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.