3-Chloro-2,4,5-trifluorobenzoic acid

The title compound, C7H2ClF3O2, was prepared by the chlorination of 3-amino-2,4,5-trifluorobenzoic acid. The carboxyl group is twisted relative to the benzene ring by 6.8 (1)°. In the crystal, pairs of O—H⋯O hydrogen bonds link molecules into typical centrosymmetric carboxylic acid dimers. These dimers are arranged into sheets parallel to (-103).

The title compound, C 7 H 2 ClF 3 O 2 , was prepared by the chlorination of 3-amino-2,4,5-trifluorobenzoic acid. The carboxyl group is twisted relative to the benzene ring by 6.8 (1) . In the crystal, pairs of O-HÁ Á ÁO hydrogen bonds link molecules into typical centrosymmetric carboxylic acid dimers. These dimers are arranged into sheets parallel to (103).

Related literature
For applications of the title compound in synthesis, see: Sun et al. (2011). For a related structure, see: Zhu (2009 Table 1 Hydrogen-bond geometry (Å , ).
In the title molecule ( Fig. 1) the carboxyl group forms a dihedral angle of 6.8 (1)° with the benzene ring. Intermolecular O-H···O hydrogen bond (Table 1) links the molecules into typical carboxylic acid dimers.

Experimental
A solid mixture of 0.52 g of 3-amino-2,4,5-trifluorobenzoic acid and 0.33 g of sodium nitrite was added in portions to a solution of 3 g of cupric chloride in 9 ml of water and 0.5 g of a 36% aqueous solution of hydrochloric acid. The resulting mixture was stirred for 1.5 h and then additional water (25 ml) and diethyl ether (20 ml) were added. The layers are separated and the aqueous layer extracted with diethyl ether. The combined organic extracts are extracted with 36% aqueous solution of hydrochloric acid and then concentrated on the rotary evaporator to give 0.45 g of 3-chloro-2,4,5trifuorobenzoic acid as a light-brown solid. Crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation of a toluene solution.

Refinement
H atoms were positioned geometrically with O-H = 0.82 Å and C-H = 0.93 Å and constrained to ride on their parent atoms, with U iso (H) =xUeq(C,O), where x = 1.5 for OH and x = 1.2 for CH H atoms.

Computing details
Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS (Enraf-Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).     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.