2-Benzenesulfonamidobenzoic acid

In the title compound, C13H11NO4S, the dihedral angle between the planes of the benzene ring and the carboxyl group is 13.7 (1)°. The molecular structure contains intramolecular N—H⋯O and C—H⋯O hydrogen-bonding interactions, while the crystal packing is stabilized by C—H⋯O and O—H⋯O hydrogen bonds and C—H⋯π interactions. The O—H⋯O hydrogen bonds form a cyclic dimer, with graph-set motif R 2 2(8), about a centre of symmetry.

In the title compound, C 13 H 11 NO 4 S, the dihedral angle between the planes of the benzene ring and the carboxyl group is 13.7 (1) . The molecular structure contains intramolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bonding interactions, while the crystal packing is stabilized by C-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds and C-HÁ Á Á interactions. The O-HÁ Á ÁO hydrogen bonds form a cyclic dimer, with graph-set motif R 2 2 (8), about a centre of symmetry.

Experimental
Anthranilic acid (1 g, 7.3 mmol) was dissolved in distilled water (10 ml) in a round bottom flask (25 ml). The pH of the solution was maintained at 8-9 using 1M, Na 2 CO 3 . Benzene sulfonylchloride (1.29 g, 7.3 mmol) was then added to the above solution and stirred atroom temperature until all the benzene sulfonyl chloride was consumed. On completion of the reaction the pH was adjusted 1-2, using 1 N HCl. The precipitate obtained was filtered, washed with distilled water, dried and recrystalized in methanol to yield brownish black crystals.

Refinement
All H atoms are clearly observed using the X-ray difference Fourier maps. H atoms were fixed geometrically and treated as riding, with C-H = 0.93 Å, N-H = 0.86 Å and O-H = 0.82 Å, with U iso (H) = 1.2U eq (C,N) and U iso (H) = 1.5U eq (O). Fig. 1. A view of the title compound showing the atom labelling scheme and displacement ellipsoids at the 30% probability level.

Special details
Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and tor-

sion angles
Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted Rfactors wR and all goodnesses of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.