2,3-Dimethyl-6-nitroquinoxaline

The asymmetric unit of the title quinoxaline compound, C10H9N3O2, contains two crystallographically independent molecules (A and B). The quinoxaline ring systems are essentially planar, with maximum deviations of 0.006 (1) and 0.017 (1) Å, respectively, for molecules A and B. In molecule A, the dihedral angle formed between the quinoxaline ring system and nitro group is 10.94 (3)° [6.31 (13)° for molecule B]. In the crystal, molecules are linked into chains propagating along [001]: one forms zigzag chains linked by C—H⋯O hydrogen bonds, whilst the other forms ladder-like chains by way of C—H⋯N and C—H⋯O hydrogen bonds. The packing is further consolidated by weak π–π interactions [range of centroid–centroid distances = 3.5895 (7)–3.6324 (7) Å].


Comment
The direct condensation of various benzene-1,2-diamines with 1,2-dicarboxyl compounds has been successfully achieved in excellent yields using (NH 4 Cl-CH 3 OH) catalyst system at room temperature (Darabi et al., 2008). Here in this study our method comprises the synthesis of the title compound by the reaction of 4-nitro-o-phenylenediamine and butanedione in distilled water. The procedure can be performed for a broad scope of quinoxaline derivatives and is eco-friendly.
The asymmetric unit of the title quinoxaline compound comprises of two crystallographically independent 2,3-dimethyl-6-nitroquinoxaline molecules, designated molecules A and B (Fig. 1). The two independent molecules having closely similar geometries, as shown in the superposition of the non-H atoms of molecules A and B (Fig. 2) using XP in SHELXTL (Sheldrick, 2008), giving an r.m.s. deviation of 0.116 Å.
In each molecule, the quinoxaline ring system (C1-C8/N1/N2) is essentially planar, with maximum deviations of -0.006 (1) and -0.017 (1) Å, respectively, for atoms C1A of molecule A and C3B of molecule B. There are slight inclinations between the quinoxaline ring systems and nitro groups, as indicated by the dihedral angles formed of 10.94 (3) and 6.31 (13)°, respectively, for molecules A and B. The bond lengths and angles are comparable to those observed in the reported quinoxaline structures (Ghalib et al., 2010;Wozniak et al., 1993).

Experimental
The title compound was synthesized as reported in the literatures (Darabi et al., 2009;Ajaikumar & Pandurangan, 2009). A mixture of 4-nitro-o-phenylenediamine (1.5310 g) and butanedione (0.8775 g) in molar ratio 1:1 were refluxed in distilled water for 1 h. The reaction mixture was dried on rota vapor at low pressure and then recrystallized with a 1:1 mixture of alcohol-chloroform to afford brownish crystals of the title compound (1.76 g, M.p. 406 K).
supplementary materials sup-2 Refinement All H atoms were placed in their calculated positions, with C-H = 0.93 or 0.96 Å, and refined using a riding model, with U iso = 1.2 or 1.5 U eq (C). The rotating group model is applied to the methyl groups. Fig. 1. The molecular structure of (I) showing 30 % probability displacement ellipsoids for non-H atoms.  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.

Figures
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.