6-Chloro-8-methyl-4H-3,1-benzoxazine-2,4(1H)-dione

The two molecules in the asymmetric unit of the title compound, C9H6ClNO3, are nearly planar, with r.m.s. deviations of 0.034 and 0.037 Å. The crystal structure is stabilized by two weak intermolecular N—H⋯O interactions.

The two molecules in the asymmetric unit of the title compound, C 9 H 6 ClNO 3 , are nearly planar, with r.m.s. deviations of 0.034 and 0.037 Å . The crystal structure is stabilized by two weak intermolecular N-HÁ Á ÁO interactions.
The title compound is a nearly planar molecule (Fig. 1). The bond distances are consistent with an aromatic system.
There are two molecules in the asymmetric unit of the title compound. The molecular structure is stabilized by two weak intermolecular N-H···O interactions resulting in the formation of dimers.

Experimental
The isatoic anhydride was prepared by reaction of anthranilic acid with triphosgene in good yield (Coppola, 1980). The title compound (0.2 g) was dissolved in ethanol (50 ml) at room temperature. Colourless blocks of (I) were obtained through slow evaporation after two weeks.

Refinement
The H atoms were placed at calculated positions, with C-H = 0.93-0.98 Å, and refined as riding with Uiso(H) = 1.2-1.5Ueq(C). Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids and atom-numbering scheme.

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 > 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.