2-(5-Fluoro-7-methyl-3-methylsulfanyl-1-benzofuran-2-yl)acetic acid

The title compound, C12H11FO3S, was prepared by alkaline hydrolysis of ethyl 2-(5-fluoro-7-methyl-3-methylsulfanyl-1-benzofuran-2-yl)acetate. In the crystal, the carboxyl groups are involved in intermolecular O—H⋯O hydrogen bonds, which link the molecules into centrosymmetric dimers.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: XU5266). Galal et al., 2009, Khan et al., 2005. These benzofuran derivatives occur in a wide range of natural products (Akgul & Anil, 2003;Soekamto et al., 2003). As a part of our ongoing study of the substituent effect on the solid state structures of 2-(5-halo-3-methylsulfanyl-1-benzofuran-2-yl) acetic acid analogues (Choi et al., 2009a,b), we report herein the crystal structure of the title compound In the title molecule ( Fig. 1), 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. The carboxyl groups are involved in intermolecular O-H···O hydrogen bonds (Table 1), which link the molecules into centrosymmetric dimers.

Experimental
Ethyl 2-(5-fluoro-7-methyl-3-methylsulfanyl-1-benzofuran-2-yl)acetate (338 mg, 1.2 mmol) was added to a solution of potassium hydroxide (337 mg, 6 mmol) in water (10 ml) and methanol (10 ml), and the mixture was refluxed for 5 h, then cooled. 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 at reduced pressure. The residue was purified by column chromatography (ethyl acetate) to afford the title compound as a colorless solid [yield 82%, m.p. 436-437 K; R f = 0.65 (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
All H atoms were positioned geometrically and refined using a riding model, with O-H = 0.84 Å, and C-H = 0.95 Å for aryl, 0.99 Å for methylene and 0.98 Å for methyl H atoms, respectively. U iso (H) = 1.5U eq (O), and 1.2U eq (C) for aryl and methylene, and 1.5U eq (C) for 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 supplementary materials sup-3 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.