Acta Crystallographica Section E: Crystallographic Communications

Acta Crystallogr E Crystallogr Commun. 72(Pt 11): 1645-1647

Crystal structure of 1,2-bis(6-bromo-3,4-dihydro-2H-benz[e][1,3]oxazin-3-yl)ethane: a bromine-containing bis-benzoxazine

Augusto Riveraa*, Jicli José’ Rojasa, Jaime Ríos-Mottaa, Michael Bolteb

a. Universidad Nacional de Colombia, Sede Bogotá, Facultad de Ciencias, Departamento de Química, Cra 30 No. 45-03, Bogotá, Código Postal 110911, Colombia

b. Institut für Anorganische Chemie, J. W. Goethe-Universität Frankfurt, Max-von Laue-Str., 7, 60438 Frankfurt/Main, Germany

Correspondence e-mail: ariverau@unal.edu.co

© Rivera et al. 2016

DOI: 10.1107/S2056989016016509

Published online: 25 October 2016

Abstract

The solid-state structure of a 4-bromobenzoxazine has been determined. The whole molecule of the title compound is generated by inversion symmetry. This is a potential benzoxazine monomer for the preparation of phenolic materials.

Abstract

The title benzoxazine molecule, C₁₈H₁₈Br₂N₂O₂, was prepared by a Mannich-type reaction of 4-bromophenol with ethane-1,2-diamine and formaldehyde. The title compound crystallizes in the monoclinic space group C2/c with a centre of inversion located at the mid-point of the C—C bond of the central CH₂CH₂ spacer. The oxazinic ring adopts a half-chair conformation. The structure is compared to those of other functionalized benzoxazines synthesized in our laboratory. In the crystal, weak C—H⋯Br and C—H⋯O hydrogen bonds stack the molecules along the b-axis direction.

Chemical context  

In a continuation of our work on the synthesis and characterization of bis-1,3-benzoxazines, we have studied some of the chemical properties and determined the crystal structure of the title compound. Benzoxazines form an important class of benzo-fused heterocycles with a wide spectrum of biological activities. They are also emerging as desirable phenolic resin precursors because benzoxazines can undergo ring opening without emitting volatile materials during the curing process. This leads to a final cured product with excellent properties (Pilato, 2010 ▸). Normally, the incorporation of bromine can increase the flame-retarding properties and reduce the flammability of polymers (Li, et al., 2010 ▸). Recently, we have investigated the crystal structures of analogous bifunctional benzoxazines namely 3,3′-(ethane-1,2-diyl)bis(6-substituted-3,4-dihydro-2H-1,3-benzoxazine) (Rivera et al., 2010 ▸, 2011 ▸, 2012a ▸,b ▸) that were prepared to investigate whether replacement of the substituents at the para position of the phenyl ring affects the electrophilic anomeric effect in the N–C–O sequence of the adjacent oxazine ring. In addition, as benzoxazine contains a tertiary nitrogen atom, the lone-pair electrons may play an important role in the interaction with guest molecules but there are no reports on the inclusion properties of polybenzoxazines (Chirachanchai et al., 2011 ▸). An X-ray structural study may therefore provide a better understanding of the ability of benzoxazines to act as novel host–guest compounds. In our opinion, the title compound also has potential applications in the production of new bromine-containing phenolic resins.

Structural commentary  

The asymmetric unit of the title compound (Fig. 1 ▸), C₁₈H₁₈Br₂N₂O₂, contains one half of the organic molecule, an inversion centre generates the other half of the molecule (symmetry operation: 1 − x, 1 − y, 1 − z). The six-membered oxazine heterocyclic ring adopts a half-chair conformation, with puckering parameters Q = 0.512 (2) Å, θ =129.6 (2)°, φ = 283.6 (3)°. This ring is analysed with respect to the plane formed by O1/C3/C4/C5, with deviations of the C2 and N1 atoms from this plane of 0.300 (6) and −0.320 (4) Å, respectively.

The C—C bond distances and angles of the aromatic rings were found to be normal. The C3—O1 bond length [1.372 (6) Å] is comparable with other previously reported C—O bond lengths for related structures [1.370 (10) and 1.388 (9) Å (Rivera et al., 2012a ▸) and 1.376 (1) Å (Rivera et al., 2011 ▸)], but is found to be shorter in the p-chloro derivative where C—O = 1.421 (2) Å (Rivera et al., 2010 ▸). Interestingly, the C2—N1 and C2—O1 distances, 1.450 (5) and 1.456 (6) Å, respectively, are significantly different from the corresponding distances in the p-chloro derivative [1.369 (2) and 1.529 (2) Å, respectively; Rivera et al., 2010 ▸]. Indeed, the values observed here are closer to those found in the analogous compound with no p-substituent on the aromatic ring (1.424 and 1.463 Å, respectively; Rivera et al., 2012a ▸). This may indicate that the presence of the electron-withdrawing bromine atom does not significantly affect the adjacent oxazinic ring.

