2-[(4-Chlorobenzyl)carbonylmethyl]benzoic acid

The title compound, C16H13ClO3, is an important intermediate in the conversion of isocoumarin to 3,4-dihydroisocoumarin. The two aromatic rings are oriented at a dihedral angle of 67.18 (3)°. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the molecules into centrosymmetric dimers. There is also a C—H⋯π contact between the benzoic acid and 4-chlorobenzyl rings.

The title compound, C 16 H 13 ClO 3 , is an important intermediate in the conversion of isocoumarin to 3,4-dihydroisocoumarin. The two aromatic rings are oriented at a dihedral angle of 67.18 (3) . In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds link the molecules into centrosymmetric dimers. There is also a C-HÁ Á Á contact between the benzoic acid and 4-chlorobenzyl rings.

Comment
The isocoumarin nucleus is an abundant structural motif in natural products (Barry, 1964). Many constituents of the steadily growing class of known isocoumarins exhibit valuable biological properties such as antifungal (Sturtz et al., 2002), antitumor or cytotoxic, anti-inflammatory, anti-allergic (Rossi et al., 2003 and enzyme inhibitory activity (Powers et al., 2002).
Naturally occurring haloisocoumarins and their halogeno-3,4-dihydroisocoumarin derivatives are very rare. However, a few examples of naturally occurring chlorine containing isocoumarins are known (Thomas & Jens, 1999). In view of the importance of this class of compounds, the title compound, an intermediate during the conversion of isocoumarin to 3,4-dihydroisocoumarin, has been synthesized, and we report herein its crystal structure.
In the crystal structure, intermolecular O-H···O hydrogen bonds (Table 1) link the molecules into centrosymmetric dimers ( Fig. 2), in which they may be effective in the stabilization of the structure. There also exist a C-H···π contact (Table 1) between the benzoic acid and 4-chlorobenzyl rings.

Experimental
A solution of 3-(4-chlorobenzyl)isocoumarin (2.0 g, 7 mmol) in ethanol (50 ml) and potassium hydroxide (100 ml, 5%) were refluxed for 4 h. Ethanol was removed from the reaction mixture by distillation. Ice cold water (20 ml) was added and the reaction mixture was acidified with hydrochloric acid. It was extracted with dichloromethane (3 × 20 ml), and then dried and evaporated to yield the crude solid, which was recrystallized from methanol (yield; 85%; m.p. 414-415 K).

Refinement
H atoms were positioned geometrically, with O-H = 0.82 Å (for OH) and C-H = 0.93 and 0.97 Å for aromatic and methylene H, respectively, and constrained to ride on their parent atoms with U iso (H) = 1.2U eq (C,O). Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme.