Crystal structures of 2-amino-2-oxoethyl 4-bromobenzoate, 2-amino-2-oxoethyl 4-nitrobenzoate and 2-amino-2-oxoethyl 4-aminobenzoate monohydrate

The title molecules were synthesized by the reaction of the corresponding sodium benzoate with chloroacetic acid amide. Single crystals were obtained from the reaction products under the same conditions.

The title molecules were synthesized by the reaction of 4-substituted sodium benzoates with chloroacetic acid amide in the presence of dimethylformamide. The yields of 2-amino-2-oxoethyl 4-bromobenzoate, C 9 H 8 BrNO 3 , I, 2-amino-2oxoethyl 4-nitrobenzoate, C 9 H 8 N 2 O 5 , II, and 2-amino-2-oxoethyl 4-aminobenzoate monohydrate, C 9 H 10 N 2 O 3 ÁH 2 O, III, are 86, 78 and 88%, respectively. The low yield of II is explained by the reduced reactivity of the molecule in a nucleophilic exchange reaction because of the negative induction and negative mesomeric effects of the nitro group on the benzene ring. Single crystals were obtained from the products under the same (temperature and solvent) conditions. In the case of III, the crystals formed as a monohydrate. In all three crystal structures, the same type of intermolecular N-HÁ Á ÁO hydrogen bonds are observed, but the molecules differ in some torsion angles as well as in the dihedral angles between the mean planes of the benzene rings and the amide groups.

Chemical context
Molecules containing an aromatic ring, a carboxyl and an amino group represent an important class of organic compounds and, with several reaction centers, they are important intermediates in industry. They are often used as synthons in organic synthesis and are also widely used as ligands in the coordination chemistry of various transition metals. These ligands can form a variety of complex compounds as they possess several Lewis base sites.

Structural commentary
All of the title structures have planar benzoate (C1-C7/O1/ O2) and amide (O3/C9/N1) units but the dihedral angle between these planes is different in each case because of the torsion angle about the bridging methylene group (C8; Tables 1-3). The asymmetric unit of each crystal structure is illustrated in Fig. 2. That of I consists of two independent molecules (A and B), which differ in the position of the amide groups relative to the benzoate (r.m.s. deviations of 0.021 Å for A and 0.031 Å for B) fragments, as indicated by the dihedral angles of 82.5 (4) and 75.9 (3) in A and B, respectively. The asymmetric unit of II contains only one molecule of 2-amino-2-oxoethyl 4-nitrobenzoate. The dihedral angle between the mean planes of the amide and the benzoate (r.m.s. deviation = 0.070 Å ) groups is 89.4 (2) . The asymmetric unit of III contains one water molecule and one 2-amino-2-oxoethyl 4-aminobenzoate molecule (Fig. 2). The dihedral angle between the mean planes of the amide and benzoate (r.m.s. deviation = 0.027 Å ) groups is 4.4 (5) . Analysis of the bond lengths and bond angles of I-III shows slight differences, but these data are in the expected ranges (Allen et al., 1987).

Supramolecular features
In the crystal structures, several types of intermolecular interactions are observed but all contain intermolecular N-HÁ Á ÁO hydrogen bonds.

Figure 2
The asymmetric units of I-III with atom labelling. Displacement ellipsoids are drawn at the 30% probability level. Table 1 Selected torsion angles ( ) for (I).
In III, as in II, inversion dimers are formed by N1-H1Á Á ÁO3 i hydrogen bonds (Fig. 5, Table 6). An intermolecular hydrogen bond is also observed between the oxygen of the amide fragment and the water molecule (Fig. 6), although the angle is only 101 , and the water molecules are further connected by hydrogen bonds to form an infinite chain along the b-axis direction.  Table 5 Hydrogen-bond geometry (Å , ) for (II). Hydrogen bonds and intermolecular OÁ Á ÁO contacts in II.

Figure 3
Hydrogen bonds (formation of rings) and intermolecular BrÁ Á ÁBr contacts in I.
Each compound was dissolved in ethanol and the solvent allowed to evaporate at room temperature. Colourless crystals suitable for X-ray diffraction analysis were obtained.
The crystal of the 2-amino-2-oxoethyl 4-aminobenzoate monohydrate loses its transparency without chemical change (without becoming amorphous) in the range 344-346 K when the crystals are heated and melts in the range 435-438 K.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 7  Dimer formation in III.

2-Amino-2-oxoethyl 4-nitrobenzoate (II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.24 e Å −3 Δρ min = −0.29 e Å −3 Special details 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.