research communications
2,6-Dibromo-3,4,5-trimethoxybenzoic acid
aFaculty of Chemistry and Pharmacy, University of Regensburg, Universitaetsstr. 31, 93053 Regensburg, Germany, and bFaculty of Pharmacy, Department of Pharmaceutical Chemistry, Medical University "Prof. Dr. Paraskev Stoyanov" Varna, 84 "Tzar Osvoboditel" Blvd., 9000 Varna, Bulgaria
*Correspondence e-mail: michael.bodensteiner@ur.de, ilian.kolev@mu-varna.bg
The title compound, 2,6-dibromo-3,4,5-trimethoxybenzoic acid (DBrTMBA), C10H10Br2O5, was obtained by bromination and transhalogenation of 2-iodo-3,4,5-trimethoxybenzoic acid with KBrO3. Like the previously reported 2,6-diiodo-3,4,5-trimethoxybenzoic acid (DITMBA), the structure of the title compound features a catemeric arrangement of DBrTMBA molecules along an endless chain of carboxylic H–carbonyl interactions. A short carbonyl–phenyl contact hints at a possible lone pair(O)–π-hole interaction further stabilizing the chain-like structure over a dimeric arrangement of the carboxylic acid.
Keywords: crystal structure; Hirshfeld atom refinement (HAR); NoSpherA2; substituted trimethoxybenzoic acid.
CCDC reference: 2281408
1. Chemical context
Organobromine compounds are valuable precursors in organic and pharmaceutical synthesis. Their participation in homo- and cross-coupling reactions is undisputed and even preferred over the other halogen-containing compounds. In practice, many brominating agents are used for their synthesis, though few of them appear to be safe both for the user-chemist and environment. Therefore, in the present work, we present a new environmentally friendly method for the synthesis of 2,6-dibromo-3,4,5-trimethoxybenzoic acid. Its structure is closely related to those of mono- and diiodo-3,4,5-trimethoxybenzoic acids ITMBA and DITMBA (Kolev et al., 2021, 2023).
2. Structural commentary
DBrTMBA (Fig. 1) crystallizes in the monoclinic P21/n with one acid molecule in the (Z = 4). The carboxylic acid (O1/C7/O2) group is almost perpendicular to the geometrical C6 mean plane and at an angle of 86.7 (2)°. This derivation is exactly in the middle of the reported geometries of the catemeric DITMBA, which is closer to 90° and the reported dimeric DITMBA·toluene, which deviates more from 90° (Kolev et al., 2023).
3. Supramolecular features
Different to the also related structures of mono- and diiodo-3,4,5-trimethoxybenzoic acids ITMBA and DITMBA·toluene (Kolev et al., 2021, 2023), the title compound exhibits no dimeric structure in the solid state (Fig. 2). Instead, a hydrogen-bonded chain along the crystallographic b-axis direction between neighbouring acids is observed. Molecules of DBrTMBA are arranged in a catemeric fashion along this chain of carboxylic hydrogen interaction. The structure is thus very similar to that of solvent-free DITMBA (Kolev et al., 2023). The O1—O2 distance of the DBrTMBA intermolecular hydrogen-bonding interaction is 2.617 (5) Å (Table 1, Fig. 3).
Another interesting structural feature in this syndiotactic arrangement can be described as a carbonyl O2 lone pair(lp)–π (C6) contact with a distance from O2 to the center of geometry of the benzene ring of 3.030 (4) Å (Fig. 2). This contact presumably contributes to the deviation from the dimeric structure as observed in ITMBA and DITMBA· toluene (Kolev et al., 2021, 2023). In the latter, the toluene solvent molecule seems to shield the C6 π system from this kind of interaction, giving rise to a preferred dimeric structure in this solvate.
To understand the crystal packing of DBrTMBA and the contribution of these closest interaction contacts, the software program CrystalExplorer was used for a Hirshfeld surface and interaction analysis (Spackman et al., 2021). Fig. 4b–d show the closest contacts of the hydroxylic acid group as donor/acceptor in hydrogen bonding, as well as the O(lp)–π (C6) interaction in Fig. 4f. The hydrogen donor/acceptor properties of the carboxylic group are visualized in the mapping of the electrostatic potential at the Hirshfeld surface (Fig. 4e).
Table 2 shows the interaction energies of DBrTMBA with the closest neighbor molecules in the crystal packing (colors in Fig. 4g). As expected, the strongest intermolecular interaction is exhibited over the carboxylic hydrogen contacts as well as the O(lp)–π (C6) interaction (purple-coloured neighbors).
