2-(3,5-Dimethyl-1,1-dioxo-2H-1λ6,2,6-thiadiazin-4-yl)benzoic acid

In the title molecule, C12H12N2O4S, the S atom of the thiadiazine ring deviates by 0.5104 (4) Å from the mean plane of the other five atoms [largest deviation = 0.0623 (15) Å] giving a slightly distorted sofa conformation. The carboxy H atom was refined as disordered over two sets of sites with refined occupancies of 0.58 (2) and 0.48 (2). This corresponds to rotational disorder of the C=O and O—H groups about the attached C—C bond. In the crystal, O—H⋯O and N—H⋯O hydrogen bonds connect the molecules into chains along [110].

In the title molecule, C 12 H 12 N 2 O 4 S, the S atom of the thiadiazine ring deviates by 0.5104 (4) Å from the mean plane of the other five atoms [largest deviation = 0.0623 (15) Å ] giving a slightly distorted sofa conformation. The carboxy H atom was refined as disordered over two sets of sites with refined occupancies of 0.58 (2) and 0.48 (2). This corresponds to rotational disorder of the C O and O-H groups about the attached C-C bond. In the crystal, O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds connect the molecules into chains along [110].

Related literature
The title compound is a phenyl acid thiadiazine derivative. For synthetic background and applications of 1,2,6-thiadiazine-1,1-dioxide derivatives, see: Wright (1964); Breining et al. (1995). For a related structure, see: Bhatt et al. (2012) Experimental Crystal data  Table 1 Hydrogen-bond geometry (Å , ). this reason we are interested in this class of compounds as potential agents in other diseases. The crystal structure of the title compound is described herein.
The molecular structure of the title compound is shown in Fig. 1. It is the second 3,5-dimethyl based structure reported with an aromatic ring at position 4 of the thiadiazine ring. Previously we have reported the phenyl ethyl and methyl ester (Bhatt et al., 2012). It is the first containing an acid functional group in the broader family of 1,2,6-thiadiazine-1,1dioxides. The S atom of the thiadiazine ring deviates by 0.5104 (4) Å from the plane of the other five atoms [largest deviation 0.0623 (15) Å] giving a slightly distorted sofa conformation. The carboxylic acid H atom was refined as disordered over two sets of sites with refined occupancies 0.58 (2)  Experimental 2-(2, 4-dioxopentan-3-yl) benzoic acid (0.072 mol) and sulfamide (0.072 mol) were dissolved in methanol (70 ml).
Anhydrous hydrogen chloride gas was bubbled into the mixture until the temperature increased to 323 K. The contents of the reaction were then refluxed for 3hrs. The reaction mixture was cooled, filtered and the filtrate was concentrated under reduced pressure. The residual solid was treated with NaOH (0.138 mol) in water (200 ml), the contents were heated at 343 K for 2.5 hrs. The reaction progress was monitored by TLC ethyl acetate/hexane (80:20 R f = 1/2). The reaction mixture was cooled and acidified using concentrated HCl to get the crude acid as an oil. To this oily residue was added a solution of methanol/ethyl acetate (10 ml) (10/90) which yielded a white colourless solid (79%). M.p.= 523 K. Crystals suitable for X-ray analysis were grown in dioxane/water at room temprature.

Refinement
All hydrogen atoms, except H1, H3 and H4, were placed in idealized positions and refined with geometric constraints [C -H = 0.95 -0.98 Å and U iso (H) = 1.2U eq (C) or 1.5U eq (C methyl ). The hydrogen atom H1 was located in a difference Fourier map and refined with O-H distance restraint to the value of 0.97 (1) Å. The carboxy hydroxyl hydrogen is distributed over two sites: H3 and H4, were both located in a difference Fourier map and refined with a O-H distance restraint to the value of 0.97 (1) Å. The site occupancy factors refined to 0.48 (8) for H3 and 0.52 (8) for H4.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at 40% probability. Atoms H3 and H4 are disorder components.

Figure 2
The hydrogen bonding interactions of the title compound along [110]. All H atoms except those involved in hydrogen bonding have been omitted for clarity. 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 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.