3-Ethyl-3-hydroxy-8-methoxyquinoline-2,4(1H,3H)-dione monohydrate

In the title hydrate, C12H13NO4·H2O, the piperidine ring that is fused to the benzene ring is in a sofa conformation with the chiral C atom lying 0.4084 (18) Å out of the plane of the nine fused-ring atoms. In the crystal, O—H⋯O and N—H⋯O hydrogen bonds link the organic molecules and water molecules into chains running along the b-axis direction. The chains are further connected into layers parallel to the bc plane by π–π interactions between inversion-related benzene rings [centroid–centroid distance = 3.8846 (9) Å].

In the title hydrate, C 12 H 13 NO 4 ÁH 2 O, the piperidine ring that is fused to the benzene ring is in a sofa conformation with the chiral C atom lying 0.4084 (18) Å out of the plane of the nine fused-ring atoms. In the crystal, O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds link the organic molecules and water molecules into chains running along the b-axis direction. The chains are further connected into layers parallel to the bc plane byinteractions between inversion-related benzene rings [centroid-centroid distance = 3.8846 (9) Å ].
The asymmetric unit of the title compound (I) consists of a single 3-ethyl-3-hydroxy-8-methoxyquinoline-2,4(1H,3H)dione molecule and solvated water molecule (Fig. 1). The piperidine ring that is fused to the benzene ring has a sofa shape with chiral carbon center 0.4084 (18) Å out of the plane for 9 ring atoms. In the crystal packing organic molecules and solvated water molecules are connected by two intermolecular O-H···O and one N-H···O hydrogen bonds. These connections altogether with additional O-H···O hydrogen bonding between hydroxyl and carbonyl groups (Table 1) form linear chain running along the b axis. Non-covalent π-π interactions occur between inversion-related benzene rings [centroid-centroid distance = 3.8846 (9) Å], which stabilize the crystal packing and connect the chains into a twodimensional supramolecular layer parallel to the bc plane (Fig. 2).

Experimental
To a solution of 3-ethyl-4-hydroxy-8-methoxyquinolin-2(1H)-one (4.38 g, 20.0 mmol) in 0.5 M sodium hydroxide (120 ml), 30% peroxyacetic acid in acetic acid (6.7 ml, 30 mmol) was added drop-wise within 30 min under stirring at room temperature. After several minutes a precipitate started to form. The reaction mixture was stirred for additional 30 min and then left at 10 °C overnight. The solid phase was filtered off under suction, dispersed in 5% aqueous sodium bicarbonate solution (25 ml), filtered off and washed with water (3 x 20 ml). Crystallization of the above air-dried solid from toluene afforded 3.92 g (83%) of the final product (I), M.pt 371-372 K.

Refinement
The N-bonded hydrogen atom was located in a difference map and refined with the using distance restraint with N-H = 0.86±0.02 Å and with U iso (H) = 1.2U eq (N). Water H atoms were located in a difference map and refined with U iso (H) =

Special details
Experimental. 211 frames in 4 sets of φ scans + ω scans. Rotation/frame = 2 °. Crystal-detector distance = 31 mm. Measuring time = 20 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 O1 0.08014 (