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The fingerprint plots (Fig. 5) show the various contributions of Br⋯H, O⋯H, H⋯H and C⋯H interactions to the Hirshfeld surface, indicating a high contribution of Br⋯H and O⋯H interactions.
4. Database survey
Five crystal structures from other authors featuring 3,4,5-trimethoxybenzoic acid (TMBA) are known in the Cambridge Structural Database (CSD, WebCSD search July 2023; Groom et al., 2016). The structure of the parent compound, which crystallizes in Pc, has been reported twice (Qadeer et al., 2007, Bolte, 2011). Three other structures contain TMBA co-crystallized with other organic molecules (Thomas et al., 2019; Chen et al., 2018; Zhang et al., 2021). All of them reveal co-planar arrangements of the benzene rings and hydrogen-bonding interactions. Furthermore, we recently reported on the previously discussed mono- and diiodo-3,4,5-trimethoxybenzoic acids ITMBA and DITMBA (Kolev et al., 2021, 2023).
5. Synthesis and crystallization
The title compound was synthesized according to the following experimental procedure: A solution of 2-iodo-3,4,5-trimethoxybenzoic acid (0.36 mmol) in 0.2 M NaOH (0.5 mL) was added dropwise to a magnetically stirred aqueous sulfuric acid solution (3.2 M, 0.6 mL) of KBrO3 (0.72 mmol). The temperature of the reaction mixture was then raised gradually from 294 to 338 K. The resulting solution was stirred for an additional 4.0 h at 338 K and then allowed to cool slowly down (without stirring) to room temperature. The desired product, 2,6-dibromo-3,4,5-trimethoxybenzoic acid, crystallized as long, thin needles (m.p. 417–421 K; yield: 30%).
6. Refinement
Crystal data, data collection and structure . An Hirshfeld Atom (HAR) using NoSpherA2 in Olex2 was performed to obtain non-spherical atomic form factors as well as anisotropic hydrogen atomic displacement parameters (Hirshfeld, 1977, Kleemiss et al., 2021). Orca5 (Neese et al., 2020) was used for the single-point calculations for the HAR procedure at def2-TZVP/M062X level of theory. The H—X distances were fixed to neutron distances from Allen & Bruno (2010) and refined anisotropically with displacement parameter restraints. The choice to fix the H—X distances to neutron distances was made because, even after several attempts at data collection, the data from DBrTMBA did not allow for the of unrestrained hydrogen distances, but did allow for the of softly restrained hydrogen atom anisotropic displacement parameters at these fixed distances.
details are summarized in Table 3Supporting information
CCDC reference: 2281408
https://doi.org/10.1107/S2056989023007831/jy2033sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989023007831/jy2033Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989023007831/jy2033Isup3.cml
Data collection: CrysAlis PRO 1.171.43.36a (Rigaku OD, 2022); cell
