The Claus reaction is an example of comproportionation reaction (the inverse of disproportionation) involving hydrogen sulfide () and sulfur dioxide () to produce elemental sulfur and water as follows:
The Claus reaction is one of the chemical reactions involved in the Claus process used for the desulfurization of gases in the oil refinery plants and leading to the formation of solid elemental sulfur, more easy to store, transport and dispose off.