Ethyl 2-(2,3,4,5,6-Penta­bromo­phen­yl)acetate

Anne M Sauer; Art G Mack; Hassan Y Elnagar; Frank R Fronczek

doi:10.1107/S1600536810025626

. 2010 Jul 14;66(Pt 8):o1994. doi: 10.1107/S1600536810025626

Ethyl 2-(2,3,4,5,6-Pentabromophenyl)acetate

Anne M Sauer ^a, Art G Mack ^a, Hassan Y Elnagar ^a, Frank R Fronczek ^b,^*

PMCID: PMC3007577 PMID: 21588308

Abstract

The title compound PBPEA, C₁₀H₇Br₅O₂, has its ethyl acetate portion nearly orthogonal to the benzene ring, with a C—C—C—C torsion angle of 88.3 (5)°. The packing involves an intermolecular contact with a Br⋯Br distance of 3.491 (1) Å, having C—Br⋯Br angles of 173.4 (2) and 106.0 (2)°. The crystal studied was an inversion twin.

Related literature

For synthetic procedures, see: Holmes & Lightner (1995 ▶); Adams & Thal (1941 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶). For related structures, see: Eriksson & Hu (2002a ▶,b ▶); Eriksson et al. (1999 ▶); Köppen et al. (2007 ▶); Krigbaum & Wildman (1971 ▶); Mrse et al. (2000 ▶); Pedireddi et al. (1994 ▶); Williams et al. (1985 ▶).

Experimental

Crystal data

C₁₀H₇Br₅O₂
M _r = 558.71
Monoclinic,
a = 4.6136 (10) Å
b = 22.548 (5) Å
c = 13.195 (2) Å
β = 90.993 (11)°
V = 1372.4 (5) Å³
Z = 4
Mo Kα radiation
μ = 14.63 mm⁻¹
T = 90 K
0.25 × 0.12 × 0.12 mm

Data collection

Nonius KappaCCD diffractometer with Oxford Cryostream
Absorption correction: multi-scan (SCALEPACK; Otwinowski & Minor, 1997 ▶) T _min = 0.121, T _max = 0.273
10525 measured reflections
3863 independent reflections
3676 reflections with I > 2σ(I)
R _int = 0.013

Refinement

R[F ² > 2σ(F ²)] = 0.025
wR(F ²) = 0.053
S = 1.17
3863 reflections
157 parameters
2 restraints
H-atom parameters constrained
Δρ_max = 0.65 e Å⁻³
Δρ_min = −0.66 e Å⁻³
Absolute structure: Flack (1983 ▶), 1846 Friedel pairs
Flack parameter: 0.467 (13)

Data collection: COLLECT (Nonius, 2000 ▶); cell refinement: SCALEPACK (Otwinowski & Minor, 1997 ▶); data reduction: DENZO (Otwinowski & Minor, 1997 ▶) and SCALEPACK; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536810025626/jj2038sup1.cif

e-66-o1994-sup1.cif^{(16.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810025626/jj2038Isup2.hkl

e-66-o1994-Isup2.hkl^{(189.4KB, hkl)}

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

Acknowledgments

The purchase of the diffractometer was made possible by grant No. LEQSF(1999–2000)-ENH-TR-13, administered by the Louisiana Board of Regents.

supplementary crystallographic information

Comment

In an effort to prepare a series of proposed pentabromophenyl-substituted compounds necessary as analytical standards, the title ethyl ester derivative rendered itself to be an important intermediate and was synthesized via PBBN as an intermediate. This PBBN nitrile precursor was prepared by known procedures (Holmes & Lightner, 1995) from hexabromotoluene, henceforth referred to as pentabromobenzyl bromide, PBBB. Subsequent conversion of the resulting pentabromobenzyl nitrile intermediate to PBPEA was completed with ethanol in sulfuric acid. (Adams & Thal, 1941). The nature of such sterically hindered and electronically deprived pentabromo-compounds has provided a unique opportunity to examine the reactivity and resulting isolation / purification tendencies associated with these systems.

