2,3,5,6-Tetra­chloro­benzene-1,4-dicarboxylic acid

The title compound, C₈H₂Cl₄O₄, was synthesized by the reaction of 2,3,5,6-tetra­chloro­benzene-1,4-dicarbonitrile and sulfuric acid. The mol­ecule is located across an inversion center. The carboxyl group is tilted with respect to the benzene ring by an angle of 72.42 (7)°. Inter­molecular O—H...O hydrogen bonding helps to stabilize the crystal structure.

Key indicators

• Single-crystal X-ray study
• T = 296 K
• Mean [sigma](C-C)= 0.002 Å
• R factor = 0.024
• wR factor = 0.064
• Data-to-parameter ratio = 16.4

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S1. Comment

2,3,5,6-Tetrachlorobenzene-1,4-dicarboxylic acid is an important intermediate which can be used for the synthesis of herbicides (Eufemia & Epel, 1998; Meazza et al., 2007). This paper presents the results of the single-crystal X-ray diffraction analysis of the title compound. A perspective view of the title compound is shown in Fig. 1. The bond lengths and angles are within normal ranges. In the molecule, the carboxyl group forms a dihedral angle of 72.42 (7)° with the central benzene ring. Classical intermolecular O—H···O hydrogen bonding occurs in the crystal structure (Table 1 and Fig. 2), which may be effective in the stabilization of the crystal structure. Short intermolecular Cl···Cl(1/2 - x,1/2 + y,1/2 - z) contact of 3.62 (8) Å is observed in the crystal structure.

Related literature

For general background, see: Eufemia & Epel (1998); Meazza et al. (2007).

S2. Experimental

2,3,5,6-Tetrachlorobenzene-1,4-dicarbonitrile (26.5 g, 100 mmol) was mixed with concentrated sulfuric acid (240 ml) and water (60 ml) under reflux at 463 K for 36 h. Upon standing this solution yielded crystalline 2,3,5,6-tetrachlorobenzene-1,4-dicarboxylic acid, which was filtered, washed with water (2× 50 ml), and dried under vacuum for 24 h (19.2 g, 63.2% yield). Single crystals were obtained by slow evaporation of the aqueous solution.

S3. Refinement

H atom was placed in calculated position with O—H = 0.82 Å and refined in riding mode, U_iso(H) = 1.5U_eq(O).

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL (Bruker, 2000); molecular graphics: SHELXTL (Bruker, 2000); software used to prepare material for publication: SHELXTL (Bruker, 2000).

Figures

	Fig. 1. The molecular structure of (I) (thermal ellipsoids are shown at 30% probability levels) [symmetry code: (A) -x, 2 - y, -z].
	Fig. 2. A packing diagram for (I). Dashed lines indicate hydrogen bonds and short intermolecular Cl···Cl contacts.

2,3,5,6-Tetrachlorobenzene-1,4-dicarboxylic acid

Crystal data

C8H2Cl4O4	F(000) = 300.0
Mr = 303.90	Dx = 1.920 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 3424 reflections
a = 5.9852 (9) Å	θ = 3.3–27.6°
b = 7.0349 (10) Å	µ = 1.12 mm^−1
c = 12.7012 (19) Å	T = 296 K
β = 100.668 (2)°	Block, colorless
V = 525.55 (13) Å^3	0.30 × 0.22 × 0.20 mm
Z = 2

Data collection

Bruker SMART CCD area-detector diffractometer	1213 independent reflections
Radiation source: fine-focus sealed tube	1145 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.021
ϕ and ω scans	θmax = 27.6°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	h = −7→7
Tmin = 0.734, Tmax = 0.800	k = −9→8
4350 measured reflections	l = −16→16