Supramolecular features  

In the crystal, weak C5—H5B⋯Br1 hydrogen bonds (Table 1 ▸) lead to the formation of inversion dimers with (12) ring motifs. These combine with the inversion symmetry of the molecule to produce chains of molecules along the c axis. Additional weak C2—H2B⋯O1 hydrogen bonds link these chains, stacking molecules along the b-axis direction, Fig. 2 ▸.

Database survey  

A database search yielded four comparable structures, namely 3,3′-(ethane-1,2-diyl)bis(6-methyl-3,4-dihydro-2H-1,3-benzoxazine) (AXAKAM; Rivera et al., 2011 ▸), 3,3′-ethylenebis(3,4-dihydro-6-chloro-2H-1,3-benzoxazine), (NUQKAM; Rivera et al., 2010 ▸), 3,3′-(ethane-1,2-diyl)bis(6-methoxy-3,4-dihydro-2H-1,3-benzoxazine) monohydrate (QEDDOU; Rivera et al., 2012b ▸), 3,3′-(ethane-1,2-diyl)bis(3,4-dihydro-2H-1,3-benzoxazine) (SAGPUN; Rivera et al., 2012a ▸). The Cl-substituted compound (NUQKAM) and the title compound are isomorphous. However, AXAKAM and SAGOUN have different space groups and in QEDDOU a solvent water molecule is included in the crystal packing.

Synthesis and crystallization  

An aqueous solution of formaldehyde (1.5 mL, 20 mmol) was added dropwise to a mixture of ethane-1,2-diamine (0.34 ml, 5 mmol) and 4-bromophenol (1.73 g, 10 mmol) dissolved in dioxane (10 ml). The reaction mixture was stirred for 4 h at room temperature. Single crystals were obtained from this solution by slow evaporation of the solvent.

Refinement  

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All the H atoms were located in the difference electron-density map. C-bound H atoms were fixed geometrically (C—H = 0.95 or 0.99 Å) and refined using a riding-model approximation, with U iso(H) set to 1.2U eq of the parent atom.

Figure 1View larger versionFigure 1. The molecular structure of the title compound, Displacement ellipsoids are drawn at the 50% probability level. Atoms labelled with the suffix A are generated using the symmetry operator (1 − x, 1 − y, 1 − z).

Figure 2View larger versionFigure 2. Packing diagram for the title compound, viewed along the b axis, with hydrogen bonds drawn as dashed lines.

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

See full table Table 2. Experimental details

Supplementary Material

Open In Web Browser

Acknowledgments

We acknowledge the Dirección de Investigaciones, Sede Bogotá (DIB) de la Universidad Nacional de Colombia for financial support of this work (research project No. 28427). JJR is also grateful to COLCIENCIAS for his doctoral scholarship

supplementary crystallographic information

Crystal data

See full table

Data collection

See full table

Refinement

See full table

Special details

See full table

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²)

See full table

Atomic displacement parameters (Å²)

See full table

Geometric parameters (Å, º)

See full table

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

See full table

Symmetry codes: (ii) −x+1, y, −z+3/2; (iii) −x+3/2, y−1/2, −z+3/2.

Articles from Acta Crystallographica Section E: Crystallographic Communications are provided here courtesy of International Union of Crystallography

PMC Copyright Notice

The articles available from the PMC site are protected by copyright, even though access is free. Copyright is held by the respective authors or publishers who provide these articles to PMC. Users of PMC are responsible for complying with the terms and conditions defined by the copyright holder.

Users should assume that standard copyright protection applies to articles in PMC, unless an article contains an explicit license statement that gives a user additional reuse or redistribution rights. PMC does not allow automated/bulk downloading of articles that have standard copyright protection.

See the copyright notice on the PMC site, https://www.ncbi.nlm.nih.gov/pmc/about/copyright/, for further details and specific exceptions.

References

Chirachanchai, S., Phongtamrug, S. & Tashiro, K. (2011). Supramolecular Chemistry of Benzoxazines: From Simple, Selective, Effective, and Efficient Macrocyclization Pathways to Host-Guest Properties. In Handbook of Benzoxazine Resins, pp 331–352. Amsterdam: Elsevier.

