4-{2-[(5-Chloro-2-hydroxybenzylidene)amino]ethyl}benzenesulfonamide

In the molecule of the title compound, C15H15ClN2O3S, the S atom adopts a distorted tetrahedral coordination geometry with two O atoms, one N atom of the amide group and one C atom of the aromatic ring. An intramolecular O—H⋯N hydrogen bond results in the formation of a planar six-membered ring, which is oriented with respect to the adjacent aromatic ring at a dihedral angle of 3.38 (11)°. Thus, the two rings are nearly coplanar. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into centrosymmetric dimers.

In the molecule of the title compound, C 15 H 15 ClN 2 O 3 S, the S atom adopts a distorted tetrahedral coordination geometry with two O atoms, one N atom of the amide group and one C atom of the aromatic ring. An intramolecular O-HÁ Á ÁN hydrogen bond results in the formation of a planar sixmembered ring, which is oriented with respect to the adjacent aromatic ring at a dihedral angle of 3.38 (11) . Thus, the two rings are nearly coplanar. In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into centrosymmetric dimers.

Comment
The significance of sulfonamide was realised when sulfanilamide was first time reported as antibacterial drug. Later on, many sulfanilamide derivatives were synthesized, characterized and tested for antibacterial, anti-tumour, anti-carbonic anhydrase (Supuran & Scozzafava 2001), diuretic, hypoglycemic, anti-thyroid or protease inhibitory activity. Thus, sulfanilamide is performing a leading role for the development and expansion of all other types of medicinally important sulfonamides (Chohan & Shad, 2007).
In the molecule of (I), S1 atom has a distorted tetrahedral coordination completed by the two O atoms, one N atom of amide group and one C atom of the adjacent aromatic ring B (C10-C15) ( Table 1 (Table 2) results in the formation of a planar six-membered ring C (O1/H1/N1/C7/C1/C2), which is oriented with respect to the aromatic rings at dihedral angles of A/C = 3.38 (11)° and B/C = 22.33 (13)°. So, rings A and C are also nearly coplanar.
In the crystal structure, intermolecular N-H···O hydrogen bonds (Table 2) link the molecules into centrosymmetric dimers (Fig. 2), in which they seem to be effective in the stabilization of the structure.

Experimental
For the preparation of the title compound, an ethanol solution (15 ml) of 4-(2-aminoethyl)benzenesulfonamide (400.5 mg, 2 mmol) was added to an ethanol solution (10 ml) of 5-chlorosalicylaldehyde (313.1 mg, 2 mmol). The reaction mixture was refluxed for 3 h. The colour of the solution gradually changed from colorless to greenish yellow. The solution was cooled to room temperature, filtered and the volume was reduced to about one-third on the rotary evaporator. It was allowed to stand for 10 d, bright yellow crystals of the title compound were obtained (m.p. 441 K).  Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.