1,2,4,5-Tetrabromobenzene

Last updated
1,2,4,5-Tetrabromobenzene
1,2,4,5-Tetrabrombenzol Struktur.svg
Names
Preferred IUPAC name
1,2,4,5-Tetrabromobenzene
Identifiers
3D model (JSmol)
ECHA InfoCard 100.010.231 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 211-253-3
PubChem CID
UNII
  • InChI=1S/C6H2Br4/c7-3-1-4(8)6(10)2-5(3)9/h1-2H
    Key: QCKHVNQHBOGZER-UHFFFAOYSA-N
  • C1=C(C(=CC(=C1Br)Br)Br)Br
Properties
C6H2Br4
Appearancewhite solid
Density 2.518 g/cm3
Melting point 180–182 °C (356–360 °F; 453–455 K)
Hazards
GHS labelling:
GHS-pictogram-exclam.svg
Warning
H315, H319, H335, H413
P261, P264, P271, P273, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

1,2,4,5-Tetrabromobenzene is an aryl bromide and a four-substituted bromobenzene 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]

Contents

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 1,2,4,5-Tetrabrombenzol Synthese.svg
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. Diskotische LC aus 1,2,4,5-Tetrabrombenzol.svg
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 Synthese eines symmetrischen Tetraalkoxystilbens.svg
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 Bildung von BBI-Salzen und Benzochinondiiminen.svg
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 Bildung eines 1,4-Monoarins mit Furan.svg
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 Dibromdioctylnaphthalin aus 1,2,4,5-Tetrabrombenzol.svg
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 Hexacen-Derivat aus 1,2,4,5-Tetrabrombenzol.svg
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 Vernetztes Benzimidazolpolymer.svg
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]

Related Research Articles

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<span class="mw-page-title-main">Dicarbonyl</span> Molecule containing two adjacent C=O groups

In organic chemistry, a dicarbonyl is a molecule containing two carbonyl groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls are in close enough proximity that their reactivity is changed, such as 1,2-, 1,3-, and 1,4-dicarbonyls. Their properties often differ from those of monocarbonyls, and so they are usually considered functional groups of their own. These compounds can have symmetrical or unsymmetrical substituents on each carbonyl, and may also be functionally symmetrical or unsymmetrical.

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References

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