N-(3,4-Dichlorophenyl)maleamic acid

The asymmetric unit of the title compound, C10H7Cl2NO3, contains two unique molecules, both being stabilized by an intramolecular O—H⋯O hydrogen bond within their maleamic units. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into chains extending along [1 ] which are further assembled into sheets via short intermolecular C—Cl⋯O=C contacts [3.102 (2) and 3.044 (2) Å].


Comment
In the present work, as a part of studying the effect of ring and side chain substitutions on the crystal structures of biologically significant amides (Gowda et al., 2009(Gowda et al., , 2010Shakuntala et al., 2009;Prasad et al., 2002), the crystal structure of N-(3,4-dichlorophenyl)maleamic acid (I) has been determined (Fig. 1).
The asymmetric unit of the cell contains two molecules. In the first molecule, which significantly deviates from planarity, the torsion angle C6-C5-N1-C1 = 24.9 (3)° defines the orientation of the phenyl ring towards the central amide group -NHCO-. The atoms of maleamic acid moiety do not fit very well to a plane (r.m.s. deviation = 0.077\%A). It makes a dihedral angle of 27.5 (1)° with the phenyl ring. The geometry of the second molecule is almost planar as shown by the small dihedral angle of 1.9 (1)° formed by the planes of phenyl ring and maleamic acid moiety. Each maleamic acid moiety includes a short intramolecular hydrogen bond O-H···O (Table 1). The bond lengths C2-C3 = 1.336 (3) and C22-C23 = 1.333 (3)\%A clearly indicate the double bond character.
In the crystal structure ( Fig. 2), the intermolecular N-H···O hydrogen bonds link the molecules into chains extending along the [1 -1 -1]direction. These chains are further assembled by short Cl···O contacts of the length 3.102 (2) and 3.044 (2)Å to form the sheet like structure.
Our data for the C-Cl···O halogen bonds are in agreement with the observations of others (Fourmigué, 2009, Legon, 1999.

Experimental
The solution of maleic anhydride (0.025 mol) in toluene (25 ml) was treated dropwise with the solution of 3,4-dichloroaniline (0.025 mol) also in toluene (20 ml) with constant stirring. The resulting mixture was warmed with stirring for over 30 min and set aside for an additional 30 min at room temperature for completion of the reaction. The mixture was then treated with dilute hydrochloric acid to remove the unreacted 3,4-dichloroaniline. The resultant solid N-(3,4-dichlorophenyl)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 by elemental analysis and characterized by its infrared spectra.