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 Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant c ...

. It is a major constituent of fuming sulfuric acid,

oleum Oleum (Latin ''oleum'', meaning oil), or fuming sulfuric acid, is a term referring to solutions of various compositions of sulfur trioxide in sulfuric acid, or sometimes more specifically to disulfuric acid (also known as pyrosulfuric acid). Ol ...

, and this is how most chemists encounter it. As confirmed by

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

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

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It is also a minor constituent of liquid anhydrous

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, ...

due to the equilibria: : : : The acid is prepared by reacting excess

sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most conomicallyimportant sulfur oxide". It is prepared on an industrial scale as a precursor to ...

(SO₃) with sulfuric acid: : Disulfuric acid can be seen as the sulfuric acid 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 . Organic acid anhydrides often form when one equivalent of wa ...

. 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 Potassium pyrosulfate, or potassium disulfate, is an inorganic compound with the chemical formula K2S2O7. Production Potassium pyrosulfate is obtained by the thermal decomposition of other salts, most directly from potassium bisulfate: : 2 KHSO4 ...

. There are other related acids with the general formula H₂O·(SO₃)_''x'' though none can be isolated.

References

{{Hydrogen compounds Chalcogen oxoacids Pyrosulfates Sulfur oxoacids Acid anhydrides

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See also

References