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

The title compound, C18H16O3S, crystallizes with two symmetry-independent molecules in the asymmetric unit. The phenyl rings are rotated out of the benzofuran planes, making dihedral angles of 43.38 (7) and 56.13 (6)° in the two molecules. The carboxyl groups are involved in inversion-related 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 weak non-classical intermolecular C—H⋯O hydrogen bonds. The crystal structure also exhibits intermolecular C—H⋯π interactions, and two aromatic π–π interactions between the furan rings of neighbouring benzofuran systems; the centroid–centroid distances are 3.500 (3) and 3.605 (3) Å.

Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: NK2002).
The benzofuran unit is essentially planar, with a mean deviation of 0.006 (2) Å for A, and 0.024 (2) Å for B, respectively, from the least-squares plane defined by the nine constituent atoms. In the title compound, the dihedral angles formed by the phenyl ring and the plane of the benzofuran fragment are 43.38 (7) in A and 56.13 (6)° in B, respectively. In the crystal structure, the carboxylic acid groups are involved in inversion-related 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 non-classical intermolecular C-H···O hydrogen bonds (Table 1 and Fig. 2). The crystal structure (Fig. 3) is further stabilized by intermolecular C-H···π interactions between the phenyl H atom and the benzene ring of the adjacent molecule, with a C12-H12···Cg4 iv and a C30-H30···Cg2 v (Table 1; Cg2 and Cg4 are the centroids of the C2-C7 and the C20-C25 benzene rings, 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 80%, m.p. 413-414 K; R f = 0.79 (ethyl acetate)]. Single crystals suitable for X-ray diffraction were prepared by evaporation of a solution of the title compound in diisopropyl ether at room temperature.

Refinement
Atoms H2O and H5O of the hydroxy groups was found in a difference Fourier map and were refined with an O-H distance restraint of 0.82 (3) Å. 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, methylene and methyl H atoms.  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.