3-Acetoxy-2-naphthoic acid

In the title compound, C13H10O4, an analog of acetylsalicylic acid, the naphthalene unit is twisted slightly due to ortho disubstitution [dihedral angle between conjugated rings system in the naphthalene unit = 2.0 (2)°]. The mean planes of the carboxylic and ester groups are almost coplanar and perpendicular, respectively, to the mean plane of the conjugated aromatic system, making dihedral angles of 8.9 (3) and 89.3 (1)°. In the crystal, molecules are paired through their carboxylic groups by the typical centrosymmetric O—H⋯O interactions with R 2 2(8) hydrogen-bond motifs. In addition, several weak C—H⋯O intermolecular contacts are also observed. Finally, the molecules are stacked along crystallographic [100] and [010] directions.

In the title compound, C 13 H 10 O 4 , an analog of acetylsalicylic acid, the naphthalene unit is twisted slightly due to ortho disubstitution [dihedral angle between conjugated rings system in the naphthalene unit = 2.0 (2) ]. The mean planes of the carboxylic and ester groups are almost coplanar and perpendicular, respectively, to the mean plane of the conjugated aromatic system, making dihedral angles of 8.9 (3) and 89.3 (1) . In the crystal, molecules are paired through their carboxylic groups by the typical centrosymmetric O-HÁ Á ÁO interactions with R 2 2 (8) hydrogen-bond motifs. In addition, several weak C-HÁ Á ÁO intermolecular contacts are also observed. Finally, the molecules are stacked along crystallographic [100] and [010] directions.

Comment
Besides electronic effects, intramolecular reactions depend on the spatial relationship of the reacting groups (Orth et al., 2010). Subtle changes in the structure of similar compounds may lead to different relationships between nucleophilic-electrophilic centers within similar molecules, leading to different reaction mechanisms in solution. On this basis, we are currently studying the hydrolysis of a series of structurally related naphthyl esters. In a previous report (Souza et al., 2007), we published the structure of 2-carboxy-1-naphthyl acetate, a naphthoic acid bearing an ortho-ester group. In that structure, the dihedral angle between the aromatic mean plane and the ester group is 80.34 (5)°, considerably smaller than the one observed in α-naphthyl acetate (86.50°) (Gu et al., 2001), and we explained this difference in terms of an attractive interaction between the ester and the acid groups in 2-carboxy-1-naphthyl acetate. In the current work, we report the structure of 3-acetoxy-2-naphthoic acid I ( Fig. 1), C 13 H 10 O 4 , an acetylsalicylic analog. In this system the dihedral angle between acetoxy and aromatic mean planes is 89.3 (1)°, while the carboxylic acid group and naphthalene ring are almost coplanar with dihedral angle of 8.9 (3)°. Packing is controlled by carboxylic acid dimer formation, involving centrosymmetric O2-H···O1 interactions (R 2 2 (8) hydrogen bond pattern, Fig. 2). Several weak C-H···O intermolecular contacts are also observed. Finally, the molecules are stacked along crystallographic [100] and [010] directions (Fig. 3).

Experimental
The title compound was prepared by following the procedure reported by Bergeron et al., (1996). Concentrated sulfuric acid (10 drops) was added to a refluxing mixture of 3-hydroxy-2-naphthoic acid (3.50 g, 18.6 mmol) in acetic anhydride (8 ml, 89.7 mmol). The mixture was kept under reflux for 10 additional minutes and, after cooling to room temperature, the pale solid was filtered off and recrystallized in aqueous ethanol. The 10 mg of the prepared 3-acetoxy-2-naphthoic acid were dissolved in 5 ml of dry CHCl 3 in a 10 ml glass vial and the flask was kept in a saturated petroleum ether (313-333 K) atmosphere at 293 K, giving the title compound as pale yellow crystals that melt at 458-459 K.

Refinement
All non-H atoms were refined with anisotropic displacement parameters. H atoms were placed at their idealized positions with distances of 0.93Å for C-H Ar and 0.96Å for CH 3 group. Their U iso H were fixed at 1.2 and 1.5 times U eq C of the preceding atom for aromatic and methyl group, respectively. The hydrogen atom of the acid group was located from the Fourier difference map and treated using a riding model with U iso H = 1.2U eq O.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound with the atom labeling scheme. Displacement ellipsoids are shown at the 40% probability level. H atoms are presented as a small spheres of arbitrary radius.