N-(4-Methylphenylsulfonyl)maleamic acid

In the title compound, C11H11NO5S, the dihedral angle between the benzene ring and the amide group is 76.88 (6)°. In the crystal, N—H⋯O(S) and O—H⋯O hydrogen bonds connect the molecules into hydrogen-bonded layers perpendicular to the a axis.


Related literature
The conformations of the N-H and C═O bonds in the amide segment are anti to each other and the amide C═O is syn to the adjacent C-H bond. Further, the amide C═O and the carboxyl C═O of the acid segment orient themselves almost perpendicular to each other, in contrast to the almost anti conformation observed between the amide C═O and the carboxyl C═O in N-(4-methylphenylsulfonyl)-succinamic acid (Purandara et al., 2012). In the title compound, the C-H bonds on the -CH═ CH-group, adjacent to both the C═bonds, are syn to each other.
In the title compound, the C═O and O-H bonds of the acid group are in syn position to each other, similar to that observed in N-(4-methylphenylsulfonyl)-succinamic acid.
The molecule is bent at the S-atom with an C1-S1-N1-C7 torsion angle of 64.99 (13)°. Further, the dihedral angle between the phenyl ring and the amide group is 76.88 (6)°.
In the crystal, the intermolecular O-H···O and N-H···O(S) hydrogen bonds link the molecules into dimers and chains, respectively. The chains and dimers, in combination, form H-bonded layers perpendicular to the a-axis (Fig.2).

Experimental
Maleic anhydride (0.015 mole) and triethylamine (0.01 mole) were added to a solution of p-toluenesulfonamide (0.01 mole) in dichloromethane. The reaction mixture was strirred for 18 h at room temperature and set aside for completion of the reaction. The reaction mixture was concentrated to dryness. The resultant title compound was washed with dilute HCl and then with water thoroughly, to remove the unreacted base and the maleic anhydride. It was recrystallized to constant melting point from ethyl acetate (144°C). The purity of the compound was checked and characterized by its IR spectrum.
Prism like colorless single crystals used in the X-ray diffraction study were grown from ethyl acetate solution by slow evaporation of the solvent.

Refinement
H atoms bonded to C were positioned with idealized geometry using a riding model with the aromatic C-H = 0.93 Å, methyl C-H = 0.96 Å. The amino H atom and the H atom of the OH group were freely refined with O-H = 0.91 (2) Å while the N-H distance later was restrained to 0.86 (2) Å, respectively. All H atoms were refined with isotropic displacement parameters set at 1.2 U eq (C-aromatic, N) and 1.5 U eq (C-methyl, O-hydroxyl) of the parent atom. The (4 0 0   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 R-factors(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.