The ethyl acetate portion of the molecule (Fig. 1) is extended, with torsion angles C1—C7—C8—O1 174.8 (3)°, C7—C8—O1—C9 179.3 (3)°, C8—O1—C9—C10 - 165.1 (3)°, and it is nearly orthogonal to the phenyl ring, with C2—C1—C7—C8 torsion angle 88.3 (5)°. The C—Br distances are in the range 1.876 (4)–1.896 (4) Å, with mean value 1.887 Å. This value compares favorably with the mean value of 1.880 Å in decabromodiphenylethane (Köppen et al., 2007), the only ordered entry in the CSD (version 5.31, Nov. 2009; Allen 2002) with Br₅Ph on an sp³ C atom. The structure of pentabromotoluene has also been reported (Krigbaum & Wildman, 1971), but it has the methyl group statistically disordered, sharing all six sites with Br. Structures of several pentabromophenyl ethers have also been reported (Eriksson & Hu, 2002a,b; Eriksson et al., 1999; Mrse et al., 2000; Williams et al., 1985), and the geometries of their Br₅Ph groups are similar.

Packing of compounds containing Br₅Ph groups usually involves intermolecular Br···Br contacts, and one such interaction exists in the structure of the title compound, as illustrated in Fig. 2. The contact is between glide-related molecules, and has Br3···Br5 distance 3.491 (1) Å. The angular disposition of the contact is termed type II by Pedireddi et al. (1994), having one C–Br···Br angle near linear and the other nearly orthogonal. In this case, the angle about Br5 is 173.4 (2)°, and the angle about Br3 is 106.0 (2)°. Also, both O atoms make intermolecular contacts with Br, O1···Br4(1 + x, 1 - y, 1/2 + z) 3.184 (3) Å; O2···Br2 (x - 1/2, 3/2 - y, 1/2 + z) 3.123 (3) Å.

Experimental

Preparation of PBBN (9263–183):(Fig. 3) To a 3-neck, 100-ml RBF, fitted with a nitrogen inlet, thermocouple and septum, was charged the starting PBBB (5 g, 8.84 mmol) in DMSO (50 ml). To this slurry was added the sodium cyanide (0.44 g, 8.98 mmol) in one portion at room temperature and the reaction mixture immediately became mint in color. This color quickly dissipated and became brown. The reaction was allowed to heat for one hour, with vigorous stirring, at 80 °C under an inert atmosphere. Upon conclusion, the contents were filtered hot to remove an insoluble material (1.01 g) and the resulting brown filtrate was treated with water to precipitate the PBBN product. The light brown solids (fluffy) were collected via suction filtration. Drying overnight afforded a dark brown solid. Solids were rinsed with IPA and filtered to provide 2.58 g PBBN material (light brown in color and free flowing) upon drying (~57% yield), mp = 178.6 & 179.5 °C. Purity of the crude PBBN was found to be ~70% (trimethylbenzene as internal standard) and was used without further purification. The trace unreacted sodium cyanide was destroyed by bleach solution in the aqueous DMSO solution.

Preparation of PBPEA (9263–189): (Fig. 3) To a 3-neck, 100-ml RBF, fitted with a reflux condenser, thermocouple, and nitrogen inlet was charged absolute ethanol (30 g). Concentrated sulfuric acid (30 g) as added slowly as to minimize exotherm. When heating subsided, the starting nitrile, PBBN (1.0 g), was added in one portion. The temperature was set to ~96 °C, and the contents were allowed to reflux for 7 h. After heating for ~15 minutes, the reaction turned dark brown in color with no visible evidence of insoluble PBBN. After 2 h. heating, reflux had stabilized. Gradually, the temperature dropped to ~88 °C. The reactor was cooled, and the contents were poured into ice water. Immediately, a grey-brown solid precipitate was formed and subsequently collected via suction filtration. Air-drying overnight provided 1.65 grams crude material. The solids were slurried in acetone and filtered to collect 0.46 grams (42.2% yield) brown solid on drying. Crude NMR revealed desired ethyl ester as the major component. ¹H NMR: (400 MHz, DMSO-d6): δ = 4.32 (singlet, benzylic –CH₂–, 2H), 4.17–4.12 (quartet, ester methylene, 2H), 1.22–1.19 (triplet, ester methyl, 3H). (Impurities consist of the acetic acid derivative, along with the amide intermediate.) Recrystallization from acetone / IPA afforded the title ester compound obtained in pure form as spear-like needles, mp (DSC-melt) = 142.9–145.8 °C.