2-Methyl-3,5-dinitrobenzoic acid

In the title compound, C8H6N2O6, the O atoms of the nitro groups, the methyl H atoms and the carboxyl C=O and C—OH groups are disordered over two sets of sites with an occupancy ratio of 0.595 (16):0.405 (16). In the crystal, inversion dimers linked by pairs of O—H⋯O hydrogen bonds arise for both carboxyl disorder components and C—H⋯O bonds and weak C—H⋯π interactions consolidate the packing.

In the title compound, C 8 H 6 N 2 O 6 , the O atoms of the nitro groups, the methyl H atoms and the carboxyl C=O and C-OH groups are disordered over two sets of sites with an occupancy ratio of 0.595 (16):0.405 (16). In the crystal, inversion dimers linked by pairs of O-HÁ Á ÁO hydrogen bonds arise for both carboxyl disorder components and C-HÁ Á ÁO bonds and weak C-HÁ Á Á interactions consolidate the packing.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB5136).

Comment
Isocoumarins are secondary metabolites, derived from acetate pathway, which are structurally related to coumarins but with inverted lactone ring. Isocoumarins shows a wide range of applications and biological activities including anti-cancer (Varanda et al., 2004), anti-tumor (Hill et al., 1986) etc.
The title compound (I, Fig. 1) is an intermediate towards the synthesis of substituted homophthallic acid that is a precursor for the synthesis of isocoumarins.
The O-atoms of nito groups are disordered over two sets of sites with occupancy ratio of 0.595 (16) The molecules are stabilized due to H-bondings and C-H···π interactions (Table 1).

Experimental
HNO 3 (28.0 g, 0.7 mol) was added as drops to an ice-chilled (273 K) solution of o-toluic acid (13.6 g, 0.1 mol) in H 2 SO 4 (110.4 g, 11.2 mol) with constant stirring. The reaction mixture was stirred for 15 minutes, left overnight on stirring at room temperature and then refluxed at 373 K for 4 h. More HNO 3 (21.0 g, 0.69 mol) was added after cooling to room temperature and refluxed for further 3 h. The reaction mixture was cooled to room temperature and poured to ice. The precipitates were filtered, washed with distilled water to remove free sulfates and nitrates. Recrystallization from methanol/water (1:1) afforded yellow needles of (I) suitable for x-ray diffraction. Yield 92%.

Refinement
The O-atoms of NO 2 groups along with H-atoms of CH 3 and OH groups are disordered. The coordinates of H-atoms of hydroxy group were refined.  Fig. 1. View of (I) with the atom numbering scheme having atoms of greater occupancy ratio. The displacement ellipsoids are drawn at the 30% probability level. H-atoms are shown by small circles of arbitrary radii. Fig. 2. View of (I) with the atom numbering scheme having atoms of smaller occupancy ratio. The displacement ellipsoids are drawn at the 30% probability level. H-atoms are shown by small circles of arbitrary radii. Fig. 3. The partial packing of (I), which shows that molecules form inversion dimers.