Li, S., Huang, W., Liu, X., Yu, X. & Xiao, W. (2010). Polym. Adv. Technol. 21, 229–234.

Pilato, L. (2010). Resin Chemistry In Phenolic Resins: A Century of Progress, edited by L. Pilato, pp. 41–91. Berlin Heidelberg: Springer-Verlag.

Rivera, A., Camacho, J., Ríos-Motta, J., Fejfarová, K. & Dušek, M. (2012a). Acta Cryst. E68, o148.

Rivera, A., Camacho, J., Ríos-Motta, J., Kučeraková, M. & Dušek, M. (2012b). Acta Cryst. E68, o2734.

Rivera, A., Camacho, J., Ríos-Motta, J., Pojarová, M. & Dušek, M. (2011). Acta Cryst. E67, o2028.

Rivera, A., Rojas, J. J., Ríos-Motta, J., Dušek, M. & Fejfarová, K. (2010). Acta Cryst. E66, o1134.

Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122.

Sheldrick, G. M. (2015). Acta Cryst. C71, 3–8.

Stoe & Cie (2001). X-AREA and X-RED32. Stoe & Cie, Darmstadt, Germany.

[Back]

C₁₈H₁₈Br₂N₂O₂ | F(000) = 904
Mr = 454.16 | Dx = 1.777 Mg m⁻³
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å
a = 19.464 (2) Å | Cell parameters from 3703 reflections
b = 5.9444 (7) Å | θ = 3.6–26.0°
c = 17.2225 (19) Å | µ = 4.79 mm⁻¹
β = 121.557 (7)° | T = 173 K
V = 1698.0 (3) Å³ | Block, colourless
Z = 4 | 0.27 × 0.26 × 0.26 mm

[Back]

[Back]

STOE IPDS II two-circle diffractometer | 1391 reflections with I > 2σ(I)
Radiation source: Genix 3D IµS microfocus X-ray source | Rint = 0.078
ω scans | θmax = 25.6°, θmin = 3.6°
Absorption correction: multi-scan (X-Area; Stoe & Cie, 2001) | h = −20→23
Tmin = 0.905, Tmax = 1.000 | k = −7→7
3703 measured reflections | l = −20→20
1583 independent reflections |

[Back]

[Back]

Refinement on F² | Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full | H-atom parameters constrained
R[F² > 2σ(F²)] = 0.056 | w = 1/[σ²(Fo²) + (0.099P)²] where P = (Fo² + 2Fc²)/3
wR(F²) = 0.143 | (Δ/σ)max < 0.001
S = 1.07 | Δρmax = 1.40 e Å⁻³
1583 reflections | Δρmin = −1.92 e Å⁻³
110 parameters | Extinction correction: SHELXL-2014/7 (Sheldrick 2015), Fc*=kFc[1+0.001xFc²λ³/sin(2θ)]-1/4
0 restraints | Extinction coefficient: 0.0037 (8)

[Back]

[Back]

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

[Back]

[Back]

| x | y | z | Uiso*/Ueq |
Br1 | 0.60406 (3) | −0.02845 (9) | 0.93353 (3) | 0.0226 (3) |
O1 | 0.67962 (18) | 0.6369 (6) | 0.7231 (2) | 0.0176 (7) |
N1 | 0.6072 (2) | 0.4166 (7) | 0.5842 (2) | 0.0130 (8) |
C1 | 0.5323 (2) | 0.5473 (7) | 0.5467 (3) | 0.0141 (10) |
H1A | 0.5430 | 0.7067 | 0.5401 | 0.017* |
H1B | 0.5124 | 0.5406 | 0.5891 | 0.017* |
C2 | 0.6783 (3) | 0.5494 (8) | 0.6434 (3) | 0.0155 (10) |
H2A | 0.6811 | 0.6770 | 0.6082 | 0.019* |
H2B | 0.7268 | 0.4552 | 0.6639 | 0.019* |
C3 | 0.6620 (3) | 0.4788 (8) | 0.7681 (3) | 0.0141 (9) |
C4 | 0.6259 (2) | 0.2721 (8) | 0.7288 (3) | 0.0142 (9) |
C5 | 0.6091 (2) | 0.2158 (8) | 0.6343 (3) | 0.0140 (9) |
H5A | 0.6513 | 0.1123 | 0.6400 | 0.017* |
H5B | 0.5566 | 0.1372 | 0.5995 | 0.017* |
C6 | 0.6083 (2) | 0.1218 (8) | 0.7781 (3) | 0.0147 (9) |
H6 | 0.5841 | −0.0193 | 0.7526 | 0.018* |
C7 | 0.6265 (3) | 0.1804 (8) | 0.8655 (3) | 0.0164 (9) |
C8 | 0.6619 (3) | 0.3870 (9) | 0.9044 (3) | 0.0223 (10) |
H8 | 0.6741 | 0.4248 | 0.9639 | 0.027* |
C9 | 0.6787 (3) | 0.5348 (8) | 0.8552 (3) | 0.0192 (11) |
H9 | 0.7021 | 0.6768 | 0.8807 | 0.023* |

