S-2-Amino-5-(dimethyl­ammonio)phenyl sulfothio­ate

The title compound, C(8)H(12)N(2)O(3)S(2), has been isolated as an inter­mediate in the synthesis of methyl­ene blue dye, the best known phenothia­zine dye, and structurally characterized as a zwitterion. The crystal structure is dominated by inter­molecular N—H⋯O hydrogen bonds between the amine and sulfothio­ate groups, with graph-set motif C(9)R (2) (2)(8), involving anti­parallel chains and a centrosymmetric eight-membered ring. A hydrogen bond with graph-set motif R (2) (2)(14) between the ammonium and sulfothio­ate groups completes the two-dimensional network in the ab plane. Inter­molecular C—H⋯O hydrogen bonds are also present in the crystal.