CrysAlis PRO 1.171.43.36a (Rigaku OD, 2022); data reduction: CrysAlis PRO 1.171.43.36a (Rigaku OD, 2022); program(s) used to solve structure: SHELXT2018/2 (Sheldrick, 2015); program(s) used to refine structure: olex2.refine 1.5-alpha (Bourhis et al., 2015), NoSpherA2 (Kleemiss et al., 2021); molecular graphics: Olex2 1.5-alpha (Dolomanov et al., 2009); software used to prepare material for publication: publCIF (Westrip, 2010).C10H10Br2O5 | F(000) = 718.856 |
Mr = 370.00 | Dx = 1.875 Mg m−3 |
Monoclinic, P21/n | Mo Kα radiation, λ = 0.71073 Å |
a = 11.4047 (9) Å | Cell parameters from 1911 reflections |
b = 7.1107 (3) Å | θ = 3.1–28.8° |
c = 16.8997 (13) Å | µ = 6.19 mm−1 |
β = 107.009 (8)° | T = 100 K |
V = 1310.54 (16) Å3 | Block, clear colourless |
Z = 4 | 0.08 × 0.06 × 0.03 mm |
SuperNova, Dualflex, AtlasS2 diffractometer | 3245 independent reflections |
Radiation source: micro-focus sealed X-ray tube, SuperNova (Mo) X-ray Source | 2254 reflections with I ≥ 2u(I) |
Mirror monochromator | Rint = 0.084 |
Detector resolution: 5.2548 pixels mm-1 | θmax = 28.3°, θmin = 3.1° |
ω scans | h = −17→19 |
Absorption correction: gaussian (CrysAlisPro; Rigaku OD, 2022) | k = −12→6 |
Tmin = 0.749, Tmax = 0.855 | l = −28→28 |
18764 measured reflections |
Refinement on F2 | 4 constraints |
Least-squares matrix: full | Primary atom site location: dual |
R[F2 > 2σ(F2)] = 0.053 | Only H-atom displacement parameters refined |
wR(F2) = 0.123 | w = 1/[σ2(Fo2) + (0.0395P)2 + 3.4625P] where P = (Fo2 + 2Fc2)/3 |
S = 1.06 | (Δ/σ)max = 0.0002 |
3245 reflections | Δρmax = 1.25 e Å−3 |
218 parameters | Δρmin = −1.48 e Å−3 |
63 restraints |
x | y | z | Uiso*/Ueq | ||
Br1 | 0.86638 (5) | 0.67372 (7) | 0.45104 (4) | 0.03398 (18) | |
Br2 | 0.43161 (5) | 0.68854 (7) | 0.17096 (3) | 0.03341 (18) | |
O1 | 0.6558 (4) | 0.9831 (5) | 0.3032 (2) | 0.0315 (9) | |
H1 | 0.692 (6) | 1.0810 (6) | 0.277 (4) | 0.04 (2) | |
O2 | 0.7570 (4) | 0.7934 (5) | 0.2410 (3) | 0.0384 (11) | |
O3 | 0.7246 (5) | 0.3480 (5) | 0.5004 (3) | 0.0468 (12) | |
O4 | 0.5037 (4) | 0.1913 (5) | 0.4131 (3) | 0.0442 (12) | |
O5 | 0.3643 (4) | 0.3576 (5) | 0.2669 (3) | 0.0484 (13) | |
C4 | 0.6357 (4) | 0.6586 (6) | 0.3198 (3) | 0.0200 (10) | |
C5 | 0.7054 (5) | 0.5773 (7) | 0.3932 (3) | 0.0278 (12) | |
C3 | 0.5234 (5) | 0.5822 (7) | 0.2773 (4) | 0.0284 (12) | |
C6 | 0.6606 (6) | 0.4204 (7) | 0.4262 (3) | 0.0312 (13) | |
C2 | 0.4771 (5) | 0.4239 (7) | 0.3079 (4) | 0.0319 (13) | |
C7 | 0.6884 (5) | 0.8184 (7) | 0.2838 (3) | 0.0261 (12) | |
C1 | 0.5451 (6) | 0.3442 (7) | 0.3827 (4) | 0.0300 (13) | |
C8 | 0.7911 (7) | 0.1815 (8) | 0.4937 (4) | 0.0472 (17) | |
H00a | 0.852 (3) | 0.2105 (16) | 0.457 (2) | 0.056 (11) | |
H00b | 0.844 (3) | 0.136 (3) | 0.5545 (5) | 0.057 (10) | |
H00c | 0.7277 (7) | 0.0722 (18) | 0.465 (2) | 0.048 (10) | |
C10 | 0.3618 (7) | 0.1753 (8) | 0.2314 (5) | 0.0523 (19) | |
H00d | 0.2696 (10) | 0.142 (3) | 0.195 (2) | 0.066 (11) | |