[Back]

[Back]

| U ¹¹ | U ²² | U ³³ | U ¹² | U ¹³ | U ²³
Br1 | 0.0261 (4) | 0.0229 (4) | 0.0255 (4) | 0.00128 (17) | 0.0181 (3) | 0.00527 (19)
O1 | 0.0161 (15) | 0.0160 (18) | 0.0166 (15) | −0.0043 (12) | 0.0058 (13) | −0.0018 (13)
N1 | 0.0078 (16) | 0.0135 (19) | 0.0148 (17) | 0.0005 (13) | 0.0039 (14) | 0.0003 (15)
C1 | 0.010 (2) | 0.013 (2) | 0.014 (2) | 0.0037 (16) | 0.0029 (19) | −0.0009 (18)
C2 | 0.012 (2) | 0.016 (2) | 0.019 (2) | −0.0051 (16) | 0.0081 (18) | −0.0034 (18)
C3 | 0.0114 (19) | 0.014 (2) | 0.014 (2) | 0.0000 (15) | 0.0047 (17) | 0.0021 (17)
C4 | 0.0093 (18) | 0.015 (2) | 0.014 (2) | 0.0023 (16) | 0.0030 (15) | 0.0016 (17)
C5 | 0.0105 (19) | 0.012 (2) | 0.016 (2) | 0.0009 (15) | 0.0039 (16) | −0.0021 (17)
C6 | 0.0098 (18) | 0.015 (2) | 0.018 (2) | 0.0015 (15) | 0.0062 (16) | 0.0022 (18)
C7 | 0.020 (2) | 0.014 (2) | 0.020 (2) | 0.0032 (16) | 0.0137 (18) | 0.0057 (18)
C8 | 0.028 (2) | 0.023 (3) | 0.017 (2) | −0.001 (2) | 0.0126 (19) | −0.0036 (19)
C9 | 0.023 (2) | 0.015 (2) | 0.019 (2) | −0.0003 (17) | 0.011 (2) | −0.0020 (18)

[Back]

[Back]

