1,2,4,5-Tetrabromobenzene

1,2,4,5-Tetrabromobenzene is an organobromine compound with the formula C6H2Br4. It is one of three isomers of tetrabromobenzene. The compound is a white solid. 1,2,4,5-Tetrabromobenzene is an important metabolite of the flame retardant hexabromobenzene.[1]

1,2,4,5-Tetrabromobenzene
Identifiers
3D model (JSmol)
ECHA InfoCard 100.010.231
EC Number
  • 211-253-3
UNII
Properties
C6H2Br4
Appearance white solid
Density 2.518 g/cm3
Melting point 180–182 °C (356–360 °F; 453–455 K)
Hazards
GHS pictograms
GHS Signal word Warning
GHS hazard statements
 H315, H319, H335, H413
P261, P264, P271, P273, P280, P302+352, P304+340, P305+351+338, P312, P321, P332+313, P337+313, P362, P403+233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Preparation

The synthesis of 1,2,4,5-tetrabromobenzene has already been reported in 1865 from benzene and excess bromine in a sealed tube at 150 °C.[2] However, the clearly reduced melting point of about 160 °C indicates impurities in the final product. In his 1885 dissertation, Adolf Scheufelen published the synthesis of a purer sample using iron(III) chloride FeCl3 as a catalyst, isolated as "pretty needles" ("schönen Nadeln").[3]

Synthese von 1,2,4,5-Tetrabrombenzol

The synthesis can also be carried out in solution in chloroform or tetrachloromethane and yields 1,2,4,5-tetrabromobenzene in 89% yield.[4] This reaction can also be carried out in a laboratory experiment with excess bromine and iron nails (as starting material for iron (III) bromide FeBr3).[5] The intermediate stage is 1,4-dibromobenzene, which reacts further with excess bromine to give 1,2,4,5-tetrabromobenzene.

Reactions

Building block for liquid crystals and fluorescent dyes

Owing to its symmetrical structure and reactivity, 1,2,4,5-tetrabromobenzene is a precursor to nematic liquid crystals[6] with crossed mesogens and for columnar (discotic) liquid crystals[7][8] with an extensive planar, "board-like" tetrabenzoanthracene core.

Synthesis of discotic LC from 1,2,4,5-Tetrabromobenzene.

In a one-pot reaction, 1,2,4,5-tetrabromobenzene reacts with 4-hydroxybenzaldehyde, the alkylating agent 1-bromopentane, the Wittig reagent methyltriphenylphosphonium iodide, the base potassium carbonate, the phase transfer catalyst tetrabutylammonium bromide, the Heck reagent palladium(II)acetate and the Heck co-catalyst 1,3-bis(diphenylphosphino)propane (dppp) in dimethylacetamide obtaining directly a symmetrical tetraalkoxylstilbene as E-isomer in 17% yield.[9]

Synthese eines symmetrischer Tetraalkoxystilbens

Due to their pronounced π-conjugation such compounds could be potentially applied as optical brighteners, OLED materials or liquid crystals.

N-alkyl-tetraaminobenzenes are available from 1,2,4,5-tetrabromobenzene in high yields, which can be cyclized with triethyl orthoformate and acids to benzobis(imidazolium) salts (BBI salts) and oxidized with oxygen to form 1,4-benzoquinone diimines.[10]

Synthese von BBI-Salzen und Benzochinondiiminen

BBI salts are versatile fluorescent dyes with emission wavelengths λem between 329 and 561 nm, pronounced solvatochromism and strong solvent-dependent Stokes shift, which can be used as protein tag for fluorescent labeling of proteins.[11]

Starting material for arynes

From 1,2,4,5-tetrabromobenzene, a 1,4-monoarine can be prepared in-situ with one equivalent of n-butyllithium by bromine abstraction, which reacts immediately with furan to form 6,7-dibromo-1,4-epoxy-1,4-dihydronaphthalene (6,7-dibromonaphthalene-1,4-endoxide) in 70% yield.[12]

