Thiosulfuric acid

Thiosulfuric acid  is a sulfur oxoacid. The acid cannot be made by acidifying thiosulfate salts as the acid readily decomposes in water. The decomposition products can include, depending on the exact reaction conditions, sulfur, sulfur dioxide, hydrogen sulfide, polysulfanes, sulfuric acid and polythionates. Anhydrous methods of producing the acid include:
 * (in diethyl ether at -78°C )
 * H2S + SO3 → H2S2O3•nEt2O
 * Na2S2O3+2HCl → 2NaCl + H2S2O3•2Et2O

The anhydrous acid decomposes below 0°C :
 * H2S2O3 → H2S + SO3

There is an isomeric form, a white crystalline adduct, H2S.SO3 which can be prepared at low temperature.