3,8-Dimethylquinazoline-2,4(1H,3H)-dione

In the title compound, C10H10N2O2, all non-H atoms are approximately co-planar with an r.m.s. deviation of 0.016 Å. In the crystal, molecules are linked into inversion dimers by pairs of N—H⋯O hydrogen bonds. Chains along [010] are buiilt up by π–π interactions [centroid–centroid distance = 3.602 (1) Å] between the benzene and piperazine rings of adjacent molecules.

In the title compound, C 10 H 10 N 2 O 2 , all non-H atoms are approximately co-planar with an r.m.s. deviation of 0.016 Å . In the crystal, molecules are linked into inversion dimers by pairs of N-HÁ Á ÁO hydrogen bonds. Chains along [010] are buiilt up byinteractions [centroid-centroid distance = 3.602 (1) Å ] between the benzene and piperazine rings of adjacent molecules.

Comment
The title compound is the intermediate of a kind of highly potent and selective insecticide (Feng et al., 2010). Herein, we report the synthesis and crystal structure of the title compound.
In the title compound, C 10 H 10 N 2 O 2 , all non-hydrogen atoms lie on the same plane with the Rms about 0.016 Å, the largest deviation being 0.037 (1) Å for atom O2 (Figure 1).
The isolated title compound molecules are linked by N-H···O hydrogen bonds into dimers ( Figure 2, Table 1). Furthermore, the chain structures alone [010] direction are bulit up by /pi-/pi interatcions (center to center distances of 3.602 (1) Å) between the phenyl groups and piperazinyl groups of the adjacent molecules ( Figure 3).

Experimental
The title compound was synthesized as the reference method (Feng et al., 2010): To a solution of 2-amino-N,3-dimethylbenzamide (1.64 g, 1.0 mmol) in THF (20 ml), bis(trichloromethyl)-carbonate (1.0 g, 0.33 mmol) was added, and then keep stirring for 2h. After that THF was removed and water (20 ml) was added slowly. The resulting suspension was filtered, and the solids were washed with water (15 ml) and dried (yield 65%). The crystals suitable for X-ray diffraction were obtained by slow evaporation from methanol solution at room temperature for several days.

Refinement
H atoms bound to C atoms were placed in calculated positions and treated as riding on their parent atoms, with C-H = 0.93 Å (aromatic); C-H = 0.96 Å (methyl), and with U iso (H) = 1.2U eq (C), while N-bound H atom was found from Fourier-map and was freely refined. Fig. 1. The molecular structure of the title compound, showing displacement ellipsoids at the 50% probability level for non-H atoms.

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.
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 > 2sigma(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.