Bildung eines 1,4-Monoarins aus 1,2,4,5-Tetrabrombenzol

When 2,5-dialkylfurans (e.g. 2,5- (di-n-octyl)furan) are used, the dibrominated monoendoxide is formed in 64% yield, from which dibromo-5,8-di-n-octylnaphthalene is formed with zink powder/titanium tetrachloride in 88% yield.[13]

Synthese von Dibromdioctylnaphthalin aus 1,2,4,5-Tetrabrombenzol

Upon treatment with titanium tetrachloride and zinc dust, the endoxide is deoxygenated yielding 2,3-dibromnaphthalene.[14]

The endoxide reacts with 3-sulfolene in a Diels-Alder reaction upon elimination of sulfur dioxide. The resulting tricyclic adduct converts to 2,3-dibromoanthracene in good yield.[15]

If the dibromene oxide is allowed to react further with furan, in the presence of n-butyllithium[12] or potassium amide[16] or via an intermediate 1,4-aryne the tricyclic 1,4-adduct 1,4:5.8-diepoxy-1,4,5,8-tetrahydroanthracene[17] is formed in 71% yield as a syn-anti-mixture. With sodium amide in ethylene glycol dimethyl ether (DME), however, the dibromene oxide behaves as a 1,3-aryne equivalent and forms with furan a phenanthrene-like tricyclic 1,3-adduct, which can react with furan and sodium amide to a triphenylene derivative (1,3,5-tris-arene).[16]

[2+4] cycloadditions with 1,2,4,5-tetrabromobenzene sometimes proceed in very high yields, such as the reaction of a dihalogen-substituted 1,3-diphenyl-isobenzofuran to a tetrahalogenated anthracene derivative (98%), which is converted successively further with 1,3-diphenyl isobenzofuran in 65% yield to a pentacene derivative and furan to a hexacene derivative (67%).[18]

Bildung eines Hexacen-Derivats aus 1,2,4,5-Tetrabrombenzol

The crosslinking of benzimidazole-modified polymers provides materials with a high absorption capacity for carbon dioxide, which could be suitable for CO2 separation from gas mixtures.[19]

Bildung eines vernetzten Benzimidazolpolymers

It is the starting material for mono- and bis-aryines.[12]

Safety

1,2,4,5-Tetrabromobenzene is a liver toxic degradation product of the flame retardant hexabromobenzene and was already in 1987 detected in Japan in mother's milk samples.[20]

