2-Acetylpyrazine 4-methylthiosemicarbazone

The title compound, C8H11N5S, has been prepared by the reaction of 2-acetylpyrazine with 4-methyl-3-thiosemicarbazide. It exists in the thione form and adopts the E configuration. The molecules are connected by the intermolecular N—H⋯N and N—H⋯S interactions.

This work was financially supported by the Foundation of the Education Department of Henan Province (No. 2007150012) Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: AT2513).

Comment
Thiosemicarbazone and its derivatives have attracted interest in recent years due to their beneficial biological applications (Padhye & Kauffman, 1985). The presence of alkyl groups at the terminal N(4) position can increase the biological activity (Liberta & West, 1992). So we report here the crystal structure of N(4)-methyl thiosemicarbazones derived from 2-acetylpyrazine.
The geometry of the title compound (I) is well planar (Fig. 1). The molecular exists in the E conformation about the C3-N3 bond as confirmed by the C5-C3-N3-N2 torsion angle of 179.6 °. The C-S bond distance of 1.679 (2) Å, which is much short than C-S single bond (Latheef et al., 2006), shows that the title compound adopts the thione form.
The bond length of C3-N3 is 1.283 (2) Å, which is within the range of typical bond length of C═N double bond. The bond length of N2-N3 is 1.368 (2) Å, accepted as typical for a single N-N bond, and in accordance with those of other thiosemicarbazone (Mendes et al., 2001;Hong et al., 2004).
In the crystal packing, the molecules are connected through an extended network of intermolecular hydrogen bonds involving the nitrogen atoms N1, N2, N4 and sulfur atom S1.

Experimental
All reagents were commercially available and of analytical grade. 2-Acetylpyrazine (0.24 g, 2 mmol) and 4-methyl-3-thiosemicarbazide (0.21 g, 2 mmol) were mixed in ethanol (30 ml). Eight drops of acetic acid were added and the solution was refluxed for 4 h. Crystals of (I) suitable for X-ray diffraction analysis were obtained from the filtrate by slow evaporation at room temperature.

Refinement
All H atoms were positioned geometrically and refined as riding with C-H = 0.96 Å (methyl) or 0.93 Å (aromatic), N-H = 0.86 Å and with U iso (H) = 1.2U eq (C, N) or 1.5U eq (C) for methyl groups. Fig. 1. The molecular structure of (I), showing atom displacement ellipsoids drawn 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 > 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.