5-(Methoxycarbonyl)thiophene-2-carboxylic acid

In the title compound, C7H6O4S, a monoester derivative of 2,5-thiophenedicarboxylic acid, the carboxylic acid and the carboxylic acid ester groups are approximately coplanar with thiophene ring, making a dihedral angle of 3.1 (4) and 3.6 (4)°, respectively. In the crystal structure, molecules are connected by classical intermolecular O—H⋯O hydrogen bonds, forming centrosymmetric dimers.

In the title compound, C 7 H 6 O 4 S, a monoester derivative of 2,5-thiophenedicarboxylic acid, the carboxylic acid and the carboxylic acid ester groups are approximately coplanar with thiophene ring, making a dihedral angle of 3.1 (4) and 3.6 (4) , respectively. In the crystal structure, molecules are connected by classical intermolecular O-HÁ Á ÁO hydrogen bonds, forming centrosymmetric dimers.

Comment
The derivates of thiophene have been viewed as significant compounds for application in many fields, such as photo-material, electronic luminescence material (Zhao et al., (2009)). Many simple structures containing thiophene ring were synthesized for their derivates. When substituted with different active function groups, a series of valuable derivates of thiophene can be obtained. It may be used as a source to synthesize compounds which has more complex structures. The title compound was synthesized as a promising compound with biological activities and a precursor for the synthesis of various functional compounds for its delocalized structure.
In the structure of the title compound ( Fig. 1), the carboxylate groups are approximately coplanar with thiophene ring. The co-plane connection makes the π-conjugation expanded in a larger range. In the crystal structure, molecules are connected by intermolecular O4-H4···O3 i hydrogen-bonding interactions (Table 1) forming a dimer (Fig. 2). Symmetry code: (i) -x, -y+1, -z+1.

Experimental
Sodium (230 mg, 10 mmol) was dissolved in 40 ml of absolute methanol, the resulting solution was adopted into a solution of dimethylthiophen-2,5-dicarboxylate (2000 mg, 10 mmol) in 60 ml of absolute methanol. The resulting mixture was heated at 343 K for 5 h, cooled, and the filtrated. The filtrate was acidified with HCl (6 mol.L -1 ) to pH about 5. As the HCl being adopted, the product was formed as colourless solid (yield: 152 mg, 82%). Recrystallized with methanol at room temperature afforded colourless crystal. IR-spectrum (KBr): v = 3097, 1728, 1712 cm -1 .

Refinement
All H atoms were geometrically fixed and allowed to ride on their attached atoms, which C-H = 0.93-0.96Å and U iso (H) = 1.2-1.5U eq (C) and O-H = 0.82Å and U iso (H) = 1.2U eq (O). Fig. 1. Molecular structure of title compound with the atom numbering scheme. Displacement ellipsoids are drawn at 30% probability level. H atoms are presented as a small spheres of arbitrary radius.

Special details
Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The 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 > σ(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 )