4-Chloro-N-(2-chlorophenyl)benzenesulfonamide

In the crystal structure of the title compound, C12H9Cl2NO2S, the N—C bond in the C—SO2—NH—C segment has gauche torsions with respect to the S=O bonds. The molecule is twisted at the S atom with an C—SO2—NH—C torsion angle of 57.6 (3)°. The N—H bond is syn to the ortho-chloro group in the anilino benzene ring. The two benzene rings are tilted relative to each other by 84.7 (1)°. The crystal structure features inversion dimers linked by N—H⋯O(S) hydrogen bonds. An intramolecular N—H⋯Cl hydrogen bond is also observed.

KS thanks the University Grants Commission, Government of India, New Delhi, for the award of a research fellowship under its faculty improvement program.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2731).

Comment
The sulfonamide moieties are important constituents of many biologically significant compounds. As a part of a study of the substituent effects on the structures and other aspects of this class of compounds (Gowda & Shetty, 2004;Gowda et al. , 2007Shakuntala et al., 2011), in the present work, the crystal structure of 4-chloro-N-(2-chlorophenyl)benzenesulfonamide (I) has been determined (Fig. 1). The conformation of the N-C bond in the C-SO 2 -NH-C segment is gauche with respect to the S═O bonds. The molecule is bent at the S atom with the C-SO 2 -NH-C torsion angle of 57.6 (3)°, compared to the value of -58.4 (3)° in 4-chloro-N-(3-chlorophenyl)benzenesulfonamide (II) (Shakuntala et al., 2011). The conformation of the N-H bond in the C-SO 2 -NH-C segment in (I) is syn to the ortho-chloro group in the adjacent anilino benzene ring, in contrast to the anti conformation observed between the N-H bond and the meta-chloro group in the anilino benzene ring of (II). The sulfonyl and the anilino benzene rings in (I) are tilted relative to each other by 84.7 (1)°, compared to the value of 77.1 (1)° in (II).
The structure shows simultaneous N-H···Cl intramolecular and N-H···O intermolecular H-bonding (Table 1). The crystal packing in (I) features dimeric aggregates stabilised by N-H···O(S) hydrogen bonds as shown in Fig.2.

Experimental
A solution of chlorobenzene (10 ml) in chloroform (40 ml) was treated drop wise with chlorosulfonic acid (25 ml) at 273 K.
After the initial evolution of hydrogen chloride subsided, the reaction mixture was brought to room temperature and poured into crushed ice in a beaker. The chloroform layer was separated, washed with cold water and allowed to evaporate slowly.
The residual 4-chlorobenzenesulfonylchloride was treated with 2-chloroaniline in a stoichiometric ratio and boiled for ten minutes. The reaction mixture was then cooled to room temperature and added to ice cold water (100 ml). The resultant 4-chloro-N-(2-chlorophenyl)benzenesulfonamide was filtered under suction and washed thoroughly with cold water. It was then recrystallized to constant melting point from dilute ethanol.
Colorless prisms used in X-ray diffraction studies were grown in ethanolic solution by slow evaporation at room temperature.

Refinement
The N-H atom was located in a difference map and refined with the distance restraint N-H = 0.86 ±0.02 Å. The other H atoms were positioned with idealized geometry using a riding model with C-H = 0.93 Å. All H atoms were refined with isotropic displacement parameters set to 1.2 times of the U eq of the parent atom.