Methyl 4-bromo-3,5-dinitro­benzoate

The title compound, C₈H₅BrN₂O₆, was synthesized from the nitration of 4-bromo­benzoic acid with fuming nitric acid/sulfuric acid and subsequent esterification by sulfonyl chloride in dry methanol. The NO₂ groups are rotated out of conjugation with the aromatic ring, with dihedral angles of 55.6 (4) and 79.5 (3)°.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.052
• wR factor = 0.179
• Data-to-parameter ratio = 14.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT431_ALERT_2_B Short Inter HL..A Contact  Br1    ..  O1      ..       3.00 Ang.

Alert level C
PLAT029_ALERT_3_C _diffrn_measured_fraction_theta_full Low .......       0.97
PLAT432_ALERT_2_C Short Inter X...Y Contact  O3     ..  C7      ..       3.01 Ang.

   0 ALERT level A = In general: serious problem
   1 ALERT level B = Potentially serious problem
   2 ALERT level C = Check and explain
   0 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   2 ALERT type 2 Indicator that the structure model may be wrong or deficient
   1 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

In the field of anion recognition, host-architectures often incorporate various types of supramolecular interactions. Hydrogen-bonding (Bryantsev & Hay, 2005; Gale et al., 1996), metal coordination (Yang et al., 1991), and electrostatic ion-pairing (Beer & Dent, 1998) or their combination (Park & Simmons, 1968) can be used to form primary binding motifs to target desired guest molecules. Recently, it has been shown that substituted nitro- and cyanobenzenes interact with halides in solution and in the solid state (Berryman et al., 2007; Rosokha et al., 2004). Anions have also been observed to interact with other electron-deficient systems (de Hoog et al., 2004; Demeshko et al., 2004; Frontera et al., 2005; Holman et al., 1996; Schottel et al., 2005; 2006; Staffilani et al., 1997). It is hypothesized that the substitution pattern and combination of electron withdrawing groups heavily govern the strength of the interaction. However, the attractive forces between anions and electron-deficient aromatic systems are not fully understood. Observed and calculated binding geometries contradict purposed electrostatic models and provide support for charge transfer complexes (Berryman et al., 2007; Rosokha et al., 2004).

One challenge in investigating the strength of anion/arene interactions lies in the synthesis of increasingly electron-deficient anionophore architectures. Highly electron-deficient arenes become non-reactive to electrophilic aromatic substitution and may become hazardous and unstable (Lothrope & Handrick, 1949). The synthesis of charge-neutral, electron-deficient arenes likely will aid in developing the supramolecular host–guest chemistry of anions. Herein we report the molecular and crystal structure of the title compound, (2), –an example of an electron-deficient arene– which offers a route to further modification through its aryl halide functionality. Compound (2) has been exploited as an antifungal agent (Lehtonen et al., 1972) and efficiently undergoes homo-coupling in the presence of copper (Ullman & Bielecki, 1901) leading to synthesis of new liquid crystalline materials (Manka et al., 2003).

Compound (2) is a planar molecule (Fig. 2) obtained from the nitration of 4-bromobenzoic acid with fuming nitric acid and sulfuric acid followed by esterification to the methyl ester with sulfonyl chloride and dry MeOH. The deviations of the Br1, N1 and N2 atoms from the average plane of the central 6-membered aromatic ring are 0.026 (6), 0.004 (7) and -0.095 (6) Å, respectively. The nitro groups are rotated out of conjugation with the aromatic ring due to steric constraints imposed by the large bromine atom. The dihedral angles between the N1/O2/O3 and N2/O3/O4 planes and the average plane of the aromatic ring are 55.6 (4)° and 79.5 (3)°, respectively. The ester —C═OOCH₃ group is rotated out this plane by 17.5 (4)°. There are no π···π intermolecular interactions due to NO₂ groups in the aromatic ring, but the short intermolecular Br1···O1(1.5 - x,-1.5 + y,0.5 - z) and O3···C7(1 - x,1 - y,-z) contacts, 2.999 (5) and 3.013 (5) Å, respectively, indicate that intermolecular interactions in the crystal structure are relatively strong. The molecules of (2) form a centrosymmetrical pair via weak C—H···O interactions; the C5···O5(1 - x,2 - y,-z) distance is 3.173 (6) Å (Fig. 3), and pairs are stacked into one-dimensional columns in the crystal structure (Fig. 4).

