2-(5-Bromo-3-methylsulfanyl-1-benzofuran-2-yl)acetic acid

The title compound, C11H9BrO3S, was prepared by alkaline hydrolysis of ethyl 2-(5-bromo-3-methylsulfanyl-1-benzofuran-2-yl)acetate. In the crystal structure, the carboxyl groups are involved in intermolecular O—H⋯O hydrogen bonds, which link the molecules into centrosymmetric dimers. These dimers are further packed into stacks along the c axis by weak C—H⋯π interactions. In addition, the stacked molecules exhibit a Br⋯S interaction of 3.4787 (7) Å.

The title compound, C 11 H 9 BrO 3 S, was prepared by alkaline hydrolysis of ethyl 2-(5-bromo-3-methylsulfanyl-1-benzofuran-2-yl)acetate. In the crystal structure, the carboxyl groups are involved in intermolecular O-HÁ Á ÁO hydrogen bonds, which link the molecules into centrosymmetric dimers. These dimers are further packed into stacks along the c axis by weak C-HÁ Á Á interactions. In addition, the stacked molecules exhibit a BrÁ Á ÁS interaction of 3.4787 (7) Å .
The benzofuran unit is essentially planar, with a mean deviation of 0.011 (2) Å from the least-squares plane defined by the nine constituent atoms. In crystal structure, the carboxyl groups are involved in intermolecular O-H···O hydrogen bonds  Table 1; Cg is the centroid of the C2-C7 benzene ring, symmetry code as in Fig. 2). Additionally, the stacked molecules exhibit a Br···S interaction, with a C4-Br···S iii distance of 3.4787 (7) Å (symmetry code as in Fig. 2).
Water was added, and the solution was extracted with dichloromethane. The aqueous layer was acidified to pH 1 with concentrated hydrochloric acid and then extracted with chloroform, dried over magnesium sulfate, filtered and concentrated under vacuum. The residue was purified by column chromatography (ethyl acetate) to afford the title compound as a colorless

Refinement
The H atom of O3 was positioned in a difference Fourier map and refined freely. Other H atoms were geometrically positioned and refined using a riding model, with C-H = 0.93 (aromatic), 0.97 (methylene), and 0.96 Å (methyl) H atoms, respectively, and with U iso (H) = 1.2Ueq(C) (aromatic, methylene), and 1.5Ueq(C) (methyl) H atoms.

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 > 2sigma(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.