N-(2-Chloroethyl)pyrazine-2-carboxamide

In the title molecule, C7H8ClN3O, the pyrazine and amide groups are almost co-planar [N—C—C—N torsion angle = −2.4 (2) °], a conformation stabilized by an intramolecular N—H⋯N hydrogen bond. The chloroethyl group lies out of the plane [N—C—C—Cl = −65.06 (17) °]. In the crystal, the presence of N—H⋯N hydrogen bonds leads to the formation of a C(6) supramolecular chain along the b axis. The carbonyl-O atom accepts two C—H⋯O interactions. These, plus Cl⋯Cl short contacts [3.3653 (6) Å], consolidate the packing of the chains in the crystal.

The use of the EPSRC X-ray crystallographic service at the University of Southampton, England, and the valuable assistance of the staff there is gratefully acknowledged. JLW acknowledges support from CAPES (Brazil).

Comment
Pyrazinamide has well known anti-mycobacterial activity and is the one of the most important drugs used in tuberculosis treatment (Chaisson et al., 2002;Gordin et al., 2000;de Souza, 2006). In continuation of our studies on pyrazinamide derivatives (Wardell et al., 2008;Baddeley et al., 2009;Howie et al., 2010aHowie et al., , 2010bHowie et al., , 2010cHowie et al., , 2010d, we report the structure of title compound, (I).
The pyrazine and amide groups are co-planar as seen in the value of the N1-C1-C2-N2 torsion angle of -2.4 (2) °, a conformation stabilized by an intramolecular N1-H···N2 hydrogen bond, Table 1. The ethyl group lies out of the plane through the rest of the molecule as seen in the N1-C6-C7-Cl1 torsion angle of -65.06 (17) °. The carbonyl-O1 lies to the opposite side of the molecule occupied by the amide and chlorido atoms.
In the crystal packing, the most prominent interactions are hydrogen bonding interactions of the type N-H···N, Table   1, which lead to a supramolecular chain along the screw axis, Fig. 2. The chains are connected into the 3-D structure by C-H···O interactions, involving the bifurcated carbonyl-O atom interacting with two methylene-H atoms, Table 1, and Fig. 3.

Experimental
The title compound was prepared by refluxing a mixture of thionyl chloride (1 ml) and N-(2-chloroethyl)pyrazine-2-carboxamide (0.2 g), obtained from methyl 2-pyrazinecarboxylate, ethanolamine and triethylamine. After 6 h, the excess thionyl chloride was removed under reduced pressure, the residue extracted into ethyl acetate (20 ml) and washed with saturated sodium bicarbonate solution (60 ml). The organic phase was dried over Na 2 SO 4 and concentrated under reduced pressure to afford title compound, yield: 70%; m. pt.: 384-386 K. The crystals used in the structure determination were grown from EtOH solution.

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.95-0.99 Å) and refined as riding with U iso (H) = 1.2U eq (C).
The N-bound H atom was located from a difference map and refined with the distance restraint N-H = 0.88±0.01 Å, and with U iso (H) = 1.2U eq (N).  Fig. 1. The molecular structure of (I) showing displacement ellipsoids at the 50% probability level.

Special details
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 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 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.