Dithionous acid
# Dithionous acid

Dithionous acid is a sulfur oxoacid with the chemical formula $H_2S_2O_4.$ It is unstable in pure form, but its salts, known as dithionites, are stable.

It was initially assumed that the $C_2$ symmetric structure HOS(=O)-S(=O)OH is the most stable among molecules with the formula H $_2S$ $_2O$ $_4$ using ab initio calculations. The reason for this is the existence of intermolecular hydrogen bonds. It is now known that dithionous acid spontaneously decomposes to $SO_2$ and $S(OH)_2.$

Sodium dithionite is a white powder used as a reductant and a bleaching agent. It is also used to reduce the nitro group to an amino group in organic reactions.