Related literature

For related literature, see: Beer & Dent (1998); Berryman et al. (2007); Bryantsev & Hay (2005); Demeshko et al. (2004); Frontera et al. (2005); Gale et al. (1996); Holman et al. (1996); de Hoog et al. (2004); Lehtonen et al. (1972); Lothrope & Handrick (1949); Manka et al. (2003); Park & Simmons (1968); Rosokha et al. (2004); Schottel et al. (2005, 2006); Staffilani et al. (1997); Ullman & Bielecki (1901); Yang et al. (1991).

S2. Experimental

4-bromo-3,5-dinitrobenoic acid (1). Fuming nitric acid (5 ml) was added slowly to a stirring solution of concentrated sulfuric acid (20 ml) at 273 K. 4-bromobenzoic acid (4.00 g, 9.05 mmol) was slowly added to the solution. The suspension was heated to 373 K for 10 h. The solution was cooled to room temperature and poured over cracked ice. A white precipitate was filtered off, washed with cold water and dried to yield a fine yellowish crystalline powder (5.69 g, 98.3%). M.p. 454.4–456.6 K; ¹H-NMR (DMSO-d6, 300 MHz) δ 8.51 (s, 2H). ¹³C-NMR (DMSO-d6, 300 MHz) δ 169.08, 156.78, 138.47, 133.35, 116.86.

Methly 4-bromo-3,5-dinitrobenzoate (2). Sulfonyl chloride (4.0 ml, 58 mmol) was added dropwise to 10 ml of dry methanol stirring at 273 K. After 5 minutes at 273 K, 4-bromo-3,5-dinitrobenzoic acid (0.500 g, 1.72 mmol) was added. The suspension was heated at reflux (ca 338 K) for 24 h. The reaction mixture was cooled to room temperature and the off-white solid was filtered and washed with cold methanol. Subsequent recrystallization from hot methanol yielded long white needles (0.280 g, 53.4%). Further product was obtained by evaporation of the remaining mother liquor. The resulting solid was dissolved in ethyl acetate and washed with 4% aqueous sodium hydrogen carbonate (3 x 10 ml) followed by water (10 ml) to remove residual starting material. The organic layer was dried over magnesium sulfate and evaporation of the solvent produced an off-white solid. Recrystallization from hot methanol gave the title compound (0.201 g, 38.4%) as long white needles. (Total yield: 91.8%). M.p. 393.9–394.3 K; ¹H-NMR (CDCl₃, 300 MHz) d 8.51 (s, 2H), 4.02 (s, 3H). ¹³C-NMR (DMSO-d6, 500 MHz) δ 168.2, 156.86, 137.0, 133.2, 117.4, 58.8.

Single crystals suitable for X-ray diffraction were prepared by slow evaporation of a concentrated solution of (2) in tetrahydrofuran at room temperature. After three days crystals appeared as colorless needles.

S3. Refinement

The H atoms were positioned geometrically and refined in the riding model approximation, C—H = 0.95 and 0.98 Å; U_iso(H) = 1.2U_eq(C) and 1.5U_eq(C), respectively for aromatic and methyl H atoms.

Computing details

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

Figures

	Fig. 1. Reaction scheme.
	Fig. 2. The molecular structure of (2), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 3. A centrosymmetric pair of molecules. Dashed lines denote aryl C—H hydrogen-bonding associations [3.173 (6) Å]. Displacement ellipsoids are drawn at the 50% probability level. The symmetry-related fragment, labelled with the suffix A, is derived using the symmetry operator (1 - x, 2 - y, -z).
	Fig. 4. A fragment of the crystal structure of (2), showing stacks of molecules.

Methyl 4-bromo-3,5-dinitrobenzoate

Crystal data

C8H5BrN2O6	F(000) = 600
Mr = 305.04	Dx = 1.922 Mg m^−3
Monoclinic, P21/n	Melting point: 394.1 K
Hall symbol: -P 2yn	Mo Kα radiation, λ = 0.71073 Å
a = 9.6350 (9) Å	Cell parameters from 5682 reflections
b = 5.0104 (5) Å	θ = 2.3–27.0°
c = 21.913 (2) Å	µ = 3.92 mm^−1
β = 94.686 (2)°	T = 173 K
V = 1054.31 (18) Å^3	Block, colourless
Z = 4	0.38 × 0.26 × 0.20 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer	2228 independent reflections
Radiation source: fine-focus sealed tube	1938 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.012
φ and ω scans	θmax = 27.0°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Sheldrick, 1995)	h = −12→3
Tmin = 0.285, Tmax = 0.457	k = −5→6
3498 measured reflections	l = −25→27

