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

There are two molecules in the asymmetric unit of the title compound, C15H11NO4S. The heterocyclic thiazine rings in both molecules adopt half-chair conformations with the S and N atoms displaced by 0.455 (4) and 0.254 (4) Å, respectively, in one molecule, and 0.480 (4) and 0.224 (5) Å in the other, on opposite sides of the mean planes formed by the remaining ring atoms. The crystal structure is stabilized by intermolecular N—H⋯O and C—H⋯O hydrogen bonds. In addition, intramolecular O—H⋯O interactions are also present.

There are two molecules in the asymmetric unit of the title compound, C 15 H 11 NO 4 S. The heterocyclic thiazine rings in both molecules adopt half-chair conformations with the S and N atoms displaced by 0.455 (4) and 0.254 (4) Å , respectively, in one molecule, and 0.480 (4) and 0.224 (5) Å in the other, on opposite sides of the mean planes formed by the remaining ring atoms. The crystal structure is stabilized by intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds. In addition, intramolecular O-HÁ Á ÁO interactions are also present.
The structure of the title compound is composed of two molecules, A (Fig. 1) and B (Fig. 2) in an asymmetric unit.
The bond distances and angles are as expected (Allen, 2002) and agree with the cortresponding bond distances and angles reported in closely related compounds (Siddiqui et al., 2008). The heterocyclic thiazine rings in both molecules adopt half chair conformation with atoms S and N displaced by 0.455 (4) and 0.254 (4) Å in molecule A and 0.480 (4) and 0.224 (5) Å, respectively, in molecule B, on the opposite sides from the mean planes formed by the remaining ring atoms.
The structure is stabilized by intermolecular hydrogen bonds of the types N-H···O and C-H···O. In addition, intramolecular interactions of the type O-H···O are also present consolidating the crystal packing; details have been provided in Tab. 1 and Fig. 3. It is intersing to note that N1 is involved in intermolecular and intramolecular interactions while N2 is devoid of any such interactions.
Experimental N-phenacylsaccharin (5.0 g, 16.6 mmoles) was added to a solution of sodium metal (2.7 g) in dry methanol (50 ml). The mixture was subjected to reflux for half an hour. The contents of the flask were cooled to room temperature and then poured on ice cold HCl (50 ml, 5%). Off white precipitates of the title compound were formed which were filtered off and were 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. = 429-430 K.

Refinement
Though all the H atoms could be distinguished in the difference Fourier map the H-atoms bonded to C-atoms were included at geometrically idealized positions and refined in riding-model approximation with C-H = 0.95 Å; the H-atoms bonded to N and O were allowed to refine. The U iso (H) were allowed at 1.2U eq (parent atom). The final difference map was essentially featurless.
supplementary materials sup-2 Figures Fig. 1. The molecule A of the title compound with the displacement ellipsoids plotted at 50% probability level (Farrugia, 1997).

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.