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

The title compound, C8H12N2O3S2, 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 center dot center dot center dot 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 center dot center dot center dot O hydrogen bonds are also present in the crystal.