4,4′-[4,4′-Sulfonylbis(p-phenyleneoxy)]dibutanoic acid

In the title compound, C20H22O8S, the dihedral angle between the two benzene rings is 81.6 (3)°. The benzene-connected portions of the alkoxy substituents are almost coplanar with their respective rings [C—C—O—C torsion angles of 174.77 (17) and −178.5 (4)°]. One of the butanoic acid groups is disordered over two conformations with a site-occupancy ratio 0.719 (6):0.281 (6). In the crystal, pairs of O—H⋯O hydrogen bonds link the molecules into infinite zigzag chains along [130].

In the title compound, C 20 H 22 O 8 S, the dihedral angle between the two benzene rings is 81.6 (3) . The benzene-connected portions of the alkoxy substituents are almost coplanar with their respective rings [C-C-O-C torsion angles of 174.77 (17) and À178.5 (4) ]. One of the butanoic acid groups is disordered over two conformations with a site-occupancy ratio 0.719 (6):0.281 (6). In the crystal, pairs of O-HÁ Á ÁO hydrogen bonds link the molecules into infinite zigzag chains along [130]. Experimental Crystal Table 1 Hydrogen-bond geometry (Å , ).

Comment
Bisphenol S (BPS) is an organic compound with the formula (C 6 H 4 OH) 2 SO 2 . It has two phenol functional groups on either side of a sulfonyl group. It is commonly used as a reactant in epoxy reactions, and is used in fast-curing epoxy resin glues (Askarinejad & Morsali, 2006;Bashiri et al., 2009;Danzl et al., 2009;Yasue et al., 2009). Bisphenol S is also used in organic synthesis as an organosulfur source in the manufacture of pharmaceuticals, adhesives, biocides and agricultural products (Howard & David, 2002;Howard et al., 2005). In this article, we present the synthesis and crystal structure of a new potential ligand derived from bisphenol S, which contains multiple oxygen donors and flexible aliphatic spacers.
As shown in Figure 1, the benzene-connected portions of the alkoxy substituents lie almost coplanar with the ring [C-C-O-C torsion angle = 174.77 (17) and -178.5 (4)°, respectively]. The two benzene rings make a dihedral angle of 81.6 (3)°. It is noteworthy that one of the butanoic acid groups is disordered over two components with site occupancy ratio 0.719 (6):0.281 (6). In the crystal, O-H···O hydrogen bonds link the molecules into a zigzag 1-D infinite chain that propagates along the [1 3 0] direction. These chains are further interwoven by C-H···O and C-H···π contacts that stabilize the packing.

Experimental
Reagents and solvents were of commercially available quality. The title complex was synthesized according to the method of Zheng et al., 2007. To a solution of bisphenol S (0.01 mol) in acetonitrile (50 ml), anhydrous potassium carbonate (0.02 mol) and ethyl 4-bromobutanoate (0.01 mol) were mixed. The mixture solution was refluxed for 6 h and filtered. The filtrate was evaporated under reduced pressure and the solid product was dissolved in water/ethanol (1:2 v/v), then sodium hydroxide (0.02 mol) was added. The solution was refluxed for another 24 h, then acidified with dilute HCl. The crude product was separated by filtration and crystals of the title compound were prepared by recrystallization from a mixture of water and ethanol (1:1).

Refinement
All H atoms were placed in idealized positions (C-H = 0.93-0.97 Å, O-H = 0.82 Å and refined as riding atoms with U iso (H) = 1.2U eq (C) and with U iso (H) = 1.5U eq (O). One of the butanoic acid groups is disordered over two conformations with site occupancy ratio 0.719 (6):0.281 (6). All distances in the minor component were restrained to within 0.01 Å of their equivalents in the major component. Fig. 1. The molecular structure of the title compound, with displacement ellipsoids at the 30% probability level. The disorder in the minor component has been omitted to enhance clarity.

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 supplementary materials sup-3 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 > 2σ(F 2 ) is used only for calculating Rfactors(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.