2-(3-Ethylsulfanyl-5-fluoro-1-benzofuran-2-yl)acetic acid

The title compound, C12H11FO3S, was prepared by alkaline hydrolysis of ethyl 2–(3–ethylsulfanyl–5–fluoro–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 aromatic π–π interactions between the furan ring and the benzene ring of neighbouring benzofuran ring systems [centroid–centroid distance = 3.684 (5) Å].

Here we report the crystal structure of the title compound (Fig. 1).
The benzofuran unit is essentially planar, with a mean deviation of 0.005 (2) 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 aromatic π···π interactions between the furan ring and the benzene ring of adjacent benzofuran ring systems. The Cg1···Cg2 ii distance is 3.684 (5) Å ( Fig. 2; Cg1 and Cg2 is the centroids of the C1/C2/C7/O1/C8 furan ring and the C2-C7 benzene ring, respectively).
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 87%, m.p. 401-402 K; R f = 0.69 (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. Spectroscopic analysis: EI-MS 254 [M + ].

Refinement
Atom H2 of the hydroxy group was found 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 U iso (H) = 1.2U eq (C) for the aryl and methylene H atoms, and 1.5U eq (C) for the 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 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.