(1E,2E)-1,2-Bis(2,3,4-trimethoxybenzylidene)hydrazine

The title compound, C20H24N2O6, was obtained as an unexpected product by the reaction of hydrazinium dithiocarbazate with 2,3,4-trimethoxybenzaldehyde in refluxing ethanol. The molecule lies on a center of inversion. The crystal packing is stabilized by weak intermolecular C—H⋯O interactions.


Related literature
The surprising formation of the title hydrazone was probably due to the decomposition of hydrazinium dithiocarbazate in solution resulting in the formation of hydrazine, which then reacted with 2,3,4-trimethoxybenzaldehdye. Hydrazinium dithiocarbazates are known to decompose on heating (Rudorf, 2007). For the biological activity of Schiff bases, see: Akbar Ali et al. (2008); Chan et al. (2008). For a previous report of the title compound (the X-ray structure was not provided), see: Praefcke et al. (1991). For comparison bond lengths in an aroyl hydrazone, see: Ji et al. (2010).

Comment
The compound, C 20 H 24 N 2 O 6 (I) was obtained by the reaction of hydrazinium dithiocarbazate and 2,3,4-trimethoxybenzaldehyde in boiling ethanol. The surprising formation of the hydrazone was probably due to the decomposition of hydrazinium dithiocarbazate in solution resulting in the formation of hydrazine, which then reacted with 2,3,4-trimethoxybenzaldehdye to form the corresponding hydrazone (I). Hydrazinium dithiocarbazates are known to decompose on heating (Rudorf, 2007).
Schiff bases have attracted considerable attention because they can act as chelating agents for metal ions and many of them also exhibit useful biological activities (Akbar Ali et al., 2008;Chan et al., 2008). Although the compound has previously been reported its X-ray structure has not been provided (Praefcke et al., 1991). Hydrazones derived from the reactions of hydrazines with aldehydes or ketones are common but bis-hydrazones are not.
The molecular structure of (I) is shown in Figure 1 and its selected bond lengths and angles are given in Table 1 (Ji et al. 2010) shows that the bond is shorter than a single N-N bond (1.44 Å) indicating that a significant π-charge delocalization occurs along the C-N-N-C moiety. As the bond angles C6-C10-N1 (121.68°) and C6A-C10A-N1A (121.68°) are close to that of a sp 2 -hybridized carbon atom (ca 120°), the molecule does not have a distorted geometry. Due the fact that the molecule lies on a center of inversion the dihedral angle between the two phenyl rings is 0.0°. Figure 2 shows the packing of (I) in the unit cell. The packing diagram shows that there are intermolecular hydrogen bonds between one of the CH3 hydrogen atoms of one molecule with an ether oxygen of another molecule.

Refinement
H atoms were placed in geometrically idealized positions and constrained to ride on their parent atoms with a C-H distances of 0.95 Å and 0.98 Å, U iso (H) = 1.2U eq (C). Fig. 1. The title compound, C 20 H 24 N 2 O 6 with atom labeling. Displacement ellipsoids are at the 50 % probability level.  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.