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

There are two molecules in the asymmetric unit of the title compound, C14H16O3S. 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 a axis by aromatic π–π interactions between the furan rings of adjacent molecules [centroid–centroid distance = 3.430 (4) Å] and by additional C—H⋯π and C—H⋯O interactions.

There are two molecules in the asymmetric unit of the title compound, C 14 H 16 O 3 S. 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 a axis by aromaticinteractions between the furan rings of adjacent molecules [centroid-centroid distance = 3.430 (4) Å ] and by additional C-HÁ Á Á and C-HÁ Á ÁO interactions.
The benzofuran unit is essentially planar, with a mean deviation of 0.003 (2) Å for A and 0.011 (2) Å for B, respectively, 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 ( Fig. 2 and Table 1), which link the molecules into centrosymmetric dimers.
These dimers are further packed into stacks along the a-axis by aromatic π-π interactions between the furan rings from the adjacent molecules. The Cg1···Cg3 distance is 3.430 (4) Å (Cg1 and Cg3 are the centroids of C1/C2/C7/O1/C8 furan ring and C15/C16/C21/O4/C22 furan ring, respectively). In addition, the crystal packing exhibits two different C-H···π interactions between a methylene H atom and the benzene ring from adjacent molecules (Table 1 and Fig. 2); Cg2 and Cg4 are the centroids of the C2-C7 benzene ring and the C16-C21 benzene ring, respectively, and a non-classical C-H···O hydrogen bond between a benzene H atom and the O atom of the hydroxy group (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 (hexane-ethyl acetate,1 : 2 v/v) to afford the title compound as a colorless solid [yield 85%, m.p. 412-413 K; R f = 0.69 (hexane-ethyl acetate, 1 : 2 v/v )]. Single crystals suitable for X-ray diffraction were prepared by evaporation of a solution of the title compound in benzene at room temperature.

Refinement
Atoms H2O and H5O of the hydroxy groups were 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 = 0.95 Å for the aryl, 0.99 Å for the methylene, 1.00 Å for the methine, and 0.98 Å for the methyl H atoms.Uiso(H) = 1.2Ueq(C) for the aryl, methine and methylene H atoms, and 1.5Ueq(C) for 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.