corrosive and dangerous to handle. It can cause severe skin and eye damage and may affect aquatic life. Use appropriate protective equipment and procedures.