Dithionic acid
Dithionic acid is the chemical H2S2O6. It is the doubly protonated form of the dithionate dianion (S2O6^2-) and is mainly seen in aqueous solutions. It is a very strong acid, with an estimated pKa around −3.4.
How it’s made:
- On a small scale, dithionic acid forms when sulfite is oxidized to dithionate and the solution is sufficiently acidic.
- On a larger scale, sulfur dioxide is cooled and oxidized with manganese dioxide to make manganese dithionate, which can be converted into dithionate salts by exchanging the cations.
- Concentrated dithionic acid solutions can be made by treating a solution of barium dithionate with sulfuric acid, which precipitates barium sulfate and leaves H2S2O6 in solution.
Formula and mass: H2S2O6; molar mass 162.14 g/mol.
This page was last edited on 3 February 2026, at 02:41 (CET).