Disulfurous acid, metabisulfurous acid or pyrosulfurous acid is an oxoacid of sulfur with the formula . Its structure is . The salts of disulfurous acid are called disulfites or metabisulfites. Disulfurous acid is, like sulfurous acid, a phantom acid, which does not exist in the free state.[1] In contrast to disulfate, disulfite has two directly connected sulfur atoms. The oxidation state of the sulfur atom bonded to three oxygen atoms is +5 and its valence is 6, while that of the other sulfur is +3 and 4 respectively.