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gollark: Everything but the CPU/cooler/RAM probably.
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References
  1. E. Bruchajzer; B. Frydrych; J.A. Szymanska (2004), "Effect of repeated administration of hexabromobenzene and 1,2,4,5-tetrabromobenzene on the levels of selected cytochromes in rat liver", Int. J. Occup. Med. Environ. Health, 17 (3), pp. 347–353, doi:10.1016/S0040-4020(01)87581-5
  2. A. Riche, P. Bérard (1865), "Ueber die bromhaltigen Derivate des Benzols und seiner Homologen" (PDF), Liebigs Ann. Chem. (in German), 133 (1), pp. 51–54, doi:10.1002/jlac.18651330106
  3. A. Scheufelen (1885), "Ueber Eisenverbindungen als Bromüberträger", Liebigs Ann. Chem. (in German), 231 (2), pp. 152–195, doi:10.1002/jlac.18852310204
  4. US 0
  5. B. Cox; D.G. Kubler; C.A. Wilson (1977), "Experiments with electrophilic aromatic substitution reactions", J. Chem. Educ., 54 (6), p. 379, doi:10.1021/ed054p379
  6. H.-H. Chen; et al. (2012), "Enantiotropic nematics from cross-like 1,2,4,5-tetrakis(4'-alkyl-4-ethynylbiphenyl) benzenes and their biaxiality studies", Chem. Eur. J., 18 (31), pp. 9543–9551, doi:10.1002/chem.201103453
  7. S. Kumar (2011), Chemistry of discotic liquid crystals: from monomers to polymers, Boca Raton, FL, U.S.A.: CRC Press, p. 200, ISBN 978-1-4398-1145-0
  8. M.C. Artal; K.J. Toyne; J.W. Goodby; J. Barbera; D.J. Photinos (2011), "Synthesis and mesogenic properties of novel board-like liquid crystals", J. Mater. Chem., 11, pp. 2801–2807, doi:10.1039/B105351P
  9. K.N. Patel; B.V. Kamath; A.V. Bedekar (2013), "Synthesis of alkyloxy stilbenes by one-pot O-alkylation-Wittig and O-alkylation-Wittig-Heck reaction sequence", Tetrahedron Lett., 54 (1), pp. 80–84, doi:10.1016/j.tetlet.2012.10.102
  10. D.M. Khramov; A.J. Boydston; C.W. Bielawski (2006), "Highly efficient synthesis and solid-state characterization of 1,2,4,5-tetrakis(alkyl- and arylamino)benzenes and cyclization to their respective benzobis(imidazolium) salts", Org. Lett., 8 (9), pp. 1831–1834, doi:10.1021/ol060349c
  11. A.J. Boydston (2008), "Modular fluorescent benzobis(imidazolium)saltes: Syntheses, photophysical analyses, and applications", J. Am. Chem. Soc., 130 (10), pp. 3143–3156, doi:10.1021/ja7102247
  12. K. Shahlai; S. O. Acquaah; H. Hart (1998). "USE OF 1,2,4,5-Tetrabromobenzene as a 1,4-Benzadiyne Equivalent: Anti- and Syn-1,4,5,8-Tetrahydroanthracene 1,4:5,8-Diepoxide". Organic Syntheses. 75: 201. doi:10.15227/orgsyn.075.0201.
  13. Z. Chen; P. Müller; T.M. Swager (2006), "Syntheses of soluble, π-stacking tetracene derivatives", Org. Lett., 8 (2), pp. 273–276, doi:10.1021/ol0526468, PMID 16408893
  14. H. Hart; C.-Y. Lai; G.C. Nwokogu; S. Shamouilian (1987), "Tetrahalobenzenes as diaryne equivalents in polycyclic arene synthesis", Tetrahedron, 43 (22), pp. 5203–5224, doi:10.1016/S0040-4020(01)87696-1
  15. C.-T. Lin; T.-C. Chou (1988), "Synthesis of 2,3-dibromoanthracene", Synthesis, 1988 (8), pp. 628–630, doi:10.1055/s-1988-27659
  16. F. Raymo; F.H. Kohnke; F. Cardullo (1992), "The regioselective generation of arynes from polyhalogenobenzenes. An improved synthesis of syn- and anti-1,4,5,8,9,12-hexahydro-1,4:5,8:9,12-triepoxytriphenylene", Tetrahedron (in German), 48 (33), pp. 6827–6838, doi:10.1016/S0040-4020(01)89874-4
  17. H. Hart; N. Raju; M.A. Meador; D.L. Ward (1983), "Synthesis of heptiptycenes with face-to-face arene rings via a 2,3:6,7-anthradiyne equivalent", J. Org. Chem., 48 (23), pp. 4357–4360, doi:10.1021/jo00171a039
  18. S. Eda, T. Hamura (2015), "Selective Halogen-Lithium Exchange of 1,2-Dihaloarenes for Successive [2+4] Cycloadditions of Arynes and Isobenzofurans", Molecules, 20 (10), pp. 19449–19462, doi:10.3390/molecules201019449, PMC 6331892, PMID 26512641
  19. S. Altarawneh; S. Behera; P. Jena; H.M. El-Kaderi (2014), "New insights into carbon dioxide interactions with benzimidazole-linked polymers", Chem. Commun., 50 (27), pp. 3571–3574, doi:10.1039/C3CC45901B, PMID 24567950
  20. T. Miyazaki; T. Yamagishi; M. Matsumoto (1987), "Determination and residual levels of 1,2,4,5-tetrabromobenzene and Mirex in human milk samples", Food Hygiene and Safety Science, 28 (2), pp. 125–129, doi:10.3358/shokueishi.28.125
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