Crystal structure of fipronil

The molecular and crystal structure of the insecticide fipronil is reported. In the crystal, N—H⋯N, N—H⋯O, C—H⋯F hydrogen bonds, C—N⋯π and C—Cl⋯π interactions link adjacent molecules, forming a three-dimensional network. In addition, there are short F⋯F interactions present.


Chemical context
Fipronil is an insecticide that belongs to the phenylpyrazole group. It is an insecticide with extended use in the control of many agricultural vermin. Fipronil contains a trifluoromethylsulfinyl substituent that is not present in any other agrochemicals and this is thought to contribute to its remarkable potency in the field (Hainzl & Casida, 1996). In addition, it is a highly effective and broad-spectrum insecticide against piercing-sucking, contact and chewing pests and is widely used to control many species of soil and foliar insects on various crops including rice, vegetables and fruits (Kaur et al., 2015). The toxicity of fipronil is attributed to its ability to act at the GABA receptor as a non-competitive inhibitor of the GABA-gated chloride channels of neurons in the central nervous system. Impediments to the influx of the chloride ions affect the transmission of nervous impulses, causing insect death by neuronal hyperexcitation and paralysis (Medeiros et al., 2015). Recently, eggs contaminated with fipronil have been found in Europe, Hong Kong and the Republic of Korea. We report here the crystal structure of fipronil, 5-amino-1-[2,6dichloro-4-(trifluoromethyl)phenyl]-4-(trifluoromethanesulfinyl)-1H-pyrazole-3-carbonitrile.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The dihedral angle between the planes of the pyrazole and benzene rings is 89.03 (9) . All bond lengths and bond angles are normal and comparable to those observed in similar crystal structures (Kang et al., 2015;Jiang & Xu, 2009).

Figure 1
The structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radius.

Figure 2
A view along the b axis of the crystal packing of the title compound. Looped chains are formed through intermolecular C-NÁ Á Á interactions together with N-HÁ Á ÁN and C-HÁ Á ÁF hydrogen bonds (yellow dashed lines). H atoms not involved in intermolecular interactions have been omitted for clarity.

Synthesis and crystallization
The title compound was purchased from Dr. Ehrenstorfer GmbH. Colourless single crystals suitable for X-ray diffraction were obtained from a CH 3 CN solution by slow evaporation at room temperature.

5-Amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethanesulfinyl])-1H-pyrazole-3-carbonitrile
Crystal data 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.