3-Ethyl-4-hydroxy-8-methoxyquinolin-2(1H)-one

In the title compound, C12H13NO3, the quinoline ring system is approximately planar with a maximum deviation from the least-squares plane of 0.058 (2) Å. In the crystal, N—H⋯O and O—H⋯O hydrogen bonds link the molecules into chains running along the b-axis direction. The chains also feature π–π interactions between pyridine and benzene rings of inversion-related molecules [centroid–centroid distance = 3.609 (2) Å].

In the crystal structure of the title compound (I) (Fig. 2) two 3-ethyl-4-hydroxy-8-methoxyquinolin-2(1H)-one molecules are connected by two intermolecular N-H···O hydrogen bonds between protonated nitrogen atom and carbonyl group. These connections altogether with additional O-H···O hydrogen bonds between hydroxyl and carbonyl groups (Table 1) form linear chain along b axis. The chains are further stabilized by π-π interactions between pyridine and benzene rings of inversion-related pairs of quinoline molecules [centroid-centroid distance = 3.609 (2) Å].

Experimental
A mixture of o-anisidine (12.3 g, 100 mmol) and diethyl ethylmalonate (197.6 g, 105 mmol) was heated on a metal bath at 220-230 °C for 1 h and then at 260-270 °C for 6 h (until the distillation of ethanol stopped). The hot reaction mixture was cautiously poured into toluene (50 ml). After cooling, the precipitate was filtered. The residue was dissolved in aqueous sodium hydroxide solution (0.5 M, 300 ml) and the solution was filtered. The filtrate was washed with toluene (3 x 15 ml). The aqueous phase was filtered and acidified by addition of 10% hydrochloric acid to Congo red. The precipitated paste was triturated with a glass bar under an aqueous phase for several minutes and then the mixture was cooled in refrigerator for several hours, until the pasty substance hardened. The solid was filtered off, washed with water (100 ml), air dried and crystallized from ethanol affording 13.6 g (62% of theoretical yield) of the title compound (I), m. pt 496-498 K (benzene -ethanol). In the literature (Rapoport & Holden, 1959), a m. pt range of 498-499 K is reported.

Refinement
The N-bonded hydrogen atom was located in a difference map and refined with the using a distance restraint, N-H = 0.86±0.02 Å, and with U iso (H) = 1.2U eq (N). All other H atoms were included in the model at geometrically  (Spek, 2009) suggests that the structure could be twinned. However, applying the proposed twin law does not affect the refinement in the sense of better R values. Additionally, the BASF parameter has a value close to zero after refinement. Hence, a twin model was not employed.

Figure 1
A view of the title compound showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
The supramolecular chain in the crystal structure of (I), with the O-H···O and N-H···O hydrogen bonds, and π-π interactions denoted by dashed lines. Hydrogen atoms not involved in hydrogen bonding have been omitted for clarity.

Special details
Experimental. 279 frames in 4 sets of φ scans + ω scans. Rotation/frame = 1.6 °. Crystal-detector distance = 32 mm. Measuring time = 150 s/°. Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq N1 0.0025 (