2-[2-Hydroxy-4-(pyrrolidin-1-yl)benzoyl]benzoic acid

The title compound, C18H17NO4, crystallizes with two independent molecules in the asymmetric unit. The pyrrolidine ring in one molecule is disordered over two positions, with refined site-occupancy factors of 0.853 (5) and 0.147 (5). The dihedral angles between the planes of the benzene rings in the two independent molecules are 56.8 (2) and 68.2 (5)°. The molecular conformations are stabilized by intramolecular O—H⋯O hydrogen bonds. In the crystal structure, molecules are linked by intermolecular O—H⋯O hydrogen bonds, forming dimers and generating rings of graph-set motif R 2 2(8).


Experimental
Data collection: CrystalClear (Rigaku, 2005); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.  et al., 2005) and its derivatives (Masakichi et al., 1974). It has been synthesized from 3-pyrrolidinylphenol and phthalic anhydride in toluene (Luo et al.,1994). Although its synthesis has been studied, the crystal structure of title compound has not been investigated. In this paper we reported its crystal structure.
The title compound crystallizes with two independent molecules in the asymmetric unit (Fig. 1). Bond lengths and angles within the pyrrolidine rings are normal and in good agreement with those reported previously for 2,4,6-tripyrrolidino-2',4',6'trinitrobiphenyl (Effenberger et al., 1983). The dihedral angles between the planes of the benzene rings in the two independent molecules are 56.8 (2) and 68.2 (5)°. The molecular conformations are stabilized by intramolecular O-H···O hydrogen bonds (Table 1). In the crystal packing, the molecules are linked by intermolecular O-H···O hydrogen bonds to form dimers generating rings of graph-set motif R 2 2 (8) (Bernstein et al., 1995).

Experimental
A solution of 3-pyrrolidinylphenol (1.20 g, 7.36 mmol) and phthalic anhydride (1.31 g, 8.83 mmol) in toluene was refluxed under N 2 for 3 h. The mixture was cooled to 50-60°C. Then 7 ml of 35.0% aqueous NaOH (w/w) was added and heated at 90° C for 6 h. The resulting mixture was poured into 70 ml of H2O, acidified with hydrochloric acid, and allowed to stand at room temperature for 2 h. The suspension was then filtered. The solid was recrystallized from a mixture of water and methanol, and then dried to afford the desired product (1.63 g, 70.7%). Crystals suitable for X-ray diffraction were obtained by slow evaporation of a CD 3 OD/CDCl 3 (5:1 v/v) solution.

Refinement
Hydroxy H atoms were found on a difference Fourier map and isotropically refined with U iso (H) = 1.5 U eq (O). All other H atoms were placed at calculated positions and refined using a riding model, with C-H = 0.95-0.99 Å and with U iso (H) = 1.2U eq (C). The pyrrolidine group in one molecular was found to be disordered. Atoms C19, C20 and C21 were therefore refined over two positions with refined occupancies of 0.853 (5) and 0.147 (5) for primed and unprimed atoms, respectively. Fig. 1

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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.