Crystal structure of C-2-benzothiazole-N-methylnitrone

The molecule of the title compound {systematic name: N-[(benzothiazol-2-yl)methylidene]methylamine N-oxide}, C9H8N2OS, is close to planar [maximum deviation from the mean plane = 0.081 (2) Å], its conformation being stabilized by a strong intramolecular attractive S⋯O interaction [2.6977 (16) Å]. In the crystal, molecules are linked into centrosymmetric dimers by pairs of weak C—H⋯O hydrogen bonds.


S1. Chemical context
One of the most important approaches for the symthesis of various five-membered heterocyclic systems is the 1,3-dipolar cycloaddition reaction. The use as dipoles of compounds such as nitrile oxides and nitrones leads to a wide range of N,Ocontaining heterocyclic systems (isoxazole, isoxazoline, isoxazolidine; Tufariello, 1984), which have biological activity and can be used as starting materials for the synthesis of acyclic compounds (for example, 1,3-aminoalcohols by cleavage of the N-O bond ;Torssell, 1988). On the other hand, compounds containing the benzothiazole moiety are of biological and industrial interest. In fact, benzothiazole derivatives possess a wide spectrum of biological applications such as antitumor (Bradshaw et al., 2002), anti-inflammatory (Paramashivappa et al., 2003), anticonvulsant (Jimonet et al., 1999), and antimicrobial activities (Ul-Hasan et al., 2002;Şener et al., 2000;Mruthyunjayaswamy et al., 2000;Arpaci et al., 2002).

S2. Structural commentary
In the molecule of the title compound ( Fig. 1), the oxygen atom of the nitrone group exists in syn-conformation with respect to the sulfur atom of the benzothiazole moiety. This conformation is achieved due to a strong electrostatic intramolecular attractive S···O interaction. Thus, the S1···O1 distance (2.6977 (16) Å) is significantly shorter than the sum of the van der Waals radii of O and S (1.5 and 1.85 Å, respectively; Wells, 1986). A similar attractive S···O interaction is characteristic for molecules containing the thiazole moiety (Mokhir et al., 2002). The value of the N1-C2 bond length (1.298 (2) Å) is typical for a C═N bond (1.28 Å; Wells, 1986), while the N1-O1 bond length (1.2763 (17) Å) is slightly shorter than those usually observed for nitrone N-O bonds (Petkova et al., 2001;Ruano et al., 2012). The heterocyclic ring system and the nitrone fragment C1-N1-O1-C2 are almost coplanar (the maximum deviation from the leastsquares mean plane is 0.081 (2) Å for atom C1), forming a dihedral angle of 3.40 (9)°. The bond lengths within the benzothiazole ring system are unexceptional.
2-Benzothiazolecarbaldehyde (0.1632 g, 0.01 mol), CH 2 CL 2 (20 ml), and N-metylhydroxylamine hydrochloride (0.9175 g, 0.011 mol) were placed in a 50 mL flask, and the mixture was stirred at room temperature. To the resulting solution supporting information sup-2 Acta Cryst. (2015). E71, o578-o579 was added NaHCO 3 (2.7675 g, 0.033 mol). The reaction mixture was reluxed for 3 h. The NaCl precipitate and excess of sodium bicarbonate was removed by filtration, and the filtrate was evaporated to give a solid (1.83g, yield 95%). The solid was recrystallized from an absolute hexane solution.

S5. Refinement
One aromatic H atom (H6) could be located in a difference Fourier map and was refined freely. All other H atoms were placed geometrically and treated as riding, with C-H = 0.93-0.96 Å, and U iso (H) = 1.5U eq (C) for methyl H atoms or 1.2U eq (C) otherwise. A rotating model was used for the methyl H atoms. 36 outliers were omitted in the last cycles of refinement.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level.