Ethyl 2-[(3-chlorophenyl)hydrazono]-3-oxobutanoate

The molecule of the title oxobutanoate derivative, C12H13ClN2O3, adopts a keto–hydrazo tautomeric form and is roughly planar, the angle between the benzene ring and the mean plane through the hydrazone and aliphatic chain being 1.49 (6)°. This planarity is further aided by the formation of an intramolecular N—H⋯O hydrogen bond which generates an S(6) ring motif. The aromatic ring and aliphatic chain have a trans configuration with respect to the N—N bond. In the crystal packing, centrosymmetric R 2 2(16) dimers are formed through pairs of weak C—H⋯O(3-oxo) interactions. These dimers are linked together through weak C—H⋯O(carboxylate C=O) interactions into ribbons along the b-axis direction. These ribbons are stacked along the a-axis direction. The crystal also exhibits Cl⋯Cl [3.4988 (6) Å] and C⋯O [3.167 (2)–3.335 (2) Å] short contacts.

The molecule of the title oxobutanoate derivative, C 12 H 13 ClN 2 O 3 , adopts a keto-hydrazo tautomeric form and is roughly planar, the angle between the benzene ring and the mean plane through the hydrazone and aliphatic chain being 1.49 (6) . This planarity is further aided by the formation of an intramolecular N-HÁ Á ÁO hydrogen bond which generates an S(6) ring motif. The aromatic ring and aliphatic chain have a trans configuration with respect to the N-N bond. In the crystal packing, centrosymmetric R 2 2 (16) dimers are formed through pairs of weak C-HÁ Á ÁO(3-oxo) interactions. These dimers are linked together through weak C-HÁ Á ÁO(carboxylrboxylate C O) interactions into ribbons along the b-axis direction. These ribbons are stacked along the a-axis direction. The crystal also exhibits ClÁ Á ÁCl [3.4988 (6) Å ] and CÁ Á ÁO [3.167 (2)-3.335 (2) Å ] short contacts.

Comment
In recent years, the chemistry of hydrazones have been the subject of intense study mostly due to their biological significance.

Experimental
The title compound was prepared by disolving 3-chloroaniline (1.27 g, 10 mmol) in dilute hydrochloric acid (11.0 ml), obtained by mixing 4.5 ml of 12 M HCl and 6.5 ml water. The solution was cooled to 273 K in ice bath. To this, a cold solution of sodium nitrite (1.6 g, 23.1 mmol in 5.0 ml water) was added. The temperature of reaction mixture was not allowed to rise above 323 K. The diazonium salt solution so formed was poured through a filter into a cooled solution of ethylacetoacetate (1.7 ml) and sodium acetate (3.5 g) in ethanol (50 ml). The resulting yellow solid was filtered, washed with ice cold water, dried in air and recrystallized from methanol. Yield was found to be 1.70 g (70 %), M.p. 360 K.

Refinement
The hydrazone H atom was located in a difference map and refined isotropically. The remaining H atoms were placed in calculated positions with d(C-H) = 0.93 Å for aromatic, 0.97 for CH 2 and 0.96 Å for CH 3 atoms. The U iso values were sup-2 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 groups. The highest residual electron density peak is located at 0.86 Å from Cl1 and the deepest hole is located at 1.19 Å from C2. The difference electron density map also indicated possible tautomerism with the docking site (N2). However, the 1 H NMR experiments did not confirm this tautomerism. Moreover it would be difficult to model a resonance structure that would be in agreement with the presumed tautomerism.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 120.0 (1) K. 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 > σ(F 2 ) is used only for calculating Rfactors(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 Cl1 1.05405 (13