2-(Acetoxymethyl)benzoic acid

The title compound, C10H10O4, crystallizes with the well-known carboxylic acid dimer-forming R 2 2(8) hydrogen-bond motif. Chains approximately parallel to (-1-12) are then built through C(methylene,phenyl)–H⋯O(carbonyl) interactions [C(6) and C(8) motifs] with one (methyl)C—H⋯π interaction providing interplanar binding. The weakness of the latter interaction is consistent with the difficulty experienced in obtaining suitable single crystals.

The title compound, C 10 H 10 O 4 , crystallizes with the wellknown carboxylic acid dimer-forming R 2 2 (8) hydrogen-bond motif. Chains approximately parallel to (112) are then built through C(methylene,phenyl)-HÁ Á ÁO(carbonyl) interactions [C(6) and C(8) motifs] with one (methyl)C-HÁ Á Á interaction providing interplanar binding. The weakness of the latter interaction is consistent with the difficulty experienced in obtaining suitable single crystals.

2-(Acetoxymethyl)benzoic acid Graeme J. Gainsford and Ralf Schwörer Comment
The title compound was synthesized during our studies on substituted benzoyl protecting groups that could be selectively cleaved in the presence of other benzoate esters. We believe the structure has not been reported previously because of difficulties, which we experienced, in obtaining suitable non-twinned single crystals and the tendency of the title compound to cyclize with formation of phthalide. The compound crystallizes with one independent C 10 H 10 O 4 molecule in the asymmetric unit ( Fig. 1). Only two closely related structures with similar carboxylic acid hydrogen bonding links [R 2 2 (8) (Bernstein et al.,1995)] were found in the CSD (Allen, 2002): JOWTIY (Valentine et al., 1992) and UHELOI (Liu et al., 2002). The rather short intermolecular H2···O1 contact distance [1.667 (15) Å] (Table 1) is replicated in these two reports as 1.752 & 1.569 Å, respectively. A series of metal complexes containing the acetoxymethyl-moiety have been reported by Kan et al. (2012).
The crystal packing (Table 1) consists of the above-mentioned strong carboxylic acid hydrogen bonding in the plane of the molecule. This is coupled with C(methylene,phenyl)-H···O(carbonyl) interactions [C(6) & C(8) motifs] forming planar chains. One weak (methyl)C8-H10B···π interaction (labelled in Figure 2) crosslinks the planes of molecules, which are approximately parallel to the (-1,-1,2) crystal plane. This weak interplanar interaction is consistent with the difficulty in obtaining adequate non-twinned crystals.

Experimental
The synthesis of the title compound has been reported previously by Gorter-Laroij & Kooyman (1972). Crystals for analysis were obtained by dissolving the title compound in a minimal amount of ethyl acetate, followed by addition of petroleum ether 60-80.

Refinement
Eight outlier reflections, identified by large delta/sigma ratio (>4.8), were OMITted from the dataset (four were omitted on the basis of inconsistent equivalents). All methyl H atoms were constrained to an ideal geometry (C-H = 0.98 Å) with U iso (H) = 1.5U eq (C), but were allowed to rotate freely about the adjacent C-C bond. All other C bound H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with C-H distances of 1.00 (primary), 0.99 (methylene) or 0.95 (phenyl) Å and with U iso (H) = 1.2U eq (C). The hydroxyl hydrogen on O2 was refined with U iso (H) = 1.2U eq (O2)

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 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.