2-(4-Bromobenzenesulfonamido)acetic acid

The title compound, C8H8BrNO4S, a halogenated sulfonamide, was prepared by basic hydrolysis of the methyl ester. In the crystal, molecules form centrosymmetric hydrogen-bonded dimers via the carboxyl groups. These dimers are further linked by N—H⋯O interactions involving the carbonyl O and amide H atoms, forming a ribbon-like structure propagating in [010]. These ribbons are further linked via C—H⋯O interactions, forming a three-dimensional network.

The title compound, C 8 H 8 BrNO 4 S, a halogenated sulfonamide, was prepared by basic hydrolysis of the methyl ester. In the crystal, molecules form centrosymmetric hydrogenbonded dimers via the carboxyl groups. These dimers are further linked by N-HÁ Á ÁO interactions involving the carbonyl O and amide H atoms, forming a ribbon-like structure propagating in [010]. These ribbons are further linked via C-HÁ Á ÁO interactions, forming a three-dimensional network.
MNA acknowledges the Higher Education Commission of Pakistan for providing a PhD Scholarship under PIN 042-120607-PS2-183.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: TK2493). The title compound, (I), was prepared by basic hydrolysis of methyl (4-bromobenzenesulfonamido)acetate (II) (Arshad et al., 2008b), in a continuation of our studies on the synthesis of thiazine related heterocycles (Arshad et al., 2008c).
The molecular structure of (I), Fig. 1, reveals the bond lengths and angles are similar to those found for compounds (II), (III) and (IV).
The presence of the carboxylic acid group leads to the formation of characteristic O-H···O hydrogen-bonded centrosymmetric dimers (Table 1 and Fig. 2). These dimers are linked via N1-H1···O4 interactions, involving the carbonyl O-atom and the H-atom of the amido group, to form a ribbon-like structure propagating in the [010] direction (Table 1 and Fig. 2).
The ribbons are further linked by C-H···O interactions to form a 3-D network (Table 1 and Fig. 3).
It is interesting to compare the hydrogen bonding patterns in the three acids; (I), (III) and (IV). The formation of the hydrogen bonded carboxylic acid dimers is the same in all three compounds, i.e. R 2 2 (8) (Bernstein et al., 1995). The N-H···O hydrogen-bonding involves the sulfonamido groups in (III) and (IV) [R 2 2 (8)], while in (I) it involves the carbonyl O-atom (O4) and the H-atom of the amido group (Table 1). This leads to a larger hydrogen-bonded ring of the form [R 2 2 (10)], as shown in Fig. 4.

Experimental
Methyl (4-bromobenzenesulfonamido)acetate(II) (Arshad et al., 2008b) (1.0 g, 3.247 mmol) was dissolved in an aqueous sodium hydroxide solution (10%, 10 ml). The resulting solution was refluxed for an hour. The reaction mixture was then cooled to room temperature and acidified with 1 N HCl. A white precipitate was obtained. This was filtered off, washed with distilled water and dried. Crystals were obtained by recrystallization from methanol.

Refinement
The H-atoms were included in calculated positions and treated as riding atoms: O-H = 0.82 Å, N-H = 0.86 Å, C-H = 0.93 -0.97 Å, with U iso (H) = k × U eq (parent O-, N-or C-atom), where k = 1.5 for OH, and 1.2 for N-and C-bound H-atoms.
The maximum and minimum residual electron density peaks of 1.15 and -0.38 eÅ -3 , respectively, were located at 1.10 Å and 0.78 Å, respectively, from atom Br1.  Fig. 1. The molecular structure of (I), with displacement ellipsoids drawn at the 50% probability level.  Table 1 for details; H atoms not 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 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq