3-(2H-Benzotriazol-2-yl)-2-hydroxy-5-methylbenzaldehyde

In the title compound, C14H11N3O2, the dihedral angle between the mean planes of the benzotriazole ring system and the benzene ring of the salicylaldehyde group is 2.4 (2)°. There is an intramolecular O—H⋯N hydrogen bond which may influence the molecular conformation.

In the title compound, C 14 H 11 N 3 O 2 , the dihedral angle between the mean planes of the benzotriazole ring system and the benzene ring of the salicylaldehyde group is 2.4 (2) . There is an intramolecular O-HÁ Á ÁN hydrogen bond which may influence the molecular conformation.   Table 1 Hydrogen-bond geometry (Å , ). These NNO-tridentate Schiff-base ligands were easily prepared by condensation from primary amine with the pendant arm of the amino group and various substituted salicylaldehyde derivatives in the presence of MgSO 4 . The additional amino group can be able to provide strong coordination to stabilize Zn or Mg atom and thereby stabilizes the zinc or magnesium alkoxide complex, without further disproportionation. Most recently, our group has successfully synthesized and structural characterized the amino-phenolate ligand derived from 4-methyl-2-(2H-benzotriazol-2-yl)-phenol (BTP-H) (Li et al., 2009).

Related literature
In order to develop more useful ligands originated from BTP derivates, our group is interested in the preparation of the multidentate Schiff-base ligand containing the benzotriazol group. Herein, we report the synthesis and crystal structure of the title compound, (I), a potential precursor for the preparation of the multidentate Schiff-base BTP ligands.
The molecular structure of (I) reveals the 5-methylsalicylaldehyde configuration with one benzotriazole functionalized group on the C2-position (Fig. 1). The dihedral angle between the planes of the benzotriazole unit and the benzene ring of the salicylaldehyde group is 2.4 (2)°. There is an intramolecular O-H···N hydrogen bond between the phenol and benzotriazole groups ( Table 1). The distance of N1···H1A is substantially shorter than the van der Waals distance of 2.75 Å for the N and H distance. The distances in the benzotriazole-phenolate group are similar to those found in the crystal structure of 2-(2H-benzotriazol-2-yl)-6-((diethylamino)methyl)-4-methylphenol (Li et al., 2009).

Experimental
The title compound (I) was synthesized by the following procedures ( Fig. 2): In a 100 ml round bottom flask was placed with 4-methyl-2-(2H-benzotriazol-2-yl)phenol (4.50 g, 20.0 mmol) and hexamethylenetetramine (5.60 g, 40 mmol). To this was added trifluoroacetic acid (24 ml, 0.30 mol) and the yellow solution became hot. The resulting mixture was heated to 418 K under reflux for 18 h, during which time the solution colour turned the yellow to dark brown/black. The hot solution was poured into 4 N HCl (aq) (40 ml) and stirred for another 2 h, during which time the solids were formed. The mixture was placed at 253 K overnight and the solids were filtered. The mixture was then extracted with dichloromethane (3 x 150 ml) and the organic layers were dried over MgSO 4 . The final solution was removed the solvent under vacuum to give yellow solids. Yield: 4.40 g (87 %). Single crystals suitable for X-ray diffraction were obtained from a saturated solution of the title compound in Et 2 O.

Refinement
The H atoms were placed in idealized positions and constrained to ride on their parent atoms, with C-H = 0.93 Å with U iso (H) = 1.2 U eq (C) for phenyl hydrogen; 0.96 Å with U iso (H) = 1.5 U eq (C) for CH 3 group; 0.93 Å with U iso (H) = 1.2 U eq (C) for CHO group; O-H = 0.85 Å with U iso (H) = 1.2 U eq (C).  Fig. 1. The molecular structure of (I) with the atom numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. The dashed lines indicates a hydrogen bond.  Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
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.