H00e | 0.421 (3) | 0.173 (2) | 0.192 (2) | 0.061 (11) | |
H00f | 0.393 (4) | 0.0726 (11) | 0.2799 (5) | 0.060 (11) | |
C9 | 0.4330 (7) | 0.2341 (9) | 0.4679 (5) | 0.056 (2) | |
H00g | 0.359 (2) | 0.326 (5) | 0.4373 (10) | 0.062 (10) | |
H00h | 0.397 (3) | 0.1060 (11) | 0.485 (2) | 0.052 (10) | |
H00i | 0.4904 (11) | 0.302 (5) | 0.5224 (12) | 0.072 (11) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Br1 | 0.0308 (3) | 0.0207 (3) | 0.0382 (4) | 0.0033 (2) | −0.0091 (2) | −0.0047 (2) |
Br2 | 0.0382 (4) | 0.0181 (3) | 0.0312 (3) | 0.0032 (2) | −0.0097 (2) | −0.0045 (2) |
O1 | 0.043 (2) | 0.0208 (19) | 0.038 (2) | −0.0014 (17) | 0.0242 (19) | 0.0003 (16) |
H1 | 0.08 (4) | 0.03 (3) | 0.04 (3) | −0.024 (13) | 0.033 (17) | −0.006 (13) |
O2 | 0.061 (3) | 0.0176 (19) | 0.056 (3) | 0.0006 (18) | 0.047 (2) | 0.0001 (18) |
O3 | 0.083 (4) | 0.029 (2) | 0.031 (2) | 0.010 (2) | 0.021 (2) | 0.0072 (18) |
O4 | 0.068 (3) | 0.021 (2) | 0.062 (3) | 0.0039 (19) | 0.048 (3) | 0.0028 (19) |
O5 | 0.027 (2) | 0.026 (2) | 0.089 (4) | −0.0041 (17) | 0.013 (2) | −0.007 (2) |
C4 | 0.023 (3) | 0.015 (2) | 0.025 (3) | −0.0035 (19) | 0.012 (2) | −0.0007 (18) |
C5 | 0.035 (3) | 0.022 (3) | 0.028 (3) | 0.004 (2) | 0.012 (2) | 0.000 (2) |
C3 | 0.026 (3) | 0.019 (3) | 0.040 (3) | −0.002 (2) | 0.009 (2) | −0.002 (2) |
C6 | 0.049 (4) | 0.020 (3) | 0.028 (3) | 0.002 (2) | 0.018 (3) | 0.004 (2) |
C2 | 0.026 (3) | 0.024 (3) | 0.050 (4) | −0.005 (2) | 0.016 (3) | −0.001 (2) |
C7 | 0.036 (3) | 0.014 (2) | 0.035 (3) | 0.003 (2) | 0.022 (2) | −0.001 (2) |
C1 | 0.043 (3) | 0.015 (2) | 0.040 (3) | −0.001 (2) | 0.026 (3) | 0.003 (2) |
C8 | 0.068 (5) | 0.028 (3) | 0.039 (4) | 0.009 (3) | 0.006 (3) | 0.008 (3) |
H00a | 0.069 (13) | 0.05 (3) | 0.041 (11) | 0.005 (8) | 0.006 (6) | 0.012 (7) |
H00b | 0.072 (15) | 0.05 (2) | 0.042 (7) | 0.006 (8) | 0.005 (5) | 0.014 (5) |
H00c | 0.066 (17) | 0.031 (15) | 0.040 (12) | 0.011 (8) | 0.008 (6) | 0.008 (6) |
C10 | 0.050 (5) | 0.028 (3) | 0.077 (6) | −0.005 (3) | 0.016 (4) | −0.009 (3) |
H00d | 0.054 (7) | 0.06 (3) | 0.082 (14) | −0.012 (5) | 0.015 (5) | −0.003 (8) |
H00e | 0.053 (10) | 0.05 (3) | 0.078 (13) | −0.008 (7) | 0.016 (6) | −0.010 (8) |
H00f | 0.063 (13) | 0.036 (19) | 0.079 (14) | −0.003 (7) | 0.018 (6) | −0.007 (8) |
C9 | 0.076 (6) | 0.036 (4) | 0.081 (6) | 0.010 (3) | 0.063 (5) | 0.010 (4) |
H00g | 0.082 (12) | 0.038 (11) | 0.09 (2) | 0.012 (5) | 0.059 (8) | 0.008 (6) |
H00h | 0.081 (17) | 0.033 (9) | 0.073 (19) | 0.012 (6) | 0.070 (8) | 0.003 (6) |
H00i | 0.10 (2) | 0.041 (12) | 0.092 (12) | 0.008 (6) | 0.051 (8) | 0.007 (6) |
Br1—C5 | 1.935 (6) | C5—C6 | 1.408 (7) |
Br2—C3 | 1.948 (6) | C3—C2 | 1.405 (7) |
O1—C7 | 1.299 (6) | C6—C1 | 1.415 (8) |
O2—C7 | 1.224 (6) | C2—C1 | 1.395 (8) |
O3—C6 | 1.354 (7) | C8—H00a | 1.0770 |
O3—C8 | 1.429 (7) | C8—H00b | 1.0770 |
O4—C1 | 1.346 (6) | C8—H00c | 1.0770 |
O4—C9 | 1.427 (7) | C10—H00d | 1.0770 |
