Crystal structure of 2-[4(E)-2,6-bis(4-chlorophenyl)-3-ethylpiperidin-4-ylidene]acetamide

In the title piperidine derivative, C21H22Cl2N2O, the piperidine ring adopts a chair conformation. The chlorophenyl rings are oriented at an angle of 45.59 (14)° with respect to each other. In the crystal, molecules are linked via N—H⋯O hydrogen bonds, forming C(4) chains along [100]. The chains are linked by C—H⋯O hydrogen bonds, forming sheets parallel to the ab plane. Within the sheets, there are N—H⋯π interactions present. The crystal studied was refined as an inversion twin.


Data collection
Bruker SMART APEX CCD areadetector diffractometer 31733 measured reflections 4427 independent reflections 4220 reflections with I > 2(I) R int = 0.022
Cg is the centroid of the C1-C6 ring.

S1. Chemical context
The significance of piperidin-4-one as intermediates in the synthesis of a range of physiologically active compounds have been reviewed by (Prostakov & Gaivoronskaya, 1978). 4-piperidone derivatives were found to be superior raw materials for preparation of analgesics (Yu et al., 2002). The amide bond is one of the most important functional groups in current chemistry since amides are multipurpose synthetic intermediates used in the manufacture of several pharmacological products, polymers, detergents, lubricants, and drug stabilizers, as well as key structural motifs present in numerous natural products (Zabicky, 1970;Greenberg et al., 2000;Deopura et al., 2008;Johnsson, 2004). Usually, amides have been synthesized by the hydration of nitriles, catalyzed by strong acids (Moorthy & Singhal, 2005) and bases (Kornblum & Singaram, 1979;Katritzky et al., 1989). In view of the many interesting applications of piperidine derivatives we synthesized the title compound and report herein its crystal structure.

S2. Structural commentary
The molecular structure of the title compound is illustrated in Fig. 1

S3. Supramolecular features
In the crystal, moleculesare linked via N-H···O hydrogen bonds into C(4) chains propagating along [100] (Table 1 and Fig. 2). The chains are linked by C-H···O hydrogen bonds forming sheets parallel to the ab plane (Table 1 and Fig. 2).
Within the sheets there are N-H···π interactions present (see Table 1 and Fig. 3).

S4. Synthesis and crystallization
The title (2,6-diarylpiperidin-4-ylidene)acetonitrile was refluxed with a few drops of diluted Sulphuric acid for 30-45 mins. After completion of the reaction (monitored by TLC) the mixture was neutralized with saturated sodiumbicarbonate solution, until the disappearance of brisk effervescence. After the solid that appeared was filtered and dried. This crude product mass was purified by column-chromatography over silica-gel (100-200 mesh) using petroleum ether and ethylacetate (25%) as eluent to give the title compound. Suitable colourless block-like crystals were obtained by slow evaporation of a solution of the title compound in ethanol at room temperature.

S5. Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. Atoms H1N, H2NA and H2NB were located from a difference Fourier map and freely refined. The remaining H atoms were positioned geometrically and treated as riding on their parent C atoms: C-H = 0.93-0.98 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) for other H atoms.

Figure 1
The molecular structure of the title compound, with atom labelling. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
Crystal packing of the title compound, viewed along the c axis. The N-H···O and C-H···O hydrogen bonds are shown as dashed lines (see Table 1). For clarity H atoms not involved in these hydrogen bonds have been omitted.

Figure 3
Crystal packing of the title compound, showing the N-H···π interactions as dashed lines (see Table 1). For clarity H atoms not involved in these interactions have been omitted. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.40 e Å −3 Δρ min = −0.29 e Å −3 Absolute structure: Refined as an inversion twin Absolute structure parameter: 0.37 (7) Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.