N-(2,4,6-Trichlorophenyl)maleamic acid

In the crystal structure of the title compound, C10H6Cl3NO3, the conformation of the amide bond is trans. The C=O and O—H bonds of the acid group are in the relatively rare anti position to each other. This is a consequence of the intramolecular O—H⋯O hydrogen bond donated to the amide carbonyl group stabilizing the molecular structure. In the crystal, intermolecular N—H⋯O hydrogen bonds link the molecules into zigzag chains along the c axis.

In the crystal structure of the title compound, C 10 H 6 Cl 3 NO 3 , the conformation of the amide bond is trans. The C O and O-H bonds of the acid group are in the relatively rare anti position to each other. This is a consequence of the intramolecular O-HÁ Á ÁO hydrogen bond donated to the amide carbonyl group stabilizing the molecular structure. In the crystal, intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into zigzag chains along the c axis.

Comment
The amide moiety is an important constituent of many biologically significant compounds. As part of our studies on the effects of ring and side chain substitutions on the structures and other aspects of N-(aryl)-amides (Arjunan et al., 2004;Bhat & Gowda, 2000;Gowda et al., 2000Gowda et al., , 2009Prasad et al., 2002) and N-(aryl)-methanesulfonamides (Jayalakshmi & Gowda, 2004), the crystal structure of N-(2,4,6-trimethylphenyl)-maleamic acid (I) has been determined. The conformation of the amide O atom is anti to the H atom attached to the adjacent C atom, while the carboxyl O atom is syn to the H atom attached to its adjacent C atom (Fig.1). The rare anti conformation of the C=O and O-H bonds of the acid group has been observed, similar to that obsrved in N-(2,4,6-trimethylphenyl)-maleamic acid (Gowda et al., 2009) and N-phenylmaleamic acid (Lo & Ng, 2009), but contrary to the more general syn conformation observed for C=O and O-H bonds. The various modes of interlinking carboxylic acids by hydrogen bonds is described elsewhere (Leiserowitz, 1976).
The maleamic moiety includes a short intramolecular hydrogen O-H···O bond ( Table 1). The C8-C9 bond length of 1.331 (3)Å clearly indicates the double bond character. The dihedral angle between the phenyl ring and the amido group -NHCO-is 83.2 (2)°. In the crystal structure, the intermolecular N-H···O hydrogen bonds link the molecules into column like chains along b-axis (Fig. 2).

Experimental
The solution of maleic anhydride (0.025 mol) in toluene (25 ml) was treated dropwise with the solution of 2,4,6-trichloroaniline (0.025 mol) also in toluene (20 ml) with constant stirring. The resulting mixture was stirred for about 30 min and set aside for an additional 30 min at room temperature for the completion of reaction. The mixture was then treated with dilute hydrochloric acid to remove the unreacted 2,4,6-trichloroaniline. The resultant solid N-(2,4,6-trichlorophenyl)maleamic acid was filtered under suction and washed thoroughly with water to remove the unreacted maleic anhydride and maleic acid. It was recrystallized to constant melting point from ethanol. The purity of the compound was checked and characterized by its infrared spectra.
Prism like colorless single crystals used in X-ray diffraction studies were grown in an ethanol solution by slow evaporation at room temperature.

Refinement
The H atoms of the NH group and the OH group were located in a difference map and later restrained to the distance N-H   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.