2-Amino-3,4,5,6-tetra­fluoro­benzoic acid

Xiao-Jian Liao; Wei Guo; Shi-Hai Xu

doi:10.1107/S1600536811023087

. 2011 Jun 18;67(Pt 7):o1732. doi: 10.1107/S1600536811023087

2-Amino-3,4,5,6-tetrafluorobenzoic acid

Xiao-Jian Liao ^a, Wei Guo ^a, Shi-Hai Xu ^a,^*

PMCID: PMC3151811 PMID: 21837121

Abstract

The asymmetric unit of the title compound, C₇H₃F₄NO₂, obtained as an intermediate in the synthesis of a coupling reagent, contains four independent and conformationally similar molecules. The amine H atoms form both intramolecular and intermolecular N—H⋯O_carboxyl hydrogen bonds which, together with intermolecular O—H⋯O_carboxyl hydrogen bonds and N—H⋯F associations form ribbon structures along the a axis.

Related literature

The title compound was obtained as one of the intermediates in the synthesis of a coupling reagent (Xu et al., 2008 ▶; Liao et al., 2007 ▶), using the Hofmann rearrangement (Perumal & Muthialu, 2004 ▶) with 2-carboxyl-3,4,5,6-tetrafluorobenzamide (Cai et al., 1992 ▶).

Experimental

Crystal data

C₇H₃F₄NO₂
M _r = 209.10
Triclinic,
a = 11.0367 (11) Å
b = 11.3664 (11) Å
c = 12.5702 (12) Å
α = 80.378 (8)°
β = 79.764 (8)°
γ = 82.011 (8)°
V = 1520.2 (3) Å³
Z = 8
Cu Kα radiation
μ = 1.79 mm⁻¹
T = 295 K
0.50 × 0.30 × 0.15 mm

Data collection

Oxford Diffraction Xcalibur Sapphire3 Gemini ultra CCD diffractometer
Absorption correction: multi-scan (CrysAlis PRO; Oxford Diffraction, 2010 ▶) T _min = 0.392, T _max = 1.000
8708 measured reflections
4791 independent reflections
3521 reflections with I > 2σ(I)
R _int = 0.031

Refinement

R[F ² > 2σ(F ²)] = 0.057
wR(F ²) = 0.177
S = 1.05
4791 reflections
533 parameters
16 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.43 e Å⁻³
Δρ_min = −0.24 e Å⁻³

Data collection: CrysAlis PRO (Oxford Diffraction, 2010 ▶); cell refinement: CrysAlis PRO; data reduction: CrysAlis PRO; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: OLEX2 (Dolomanov et al., 2009 ▶); software used to prepare material for publication: OLEX2.

Supplementary Material

Crystal structure: contains datablock(s) global. DOI: 10.1107/S1600536811023087/zs2117sup1.cif

e-67-o1732-sup1.cif^{(23.6KB, cif)}

Supplementary material file. DOI: 10.1107/S1600536811023087/zs2117globalsup2.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1B⋯O4	0.84 (3)	2.04 (4)	2.637 (4)	128 (3)
N1—H1B⋯F5ⁱ	0.84 (3)	2.40 (3)	3.154 (4)	150 (3)
N2—H2A⋯O10ⁱⁱ	0.83 (3)	2.58 (3)	3.363 (5)	158 (3)
N2—H2B⋯O7	0.85 (3)	2.03 (4)	2.643 (5)	129 (3)
N3—H3A⋯O11ⁱⁱⁱ	0.85 (3)	2.50 (3)	3.337 (4)	167 (3)
N3—H3B⋯O5	0.85 (3)	2.04 (4)	2.654 (4)	129 (3)
N4—H4B⋯O1	0.86 (3)	2.01 (3)	2.648 (4)	130 (3)
N4—H4B⋯F16^iv	0.86 (3)	2.48 (3)	3.191 (5)	140 (3)
O9—H9⋯O5^v	0.82	1.84	2.660 (3)	175
O10—H10⋯O4^vi	0.82	1.86	2.675 (4)	178
O11—H11⋯O1^vi	0.82	1.82	2.643 (3)	177

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

Acknowledgments

This work was supported by grants from the National High Technology Development Project (863 Project; Nos. 2006 A A09Z408 GDSFC 06025194, 2005 A30503001, and 2006Z3E4041) and the National Natural Science Fund (No. 20772048)

supplementary crystallographic information

Comment

The title compound C₇H₃F₄NO₂ (I) was obtained as one of the intermediates in the synthesis of a coupling reagent (Xu et al., 2008, Liao et al., 2007), using the Hofmann rearrangement (Perumal & Muthialu, 2004) with 2-carboxyl-3,4,5,6-tetrafluorobenzamide (Cai et al., 1992). In the structure of (I), the asymmetric unit contains four independent and conformationally similar molecules (Fig. 1). The molecules associate through carboxylic acid O—H···O_carboxyl hydrogen bonds (Table 1) while the amine H atoms form both intramolecular N—H···O_carboxyl hydrogen bonds as well as intermolecular N—H···F associations give one-dimensional ribbon structures. Also present in the structure are short intermolecular F···F contacts [minimum, 2.825 (3) Å].

Experimental

To a stirred solution of 39.2 g of KOH in 356 mL of distilled water, 11.3 g of bromine was added and after 30 min, 70 mmol of 2-carboxy-3,4,5,6-tetrafluorobenzamide was added. After allowing the reaction to proceed for 30 min at 293 K, the mixture was heated to 363K-368K and maintained at that temperature for 4 h, after which the mixture was cooled to room temperature and allowed to stand for 48 h. To the mixture was then added 100 mL of water, the pH adjusted to 1 at ice-water temperature, stirred and filtered, giving a yellow solid (16.2 g, yield 94%). Pale yellow crystals of (I) suitable for X-ray analysis grew over a period of a week from a solution of the solid in methanol at room temperature.