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)] = 0.052	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.179	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.1272P)^2 + 2.0826P] where P = (Fo^2 + 2Fc^2)/3
2228 reflections	(Δ/σ)max < 0.001
154 parameters	Δρmax = 0.83 e Å^−3
0 restraints	Δρmin = −0.53 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
Br1	0.73453 (5)	0.16258 (10)	0.18421 (2)	0.0323 (2)
O1	0.5247 (5)	0.3004 (9)	0.27993 (17)	0.0462 (11)
O2	0.3348 (4)	0.1773 (7)	0.23145 (17)	0.0331 (8)
O3	0.7443 (4)	0.3120 (7)	0.03565 (17)	0.0297 (8)
O4	0.8423 (3)	0.6612 (7)	0.07736 (18)	0.0343 (9)
O5	0.3398 (3)	1.1689 (6)	0.04798 (15)	0.0217 (7)
O6	0.1825 (3)	0.9699 (7)	0.10260 (15)	0.0266 (7)
N1	0.4462 (4)	0.2973 (7)	0.23679 (18)	0.0230 (8)
N2	0.7466 (3)	0.5060 (7)	0.06887 (15)	0.0189 (7)
C1	0.6013 (4)	0.4070 (8)	0.15411 (18)	0.0168 (8)
C2	0.4783 (4)	0.4520 (8)	0.18125 (17)	0.0173 (8)
C3	0.3788 (4)	0.6324 (8)	0.15781 (19)	0.0188 (8)
H3A	0.2933	0.6519	0.1761	0.023*
C4	0.4060 (4)	0.7841 (8)	0.10722 (19)	0.0164 (8)
C5	0.5278 (4)	0.7439 (8)	0.07845 (19)	0.0168 (7)
H5A	0.5462	0.8448	0.0433	0.020*
C6	0.6212 (4)	0.5548 (8)	0.10203 (17)	0.0153 (7)
C7	0.3073 (4)	0.9972 (8)	0.08195 (18)	0.0184 (8)
C8	0.0813 (5)	1.1733 (10)	0.0832 (3)	0.0348 (12)
H8A	−0.0070	1.1354	0.1007	0.052*
H8B	0.0666	1.1736	0.0384	0.052*
H8C	0.1159	1.3484	0.0974	0.052*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0381 (4)	0.0299 (4)	0.0282 (4)	0.00590 (17)	−0.0007 (2)	0.00055 (17)
O1	0.059 (3)	0.060 (3)	0.0201 (18)	−0.014 (2)	0.0071 (18)	0.0135 (17)
O2	0.0378 (19)	0.032 (2)	0.0309 (19)	−0.0103 (14)	0.0125 (15)	0.0035 (14)
O3	0.0306 (16)	0.0285 (18)	0.0316 (18)	0.0057 (13)	0.0110 (14)	−0.0095 (14)
O4	0.0213 (16)	0.040 (2)	0.043 (2)	−0.0047 (13)	0.0103 (14)	−0.0078 (16)
O5	0.0199 (14)	0.0210 (16)	0.0248 (17)	0.0025 (10)	0.0056 (12)	0.0026 (11)
O6	0.0141 (13)	0.0338 (18)	0.0330 (17)	0.0068 (12)	0.0081 (12)	0.0073 (14)
N1	0.0278 (19)	0.0154 (17)	0.028 (2)	−0.0036 (14)	0.0162 (16)	−0.0050 (15)
N2	0.0141 (14)	0.0261 (19)	0.0170 (16)	0.0059 (13)	0.0041 (12)	0.0025 (14)
C1	0.0208 (17)	0.0140 (18)	0.0156 (19)	−0.0002 (15)	0.0008 (14)	−0.0022 (15)
C2	0.0237 (18)	0.0165 (19)	0.0121 (18)	−0.0031 (15)	0.0043 (14)	−0.0002 (15)
C3	0.0173 (17)	0.023 (2)	0.017 (2)	−0.0018 (15)	0.0067 (14)	−0.0042 (16)
C4	0.0134 (17)	0.0180 (19)	0.0182 (19)	0.0009 (14)	0.0034 (14)	−0.0013 (16)
C5	0.0167 (17)	0.0182 (19)	0.0163 (17)	0.0003 (15)	0.0055 (14)	−0.0007 (15)
C6	0.0133 (16)	0.0187 (19)	0.0141 (18)	0.0002 (14)	0.0037 (13)	−0.0022 (15)
C7	0.0163 (17)	0.023 (2)	0.0163 (19)	0.0026 (15)	0.0024 (14)	−0.0050 (16)
C8	0.0150 (19)	0.040 (3)	0.049 (3)	0.0105 (18)	0.0040 (19)	0.008 (2)

