5-Methyl-3-phenylisoxazole-4-carboxylic acid

In the title compound, C11H9NO3, the phenyl and isoxazole rings form a dihedral angle of 56.64 (8)°. The carboxy group is almost in the same plane as the isoxazole ring with a C—C—C—O torsion angle of −3.3 (2)°. In the crystal, pairs of O—H⋯O hydrogen bonds link the molecules into head-to-head dimers. C—H⋯N hydrogen bonds and π–π stacking interactions between phenyl rings [centroid–centroid distance = 3.9614 (17)Å] link the dimers into a three-dimensional network.

In the title compound, C 11 H 9 NO 3 , the phenyl and isoxazole rings form a dihedral angle of 56.64 (8) . The carboxy group is almost in the same plane as the isoxazole ring with a C-C-C-O torsion angle of À3.3 (2) . In the crystal, pairs of O-HÁ Á ÁO hydrogen bonds link the molecules into head-to-head dimers. C-HÁ Á ÁN hydrogen bonds andstacking interactions between phenyl rings [centroid-centroid distance = 3.9614 (17)Å ] link the dimers into a three-dimensional network.
As part of our interest in these compounds and our extensive background on isoxazole derivatives, we have synthesized the title compound to study its crystal structure.  (19)°. The carboxylic acid group at C12 is almost in the same plane as the isoxazole ring (C7-C12-C13-O15 torsion angle = -3.3 (2)°). The bond lengths and angles are within normal ranges and are comparable to related structure (Wolf et al., 1995& Chandra et al., 2013. The crystal structure is stabilized by O-H···O bonds (Table 1), which define head to head dimers, and weaker C-H···N bonds (Table 1), thus defining planes parallel to (101) (Fig 2). Finally, there are π···π stacking interacions between phenyl rings with Cg···Cg[1-x,1-y,-z] and slippage displacement distances of 3.9614 (17)Å and 1.284Å respectively (Fig 3) which link planes into a 3D structure.

Experimental
A mixture of benzaldehyde oxime (1 mmol), ethyl acetoacetate (2 mmol) and anhydrous zinc chloride (0.1 mmol) were taken in a 10 ml round bottomed flask and the contents were gradually heated to 60°C without any solvent for about one hour. After completion of the reaction (as indicated by TLC), the mixture was cooled to room temperature and ethanol was added with stirring for about 30 min. The solid ethyl 5-methyl-3-phenylisoxazole-4-carboxylate thus obtained was treated with 5% NaOH (10 ml) at room temperature for about 4hr. After completion of the reaction (as indicated by TLC), the reaction mixture was acidified with 2 N HCl. The solids thus obtained were filtered and recrystalized from hot ethanol to get crystals of the title compound.

Refinement
H atoms were placed at idealized positions and allowed to ride on their parent atoms with C-H distances in the range of 0.93 to 0.96 Å; U iso (H) = 1.2U eq (carrier atom) for all H atoms.

5-Methyl-3-phenylisoxazole-4-carboxylic acid
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.19 e Å −3 Δρ min = −0.14 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), FC * =KFC[1+0.001XFC 2 Λ 3 /SIN(2Θ)] -1/4 Extinction coefficient: 0.078 (6) Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > σ(F 2 ) is used only for calculating -R-factor-obs 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.