4-Guanidinobenzenesulfonic acid

In the zwitterionic title compound (systematic name: 4-{[amino(inimio)methyl]amino}benzenesulfonate), C7H9N3O3S, the dihedral angle between the plane of the guanidine grouping and the benzene ring system is 44.87 (7)°. The crystal packing is stabilized by intermolecular N—H⋯O hydrogen bonds involving all the potential donors.

In the zwitterionic title compound (systematic name: 4-{[amino(inimio)methyl]amino}benzenesulfonate), C 7 H 9 N 3 -O 3 S, the dihedral angle between the plane of the guanidine grouping and the benzene ring system is 44.87 (7) . The crystal packing is stabilized by intermolecular N-HÁ Á ÁO hydrogen bonds involving all the potential donors.

Related literature
For the synthesis, see: Hofbens & Rath (1981). For the effect of guanidine salts on protein structure and their inhibitory effect on various physiological activities, see: Miyake et al. (2008).

Experimental
The title compound was synthesized by 4-aminobenzenesulfonic acid (3.5 g, 0.02 mol), 50% amino nitrile (3.5 g, 0.04 mol) and 37% hydrochloric acid (3.4 ml) in the ethanol boil point temperature for 24 h with stirring (Hofbens & Rath, 1981). The reaction mixture was reduced pressure distillation to obtain the rough solid, then dissolved in water. The solid residue was filtered and the filtrate was kept at room temperature. Colorless crystals of the title compound were obtained after a few days.
The crystal used for data collection was obtained by slow evaporation from a saturated water solution at room temperature.

Refinement
All of the H atoms were located in a difference synthesis and refined isotropically [aromatic C-H = 0.90 (2) Fig. 1. The molecular structure of (I), with atom labels and 40% probability displacement ellipsoids for non-H atoms.