Disulfuric acid (alternative spelling disulphuric acid) or pyrosulfuric acid (alternative spelling pyrosulphuric acid), also named oleum, is a

sulfur oxoacid Sulfur oxoacids are chemical compounds that contain sulfur, oxygen, and hydrogen. The best known and most important industrially used is sulfuric acid. Sulfur has several oxoacids; however, some of these are known only from their salts (these are s ...

. It is a major constituent of fuming sulfuric acid, oleum, and this is how most chemists encounter it. As confirmed by

X-ray crystallography X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...

, the molecule consists of a pair of SO₂(OH) groups joined by an oxide.

Reactions

It is also a minor constituent of liquid anhydrous sulfuric acid due to the equilibria: :H2SO4<=>H2O + SO3 :SO3 + H2SO4<=> H2S2O7 :2H2SO4 <=> H2O + H2S2O7 ''Global The acid is prepared by reacting excess sulfur trioxide (SO₃) with sulfuric acid:
H2SO4 + SO3 -> H2S2O7 Disulfuric acid can be seen as the sulfuric acid

analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...

of an

acid anhydride An acid anhydride is a type of chemical compound derived by the removal of water molecules from an acid. In organic chemistry, organic acid anhydrides contain the functional group R(CO)O(CO)R'. Organic acid anhydrides often form when one equivale ...

. The mutual electron-withdrawing effects of each sulfuric acid unit on its neighbour causes a marked increase in acidity. Disulfuric acid is strong enough to protonate "normal" sulfuric acid in the (anhydrous) sulfuric acid solvent system. There are salts of disulfuric acid, commonly called pyrosulfates, e.g. potassium pyrosulfate. There are other related acids with the general formula H₂O·(SO₃)_''x'' though none can be isolated.

References

{{Hydrogen compounds Hydrogen compounds Pyrosulfates Sulfur oxoacids Acid anhydrides

Reactions

See also

References