(E)-N′-(4-Ethoxybenzylidene)-4-hydroxybenzohydrazide dihydrate

The benzohydrazide molecule of the title compound, C16H16N2O3·2H2O, exists in a trans conformation with respect to the C=N double bond. The central O=C—NH—N=C plane [r.m.s. deviation of 0.0165 (1) Å for the five non-H atoms] makes dihedral angles of 6.04 (8) and 2.38 (8)°, respectively, with the hydroxy- and ethoxy-substituted benzene rings. The dihedral angle between these benzene rings is 3.82 (7)°. The ethoxy group is almost coplanar with the attached benzene ring with a C—O—C—C torsion angle of −176.58 (11)°. In the crystal, the benzohydrazide and water molecules are linked by N—H⋯O, O—H⋯O , O—H⋯N and C—H⋯O hydrogen bonds into a three-dimensional network.

Data collection: APEX2 (Bruker, 2005); cell refinement: SAINT (Bruker, 2005); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009 It has been known that a majority of benzohydrazides possesses various biological properties, such as antibacterial and antifungal (Loncle et al., 2004), and antiproliferative (Raj et al., 2007) activities. The title benzohydrazide derivative (I) was synthesized as part of our study on the bioactivity of benzohydrazide derivatives Horkaew et al., 2011Horkaew et al., , 2012Promdet et al., 2011) and was evaluated for antioxidant activity by DPPH scavenging (Molyneux, 2004). It was found to be active. Herein we report the synthesis and crystal structure of (I).
The title compound ( (Allen et al., 1987) and are comparable with the related structures Horkaew et al., 2011Horkaew et al., , 2012.
In the crystal packing ( Fig. 2), the molecules of benzohydrazide and water are linked by N-H···O, O-H···O, O-H···N and C-H···O hydrogen bonds (Table 1) into a three-dimensional network.

Experimental
The title compound (I) was prepared by dissolving 4-hydroxybenzohydrazide (2 mmol, 0.30 g) in ethanol (15 ml). A solution of 4-ethoxybenzaldehyde (2 mmol, 0.27 ml) in ethanol (15 ml) was then added slowly to the reaction. The mixture was refluxed for around 6 hr. The solution was then cooled to room temperature and a white solid appeared.
Colorless block-shaped single crystals of the title compound suitable for X-ray structure determination were recrystallized from a methanol solution by slow evaporation of the solvent at room temperature after several days (m.p. 373-374 K).

Refinement
All H atoms were positioned geometrically [d(O-H) = 0.84 Å for the hydroxy group and 0.81-0.89 Å for water molecules, d(N-H) = 0.85 Å, d(C-H) = 0.95 Å for aromatic and CH, 0.99 Å for CH 2 and 0.98 Å for CH 3 groups] and allowed to ride on their parent atoms, The U iso (H) values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl group.

Figure 1
The molecular structure of the title compound, showing 60% probability displacement ellipsoids and the atom-numbering scheme. The O-H···O hydrogen bond is shown as a dashed line.

Figure 2
The crystal packing of the title compound viewed along the a axis. Hydrogen bonds are shown as dashed lines.  (Cosier & Glazer, 1986) operating at 120.0 (1) K. Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.