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.024	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.064	H-atom parameters constrained
S = 1.01	w = 1/[σ^2(Fo^2) + (0.03P)^2 + 0.2817P] where P = (Fo^2 + 2Fc^2)/3
1213 reflections	(Δ/σ)max < 0.001
74 parameters	Δρmax = 0.32 e Å^−3
0 restraints	Δρmin = −0.23 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Cl1	0.27187 (7)	1.04641 (6)	0.19970 (3)	0.04105 (13)
Cl2	0.10264 (7)	0.73074 (6)	0.02950 (3)	0.03963 (13)
O1	0.4028 (2)	0.53756 (15)	−0.12663 (9)	0.0455 (3)
H1	0.3466	0.4605	−0.1724	0.068*
O2	0.2347 (2)	0.74573 (15)	−0.24712 (9)	0.0395 (3)
C2	0.3240 (2)	0.87853 (19)	0.01385 (10)	0.0272 (3)
C1	0.3983 (2)	1.01943 (19)	0.08955 (10)	0.0270 (3)
C3	0.4255 (2)	0.85885 (18)	−0.07583 (10)	0.0265 (3)
C4	0.3431 (2)	0.70930 (19)	−0.15941 (11)	0.0289 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cl1	0.0506 (2)	0.0444 (2)	0.0328 (2)	−0.00380 (17)	0.01984 (16)	−0.00767 (15)
Cl2	0.0409 (2)	0.0375 (2)	0.0414 (2)	−0.01307 (15)	0.00999 (16)	−0.00066 (15)
O1	0.0733 (8)	0.0230 (5)	0.0330 (6)	0.0063 (5)	−0.0091 (5)	−0.0043 (4)
O2	0.0572 (7)	0.0265 (5)	0.0294 (5)	−0.0020 (5)	−0.0064 (5)	0.0004 (4)
C2	0.0303 (6)	0.0229 (6)	0.0280 (6)	−0.0014 (5)	0.0044 (5)	0.0008 (5)
C1	0.0325 (7)	0.0256 (6)	0.0232 (6)	0.0019 (5)	0.0063 (5)	−0.0010 (5)
C3	0.0340 (7)	0.0207 (6)	0.0234 (6)	0.0017 (5)	0.0015 (5)	−0.0012 (5)
C4	0.0376 (7)	0.0230 (6)	0.0256 (6)	−0.0002 (5)	0.0041 (5)	−0.0015 (5)

Geometric parameters (Å, º)

Cl1—C1	1.7199 (14)	C2—C3	1.3936 (19)
Cl2—C2	1.7243 (14)	C2—C1	1.3951 (18)
O1—C4	1.3060 (17)	C1—C3^i	1.394 (2)
O1—H1	0.8200	C3—C4	1.5110 (18)
O2—C4	1.2084 (18)
C4—O1—H1	109.5	C2—C3—C1^i	119.70 (12)
C3—C2—C1	120.15 (12)	C2—C3—C4	120.56 (12)
C3—C2—Cl2	119.66 (10)	C1^i—C3—C4	119.73 (12)
C1—C2—Cl2	120.18 (10)	O2—C4—O1	123.97 (13)
C3^i—C1—C2	120.15 (12)	O2—C4—C3	123.35 (12)
C3^i—C1—Cl1	119.39 (10)	O1—C4—C3	112.69 (11)
C2—C1—Cl1	120.45 (11)
Cl2—C2—C1—C3^i	−178.81 (10)	Cl2—C2—C3—C4	0.05 (18)
C3—C2—C1—Cl1	179.28 (10)	C2—C3—C4—O2	107.13 (17)
Cl2—C2—C1—Cl1	0.47 (16)	C1^i—C3—C4—O2	−71.6 (2)
Cl2—C2—C3—C1^i	178.82 (10)	C2—C3—C4—O1	−73.18 (17)
C1—C2—C3—C4	−178.76 (12)	C1^i—C3—C4—O1	108.05 (15)

Symmetry code: (i) −x+1, −y+2, −z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O2^ii	0.82	1.84	2.6410 (15)	166

Symmetry code: (ii) −x+1/2, y−1/2, −z−1/2.