A mesoionic pyridazinium sulfonate; an unexpected reaction product

The title compound is an «inner» salt: 6-(hydroxyiminomethyl)-4-methyl-1-phenylpyridazinium-3-sulfonate, C 12 H 11 N 3 O 4 S (1). The pyridazinium ring is almost planar and twisted approximately 50 o out of the benzene ring plane. The oxime -OH group forms an intermolecular hydrogen bond to one of the sulfonate O atoms. The identification of (1) has revealed an unusual rearrangement