4-Amino-2-chlorobenzoic acid

The title compound, C7H6ClNO2, crystallizes with two roughly planar molecules in the asymmetric unit (r.m.s. deviations = 0.073 and 0.074 Å). The amine H atoms of the two molecules have opposite orientations. In the crystal, molecules are linked into dimers by pairs of O—H⋯O hydrogen bonds, generating R 2 2(8) loops. N—H⋯N and N—H⋯Cl hydrogen bonds link the dimers into a three-dimensional network. The crystal studied was found to be a racemic twin.

The title compound, C 7 H 6 ClNO 2 , crystallizes with two roughly planar molecules in the asymmetric unit (r.m.s. deviations = 0.073 and 0.074 Å ). The amine H atoms of the two molecules have opposite orientations. In the crystal, molecules are linked into dimers by pairs of O-HÁ Á ÁO hydrogen bonds, generating R 2 2 (8) loops. N-HÁ Á ÁN and N-HÁ Á ÁCl hydrogen bonds link the dimers into a three-dimensional network. The crystal studied was found to be a racemic twin.
The amine H atoms of the two molecules have opposite orientations. In the crystal, the molecules form dimers via intermolecular O-H···O hydrogen bonds, forming a graph-set motif R 2 2 (8) (Bernstein et al., 1995; Table 1, Fig. 2). Furthermore, C-H···O, N-H···N and N-H···Cl interactions stabilize the crystal structure.

Experimental
To a 100-ml round bottom flask equipped with a reflux condenser, was placed 0.5 g (2.486 mmol) of 2-chloro-4-amino benzoic acid and 0.447 g m of granulated tin. Then, 30 ml of concentrated HCl in was added in six intervals (5 ml each time with cooling in ice). The reaction is highly exothermic and the reaction mixture is keept under control by keeping it in ice water. When all the HCl was added and the temprature of the reaction mixture was stable, the round bottom flask was placed on water bath for 90 min under reflux.
TLC check after 90 min showed completion of reaction. Reaction mixtures was treated with 60% NaOH solution followed by the addition of NaCl solution and extration with di-ethyl ether.
Diethyl ether was evaporated on rotary evaporator and reddish brown precipates of the required product were obtained.
This was recrystallized in methanol to yield reddish brown prisms of (I).

Refinement
The H atoms of the NH 2 and OH groups in the title compound were located in a difference map and refined with the distance restraint N--H = 0.86 (1) and O--H = 0.82 (1) Å; their U iso values were constrained to be 1.5U eq of the carrier atom for hydroxyl H atoms and 1.2U eq for amine H atoms. The remaining aromatic H atoms were positioned geometrically with C-H = 0.93 Å, and refined using a riding model, with U iso (H) = 1.2U eq (C). The crystal studied was a racemic twin [Flack parameter = 0.50 (6)].