O5—C2 | 1.355 (7) | C10—H00e | 1.0770 |
O5—C10 | 1.425 (7) | C10—H00f | 1.0770 |
C4—C5 | 1.388 (7) | C9—H00g | 1.0770 |
C4—C3 | 1.383 (7) | C9—H00h | 1.0770 |
C4—C7 | 1.496 (7) | C9—H00i | 1.0770 |
C1—C2—C3 | 119.3 (5) | C8—O3—C6 | 113.4 (5) |
C1—C2—O5 | 121.0 (5) | C9—O4—C1 | 113.8 (4) |
C1—C6—C5 | 119.2 (5) | H00a—C8—O3 | 109.5 |
C1—C6—O3 | 120.2 (5) | H00b—C8—H00a | 109.5 |
C10—O5—C2 | 115.5 (5) | H00b—C8—O3 | 109.5 |
C2—C1—C6 | 120.1 (5) | H00c—C8—H00b | 109.5 |
C2—C1—O4 | 120.6 (6) | H00c—C8—H00a | 109.5 |
C2—C3—C4 | 120.9 (5) | H00c—C8—O3 | 109.5 |
C2—C3—Br2 | 119.5 (4) | H00d—C10—O5 | 109.5 |
C3—C2—O5 | 119.6 (5) | H00e—C10—H00d | 109.5 |
C3—C4—C5 | 120.1 (5) | H00e—C10—O5 | 109.5 |
C4—C7—O2 | 122.1 (4) | H00f—C10—H00e | 109.5 |
C4—C7—O1 | 113.8 (4) | H00f—C10—H00d | 109.5 |
C4—C3—Br2 | 119.5 (4) | H00f—C10—O5 | 109.5 |
C4—C5—Br1 | 121.0 (4) | H00g—C9—O4 | 109.5 |
C5—C6—O3 | 120.5 (6) | H00h—C9—H00g | 109.5 |
C6—C1—O4 | 119.3 (5) | H00h—C9—O4 | 109.5 |
C6—C5—C4 | 120.3 (5) | H00i—C9—H00h | 109.5 |
C6—C5—Br1 | 118.8 (4) | H00i—C9—H00g | 109.5 |
C7—C4—C3 | 120.5 (5) | H00i—C9—O4 | 109.5 |
C7—C4—C5 | 119.1 (5) | O2—C7—O1 | 124.0 (5) |
C7—O1—H1 | 109.5 | ||
Br1—C5—C4—C3 | 176.9 (4) | O3—C6—C5—C4 | −175.7 (5) |
Br1—C5—C4—C7 | 2.2 (5) | O3—C6—C1—O4 | −4.6 (6) |
Br1—C5—C6—O3 | 5.3 (5) | O3—C6—C1—C2 | 177.3 (5) |
Br1—C5—C6—C1 | −177.5 (4) | O4—C1—C6—C5 | 178.3 (5) |
Br2—C3—C4—C5 | −176.2 (4) | O4—C1—C2—O5 | 4.4 (6) |
Br2—C3—C4—C7 | −1.7 (5) | O4—C1—C2—C3 | −179.2 (5) |
Br2—C3—C2—O5 | −5.8 (5) | O5—C2—C3—C4 | 176.9 (5) |
Br2—C3—C2—C1 | 177.8 (4) | O5—C2—C1—C6 | −177.5 (5) |
O1—C7—C4—C5 | −96.1 (5) | C4—C5—C6—C1 | 1.4 (6) |
O1—C7—C4—C3 | 89.3 (5) | C4—C3—C2—C1 | 0.5 (6) |
O2—C7—C4—C5 | 83.0 (6) | C5—C6—C1—C2 | 0.2 (6) |
O2—C7—C4—C3 | −91.5 (6) | C3—C2—C1—C6 | −1.2 (6) |
D—H···A | D—H | H···A | D···A | D—H···A |
O1—H1···O2i | 0.98 (5) | 1.68 (3) | 2.617 (5) | 160 (5) |
Symmetry code: (i) −x+3/2, y+1/2, −z+1/2. |
Values calculated with CrystalExplorer at the B3LYP/6-31G(d,p) level of theory. el: electrostatic, pol: polarization, disp: dispersion, rep: repulsion. |
Color code | Symmetry operation | Eel | Epol | Edisp | Erep | Etotal |
Red | -x + 1/2, y + 1/2, -z + 1/2 | -1.1 | -1.0 | -14.0 | 6.1 | -10.3 |
Orange | x + 1/2, -y + 1/2, z + 1/2 | -5.6 | -0.7 | -10.7 | 8.3 | -10.7 |
Light green | x, y, z | -6.3 | -1.5 | -25.8 | 16.2 | -20.2 |
Green | -x, -y, -z | -3.1 | -0.8 | -17.3 | 12.9 | -11.0 |
Cyan | x + 1/2, -y + 1/2, z + 1/2 | -3.3 | -0.3 | -7.3 | 8.7 | -4.7 |
Blue | -x, -y, -z | -9.0 | -2.0 | 37.6 | 22.1 | -30.1 |
Purple | -x + 1/2, y + 1/2, -z + 1/2 | -63.4 | -17.1 | -28.1 | 80.0 | -54.7 |
Pink | -x, -y, -z | -1.8 | -0.4 | -13.8 | 11.4 | -7.1 |
Funding information
Funding for this research was provided by the Institutional grant program of Medical University "Prof. Dr. Paraskev Stoyanov", Varna, "Nauka" (Project 20023).
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