S-2-Amino-5-(dimethyl-ammonio)phenyl sulfothio-ate.

The title compound, C(8)H(12)N(2)O(3)S(2), has been isolated as an inter-mediate in the synthesis of methyl-ene blue dye, the best known phenothia-zine dye, and structurally characterized as a zwitterion. The crystal structure is dominated by inter-molecular N-H⋯O hydrogen bonds between the amine and sulfothio-ate groups, with graph-set motif C(9)R(2) (2)(8), involving anti-parallel chains and a centrosymmetric eight-membered ring. A hydrogen bond with graph-set motif R(2) (2)(14) between the ammonium and sulfothio-ate groups completes the two-dimensional network in the ab plane. Inter-molecular C-H⋯O hydrogen bonds are also present in the crystal.