Geometric parameters (Å, º)

Br1—C1	1.856 (4)	C1—C2	1.387 (5)
O1—N1	1.162 (6)	C2—C3	1.386 (6)
O2—N1	1.227 (5)	C3—C4	1.386 (6)
O3—N2	1.214 (5)	C3—H3A	0.9500
O4—N2	1.209 (5)	C4—C5	1.392 (5)
O5—C7	1.196 (5)	C4—C7	1.505 (5)
O6—C7	1.327 (5)	C5—C6	1.378 (6)
O6—C8	1.450 (5)	C5—H5A	0.9500
N1—C2	1.496 (5)	C8—H8A	0.9800
N2—C6	1.481 (4)	C8—H8B	0.9800
C1—C6	1.387 (6)	C8—H8C	0.9800
C7—O6—C8	115.7 (3)	C3—C4—C7	121.9 (3)
O1—N1—O2	126.2 (4)	C5—C4—C7	117.8 (4)
O1—N1—C2	119.4 (4)	C6—C5—C4	118.6 (4)
O2—N1—C2	114.4 (4)	C6—C5—H5A	120.7
O4—N2—O3	125.7 (3)	C4—C5—H5A	120.7
O4—N2—C6	117.5 (3)	C5—C6—C1	123.1 (3)
O3—N2—C6	116.8 (3)	C5—C6—N2	117.6 (3)
C6—C1—C2	116.5 (4)	C1—C6—N2	119.3 (3)
C6—C1—Br1	120.5 (3)	O5—C7—O6	125.3 (4)
C2—C1—Br1	123.0 (3)	O5—C7—C4	123.4 (3)
C3—C2—C1	122.5 (4)	O6—C7—C4	111.4 (3)
C3—C2—N1	117.2 (3)	O6—C8—H8A	109.5
C1—C2—N1	120.3 (4)	O6—C8—H8B	109.5
C2—C3—C4	118.9 (4)	H8A—C8—H8B	109.5
C2—C3—H3A	120.5	O6—C8—H8C	109.5
C4—C3—H3A	120.5	H8A—C8—H8C	109.5
C3—C4—C5	120.3 (4)	H8B—C8—H8C	109.5
C6—C1—C2—C3	0.6 (6)	C4—C5—C6—N2	177.0 (4)
Br1—C1—C2—C3	−179.1 (3)	C2—C1—C6—C5	2.0 (6)
C6—C1—C2—N1	178.6 (3)	Br1—C1—C6—C5	−178.3 (3)
Br1—C1—C2—N1	−1.1 (5)	C2—C1—C6—N2	−176.7 (3)
O1—N1—C2—C3	−125.8 (5)	Br1—C1—C6—N2	3.0 (5)
O2—N1—C2—C3	53.9 (5)	O4—N2—C6—C5	80.3 (5)
O1—N1—C2—C1	56.1 (6)	O3—N2—C6—C5	−100.0 (4)
O2—N1—C2—C1	−124.2 (4)	O4—N2—C6—C1	−100.9 (5)
C1—C2—C3—C4	−3.4 (6)	O3—N2—C6—C1	78.8 (5)
N1—C2—C3—C4	178.5 (4)	C8—O6—C7—O5	−2.3 (6)
C2—C3—C4—C5	3.7 (6)	C8—O6—C7—C4	177.2 (4)
C2—C3—C4—C7	−175.7 (4)	C3—C4—C7—O5	162.8 (4)
C3—C4—C5—C6	−1.2 (6)	C5—C4—C7—O5	−16.6 (6)
C7—C4—C5—C6	178.2 (4)	C3—C4—C7—O6	−16.7 (6)
C4—C5—C6—C1	−1.7 (6)	C5—C4—C7—O6	164.0 (4)