2-(2-Furylmethylammonio)ethanesulfonate methanol solvate

The organic molecule of the title compound, C7H11NO4S·CH3OH, is a zwitterion and its furan ring displays positional disorder [occupancy 0.563 (5):0.437 (5)]. The crystal structure is extended into a three-dimensional supramolecular architecture through intermolecular O—H⋯O and N—H⋯O hydrogen bonds with participation of the methanol solvent molecules.

The organic molecule of the title compound, C 7 H 11 NO 4 SÁ-CH 3 OH, is a zwitterion and its furan ring displays positional disorder [occupancy 0.563 (5):0.437 (5)]. The crystal structure is extended into a three-dimensional supramolecular architecture through intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds with participation of the methanol solvent molecules.

Comment
In the previous literatures, a number of reduced or unreduced Schiff base complexes derived from taurine have been reported (Jiang et al., 2004(Jiang et al., , 2006Li et al., 2005Li et al., , 2006aLi et al., , 2007aLi et al., ,b, 2008aLiao et al., 2007;Zeng et al., 2003;Zhang et al., 2005), and they have shown novel chain (Li et al., 2007b), cubical (Li et al., 2008a and isomeric (Li et al., 2008b) structures except for the commonly seen mononuclear or binuclear compounds. Taurine, an amino acid containing sulfur, is indispensable to human beings and has important physiological functions. However, there have been sparse reports on the crystal structures of the corresponding free Schiff base ligands so far. In this paper, we report the crystal structure of a reduced Schiff base from taurine, (I) (Fig. 1).
The H atom of the sulfonic acid group is transferred to the amino N atom, forming the zwitterionic amino acid. This structure is completely similar to that of 2-(2-pyridylmethylammonio)ethanesulfonate dihydrate (Li et al., 2006b), where the H atom of the sulfonic acid group is also transferred to the amino N atom. The difference between them is that the furan ring here is positionally disordered. The two positions of furan ring have a dihedral angle of 180°. Other bond length and angles are in good agreement. Methanol molecules are involved in hydrogen bonds both as donors and acceptors, whereas ammonium acts only as a double donor (Table 1, Fig.2). Fig. 3 shows the crystal packing of (I), with hydrogen bonds as dashed lines in ac plane. The crystal of (I) is stabilized via these intermolecular hydrogen bonding interactions.

Experimental
Furan-2-carbaldehyde (0.96 g, 10 mmol) in MeOH (10 ml) was dropwise added to a solution of 2-aminoethanesulfonic acid (1.25 g, 10 mmol) in methanol (10 ml) containing KOH (0.56 g, 10 mmol). The yellow solution was stirred for about 2 h at room temperature prior to cooling in an ice bath. The intermediate Schiff base that formed was reduced with an excess of KBH 4 (0.79 g, 15 mmol). The yellow colour slowly discharged, and after 3 h the solution was adjusted with concentrated HCl to pH = 6.0. The resulting white solid was filtered off, washed with anhydrous methanol and diethyl ether. The obtained solid was dissolved in a ethanol-methanol mixture (1:1 v/v, 20 ml) and heated. When cooling, colourless granular-shaped crystals were obtained in a yield of 76%. Analysis, found: C 40.42, H 6.37, N 5.85, S 13.55%; C 8 H 15 NO 5 S requires: C 40.50,

Refinement
The H atoms bonded to C and N atoms were positioned geometrically with C-H distance of 0.93-0.97Å and N-H distances of 0.900 Å, and treated as riding atoms, with U iso (H) = 1.2 or 1.5U eq (C, N). The O-H hydrogen atom was located in a difference Fourier map and their positional and isotropic displacement parameters were refined; the applied restraint of the O-H distance wasere 0.820 Å, with U iso (H) = 1.5U eq (O).  Fig. 1. Molecular structure of (I), with displacement ellipsoids drawn at the 15% probability level.