5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxylic acid

The asymmetric unit of the title compound, C17H11Cl3N2O2, contains two independent molecules; the pyrazole rings are oriented with respect to the chlorophenyl and dichlorophenyl rings at dihedral angles of 43.00 (3) and 65.06 (4)°, respectively, in one molecule, and 51.17 (3) and 69.99 (3)°, respectively, in the other. Pairs of intermolecular O—H⋯O hydrogen bonds link the molecules into dimers. In the crystal structure, there are π–π contacts between the pyrazole rings and dichlorophenyl rings [centroid–centroid distances = 3.859 (3) and 3.835 (3) Å].

The asymmetric unit of the title compound, C 17 H 11 Cl 3 N 2 O 2 , contains two independent molecules; the pyrazole rings are oriented with respect to the chlorophenyl and dichlorophenyl rings at dihedral angles of 43.00 (3) and 65.06 (4) , respectively, in one molecule, and 51.17 (3) and 69.99 (3) , respectively, in the other. Pairs of intermolecular O-HÁ Á ÁO hydrogen bonds link the molecules into dimers. In the crystal structure, there arecontacts between the pyrazole rings and dichlorophenyl rings [centroid-centroid distances = 3.859 (3) and 3.835 (3) Å ].

Related literature
For bond-length data, see: Allen et al. (1987). For the chemical background, see: Tang et al. (2007).
The asymmetric unit of the title compound contains two crystallographically independent molecules (Fig. 1). The bond lengths (Allen et al., 1987) (Table 1) link the molecules (Fig. 1), in which they may be effective in the stabilization of the structure.

S2. Experimental
For the preparation of the title compound, 2,4-dichlorophenylhydrazine hydrochloride (13.3 g) diluted in ethanol (20 ml) is added to ethyl 4-(4-chlorophenyl)-3-methyl-2,4-dioxobutanoate (17.6 g) diluted in toluene (50 ml) and the mixture is stirred for 18 h at room temperature. Without isolating the hydrazone, paratoluenesulfonic acid (0.56 g) is added, and the ternary azeotrope (water, ethanol, toluene) is distilled. Toluene reflux is continued for 1 h and the reaction mixture is cooled to room temperature. The insoluble material is filtered off. The solvents are removed under reduced pressure to give an oil. KOH (8.1 g) in pellets are added to a solution of the oil obtained in the previous step in MeOH (100 ml). The mixture is left for 1 h at room temperature and the solvents are decanted into water (200 ml) at 333 K. Hydrochloric acid is then added to the aqueous phase until pH = 1.5. The colorless crystals formed are filtered off, washed with water and dried under vaccum to give the expected product (yield; 9.9 g). Crystals suitable for X-ray analysis were obtained by slow evaporation of an acetic acid solution.  The molecular structure of the title molecule, with the atom-numbering scheme.

5-(4-Chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxylic acid
Crystal data Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. 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 R-factors(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.