Br1—C7 | 1.909 (5) | C3—C4 | 1.402 (6)
O1—C3 | 1.372 (6) | C4—C6 | 1.393 (7)
O1—C2 | 1.455 (6) | C4—C5 | 1.519 (6)
N1—C2 | 1.450 (5) | C5—H5A | 0.9900
N1—C5 | 1.462 (6) | C5—H5B | 0.9900
N1—C1 | 1.470 (5) | C6—C7 | 1.397 (7)
C1—C1i | 1.538 (8) | C6—H6 | 0.9500
C1—H1A | 0.9900 | C7—C8 | 1.396 (7)
C1—H1B | 0.9900 | C8—C9 | 1.373 (8)
C2—H2A | 0.9900 | C8—H8 | 0.9500
C2—H2B | 0.9900 | C9—H9 | 0.9500
C3—C9 | 1.398 (7) |  |
C3—O1—C2 | 113.7 (4) | C6—C4—C5 | 121.9 (4)
C2—N1—C5 | 108.0 (3) | C3—C4—C5 | 118.9 (4)
C2—N1—C1 | 112.6 (4) | N1—C5—C4 | 112.2 (4)
C5—N1—C1 | 113.8 (3) | N1—C5—H5A | 109.2
N1—C1—C1i | 110.2 (4) | C4—C5—H5A | 109.2
N1—C1—H1A | 109.6 | N1—C5—H5B | 109.2
C1i—C1—H1A | 109.6 | C4—C5—H5B | 109.2
N1—C1—H1B | 109.6 | H5A—C5—H5B | 107.9
C1i—C1—H1B | 109.6 | C4—C6—C7 | 119.5 (4)
H1A—C1—H1B | 108.1 | C4—C6—H6 | 120.3
N1—C2—O1 | 113.4 (4) | C7—C6—H6 | 120.3
N1—C2—H2A | 108.9 | C8—C7—C6 | 121.3 (4)
O1—C2—H2A | 108.9 | C8—C7—Br1 | 119.4 (4)
N1—C2—H2B | 108.9 | C6—C7—Br1 | 119.2 (4)
O1—C2—H2B | 108.9 | C9—C8—C7 | 118.9 (4)
H2A—C2—H2B | 107.7 | C9—C8—H8 | 120.5
O1—C3—C9 | 117.2 (4) | C7—C8—H8 | 120.5
O1—C3—C4 | 122.5 (4) | C8—C9—C3 | 120.8 (5)
C9—C3—C4 | 120.3 (5) | C8—C9—H9 | 119.6
C6—C4—C3 | 119.2 (4) | C3—C9—H9 | 119.6
C2—N1—C1—C1i | 151.1 (5) | C1—N1—C5—C4 | −77.1 (4)
C5—N1—C1—C1i | −85.6 (6) | C6—C4—C5—N1 | 161.5 (4)
C5—N1—C2—O1 | −64.9 (5) | C3—C4—C5—N1 | −20.1 (5)
C1—N1—C2—O1 | 61.6 (5) | C3—C4—C6—C7 | 0.3 (6)
C3—O1—C2—N1 | 47.8 (5) | C5—C4—C6—C7 | 178.7 (4)
C2—O1—C3—C9 | 166.5 (4) | C4—C6—C7—C8 | 0.1 (7)
C2—O1—C3—C4 | −15.8 (5) | C4—C6—C7—Br1 | −178.8 (3)
O1—C3—C4—C6 | −178.7 (4) | C6—C7—C8—C9 | 0.2 (7)
C9—C3—C4—C6 | −1.1 (6) | Br1—C7—C8—C9 | 179.2 (4)
O1—C3—C4—C5 | 2.9 (6) | C7—C8—C9—C3 | −1.0 (7)
C9—C3—C4—C5 | −179.5 (4) | O1—C3—C9—C8 | 179.2 (4)
C2—N1—C5—C4 | 48.7 (5) | C4—C3—C9—C8 | 1.4 (7)

[Back]

[Back]

D—H···A | D—H | H···A | D···A | D—H···A
C5—H5B···Br1ii | 0.99 | 3.04 | 3.951 (5) | 154
C2—H2B···O1iii | 0.99 | 2.64 | 3.506 (6) | 146

[Back]

[Back]

Figure 1.

The molecular structure of the title compound, Displacement ellipsoids are drawn at the 50% probability level. Atoms labelled with the suffix A are generated using the symmetry operator (1 − x, 1 − y, 1 − z).

[Back]

[Back]

Figure 2.

Packing diagram for the title compound, viewed along the b axis, with hydrogen bonds drawn as dashed lines.

[Back]

[Back]

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

D—H⋯A | D—H | H⋯A | D⋯A | D—H⋯A
C5—H5B⋯Br1i | 0.99 | 3.04 | 3.951 (5) | 154
C2—H2B⋯O1ii | 0.99 | 2.64 | 3.506 (6) | 146

Symmetry codes: (i) ; (ii) .

[Back]

[Back]

Table 2. Experimental details

Crystal data
Chemical formula | C₁₈H₁₈Br₂N₂O₂
M r | 454.16
Crystal system, space group | Monoclinic, C2/c
Temperature (K) | 173
a, b, c (Å) | 19.464 (2), 5.9444 (7), 17.2225 (19)
β (°) | 121.557 (7)
V (Å³) | 1698.0 (3)
Z | 4
Radiation type | Mo Kα
μ (mm⁻¹) | 4.79
Crystal size (mm) | 0.27 × 0.26 × 0.26
Data collection
Diffractometer | STOE IPDS II two-circle
Absorption correction | Multi-scan (X-AREA; Stoe & Cie, 2001 ▸)
T min, T max | 0.905, 1.000
No. of measured, independent and observed [I > 2σ(I)] reflections | 3703, 1583, 1391
R int | 0.078
(sin θ/λ)max (Å⁻¹) | 0.607
Refinement
R[F ² > 2σ(F ²)], wR(F ²), S | 0.056, 0.143, 1.07
No. of reflections | 1583
No. of parameters | 110
H-atom treatment | H-atom parameters constrained
Δρmax, Δρmin (e Å⁻³) | 1.40, −1.92

Computer programs: X-AREA (Stoe & Cie, 2001 ▸), SHELXS (Sheldrick, 2008 ▸), SHELXL2014/7 (Sheldrick, 2015 ▸) and XP in SHELXTL-Plus (Sheldrick, 2008 ▸).

[Back]