Hyposulfite, SO22−, was reported as a sulfur oxyanion. However salts containing SO22− and the corresponding acid, hyposulfurous acid (H2SO2) are not believed to exist.[1]
However, there are also some reports about hyposulfites. Metallic zinc can react with sulfuryl chloride, producing zinc hyposulfite[2]:
The brown crystal cobalt hyposulfite can be produced by mixing up cobalt(II) acetate and sodium dithionite in water, adding superfluous ammonia, and then inletting carbon dioxide[2]:
The word hyposulfite is also a synonym for the thiosulfate ion, S2O32−.
As opposed to hydrosulfite which is a synonym for the dithionite ion, S2O42−.