N,N′-Bis(2-chlorophenyl)succinamide

There is one half-molecule in the asymmetric unit of the title compound, C16H14Cl2N2O2, with a center of symmetry at the mid-point of the central C—C bond. The N—H and C=O bonds in the C—NH—C(O)—C fragment are anti to each other and the amide O atom is anti to the H atoms attached to the adjacent C atoms. However, the conformation of the N—H bond in the amide fragments is syn to the ortho-chloro groups in the adjacent benzene rings. The dihedral angle between the benzene ring and the NH—C(O)—CH2 fragment is 47.0 (2)°. In the crystal, a series of N—H⋯O intermolecular hydrogen bonds link the molecules into chains along the b axis.

BSS 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: FL2341).

Comment
Amide and sulfonamide moieties are important constituents of many biologically significant compounds. As a part of studying the substituent effects on structures of this class of compounds (Gowda et al., 2000(Gowda et al., , 2007Saraswathi et al., 2011a,b), the structure of (I) has been determined ( Fig.1). (I) sits on a center of symmetry passing through the mid-point of the central C-C bond to give a half molecule per asymmetric unit. This is similar to that obseved in bis(2-chlorophenylaminocarbonylmethyl)disulfide (II) (Pierrot et al., 1984), N,N-bis(2-methylphenyl)-succinamide (III) (Saraswathi et al., 2011a) and N,N-bis(3-chlorophenyl)-succinamide (III) (Saraswathi et al., 2011b). The packing of molecules in the crystal linked by of N-H···O hydrogen bonds (Table 1) is shown in Fig. 2.

Experimental
Succinic anhydride (0.01 mol) in toluene (25 ml) was treated drop wise with 2-chloroaniline (0.01 mol) also in toluene (20 ml) with constant stirring. The resulting mixture was stirred for one hour and set aside for an additional hour at room temperature for completion of the reaction. The mixture was then treated with dilute hydrochloric acid to remove unreacted 2-chloroaniline. The resultant solid N-(2-chlorophenyl)-succinamic acid was filtered under suction and washed thoroughly with water to remove the unreacted succinic anhydride and succinic acid. The compound was recrystallized to constant melting point from ethanol. The purity of the compound was checked by elemental analysis and characterized by its infrared and NMR spectra.
The N-(2-chlorophenyl)succinamic acid obtained was then treated with phosphorous oxychloride and excess of 2chloroaniline at room temperature with constant stirring. The resultant mixture was stirred for 4 h, kept aside for additional 6 h for completion of the reaction and poured slowly into crushed ice with constant stirring. It was kept aside for a day.
supplementary materials sup-2 The resultant solid, N,N-bis(2-chlorophenyl)-succinamide was filtered under suction, washed thoroughly with water, dilute sodium hydroxide solution and finally with water. It was recrystallized to constant melting point from a mixture of acetone and chloroform. The purity of the compound was checked by elemental analysis, and characterized by its infrared and NMR spectra.
Needle like colorless single crystals used in the X-ray diffraction studies were were grown in a mixture of acetone and chloroform at room temperature.

Refinement
The H atom of the NH group was located in a difference map and later restrained to the distance N-H = 0.86 (2) Å. The other H atoms were positioned with idealized geometry using a riding model with the aromatic C-H = 0.93Å and the methylene C-H = 0.97 Å. All H atoms were refined with isotropic displacement parameters (set to 1.2 times of the U eq of the parent atom). Fig. 1. Molecular structure of (I), showing the atom labelling scheme and displacement ellipsoids are drawn at the 50% probability level.   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) 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.