3-Benzoyl-4-hydroxy-2-methyl-2H-1,2-benzothiazine 1,1-dioxide

In the title molecule, C16H13NO4S, the heterocyclic thiazine ring adopts a half-chair conformation with the S and N atoms displaced by 0.410 (3) and 0.299 (3) Å, respectively, on opposite sides of the mean plane formed by the remaining ring atoms. The crystal structure is stabilized by intermolecular hydrogen bonds of the types O—H⋯O and C—H⋯O; the former result in dimers lying about inversion centers and the latter form chains of molecules running along the c axis. In addition, intramolecular O—H⋯O links are present.

In the title molecule, C 16 H 13 NO 4 S, the heterocyclic thiazine ring adopts a half-chair conformation with the S and N atoms displaced by 0.410 (3) and 0.299 (3) Å , respectively, on opposite sides of the mean plane formed by the remaining ring atoms. The crystal structure is stabilized by intermolecular hydrogen bonds of the types O-HÁ Á ÁO and C-HÁ Á ÁO; the former result in dimers lying about inversion centers and the latter form chains of molecules running along the c axis. In addition, intramolecular O-HÁ Á ÁO links are present.
In the title compound ( Fig. 1), the bond distances and angles agree with the cortresponding bond distances and angles reported in closely related compounds (Siddiqui et al., 2008;Ahmad, Siddiqui, Rizvi et al., 2010). The heterocyclic thiazine ring adopts half chair conformation with atoms S1 and N1 displaced by 0.410 (3)

Experimental
An aqueous sodium hydroxide solution (1.33 g in 10 ml water) was slowly added to a solution of 3-benzoyl-4-hydroxy-2H-1,2-benzothiazine 1,1-dioxide (5.0 g, 16.6 mmole) in acetone (50 ml). Dimethylsulfate (4.03 g, 32 mmole) was added drop wise and the mixture was stirred for 30 minutes. The contents of the flask were acidified to pH 3.0 by the addition of 5% HCl. White precipitates of the title compound were formed which were collected and washed with excess distilled water. Crystals suitable for crystallographic study were grown from a solution of chloroform/methanol (4:1); yield = 3.5 g, 70%; m.p. = 420-421 K.

Refinement
Though all the H atoms could be distinguished in the difference Fourier map the H-atoms were included at geometrically idealized positions and refined in riding-model approximation with O-H = 0.84 Å and C-H = 0.95 and 0.98 Å for aryl and methyl H-atoms, respectively. The U iso (H) were allowed at 1.2U eq (O/C). The final difference map was essentially featurless.

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.