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

The title compound, C11H9FO3S, was prepared by alkaline hydrolysis of ethyl 2-(5-fluoro-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 b axis by intermolecular C—H⋯O and C—H⋯F interactions.

The title compound, C 11 H 9 FO 3 S, was prepared by alkaline hydrolysis of ethyl 2-(5-fluoro-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 b axis by intermolecular C-HÁ Á ÁO and C-HÁ Á ÁF interactions.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: RN2061).
The benzofuran unit is essentially planar, with a mean deviation of 0.005 (1) Å from the least-squares plane defined by the nine constituent atoms. In the crystal structure, the carboxyl groups are involved in intermolecular O-H···O hydrogen bonds (Table 1 and Fig. 2), which link the molecules into centrosymmetric dimers. These dimers are further packed into stacks along the b axis by intermolecular C-H···O and C-H···F interactions; the first between an H atom of benzofuran ring and the C═O unit, with C6-H6···O3 i and C6-H6···O3 ii , the second between a methyl H atom of methylsulfanyl group and the fluorine atom of the benzofuran ring, with C11-H11B···F iv and C11-H11B···F v , respectively (Table 1 and 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 solid [yield 84%, m.p. 438-439 K; R f = 0.6 (ethyl acetate)]. Single crystals suitable for X-ray diffraction were prepared by evaporation of a solution of the title compound in benzene at room temperature.

Refinement
The H atom of O2 was positioned in a difference Fourier map and refined freely. The other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93 Å for the aryl, 0.97 Å for the methylene, and 0.96 Å for the methyl H atoms with Uiso(H) = 1.2Ueq(C) for the aryl and methylene H atoms, and 1.5Ueq(C) for methyl H atoms.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as a small cycles of arbitrary radius.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq S 0.31784 (