Hexabromobenzene

Hexabromobenzene is an aryl bromide and a six-substituted bromobenzene in which all six positions of the central benzene ring are bonded to a bromine atom.

Hexabromobenzene

Names
Preferred IUPAC name Hexabromobenzene
Other names Perbromobenzene HBB
Identifiers
CAS Number	87-82-1 Y
3D model (JSmol)	Interactive image
ChemSpider	6639
ECHA InfoCard	100.001.613
PubChem CID	6905
UNII	T01859XWIR Y
CompTox Dashboard (EPA)	DTXSID1024128
InChI InChI=1S/C6Br6/c7-1-2(8)4(10)6(12)5(11)3(1)9 Key: CAYGQBVSOZLICD-UHFFFAOYSA-N InChI=1/C6Br6/c7-1-2(8)4(10)6(12)5(11)3(1)9 Key: CAYGQBVSOZLICD-UHFFFAOYAA
SMILES C1(=C(C(=C(C(=C1Br)Br)Br)Br)Br)Br
Properties
Chemical formula	C6Br6
Molar mass	551.490 g·mol−1
Appearance	Monoclinic needles or white powder.[1]
Odor	Odorless[2]
Melting point	327 °C (621 °F; 600 K)[2]
Solubility in water	0.16x10−3 mg/L (insoluble)[1]
Solubility	Slightly soluble in Ethanol, Diethyl ether[3]
Solubility in Acetic acid	Soluble[3]
Solubility in Benzene	10%[4]
Solubility in Chloroform	10%[4]
Solubility in Petroleum ether	10%[4]
log P	6.07[1]
Hazards
GHS labelling:
Pictograms	[2]
Signal word	Danger[2]
Hazard statements	H302, H312, H315, H319, H332, H335, H413[1]
Precautionary statements	P261, P264, P270, P271, P280, P301+P312, P302+P352, P304+P312, P304+P340, P305+P351+P338, P312, P321, P322, P330, P332+P313, P362, P363, P403+P233, P405, P501[1]
NFPA 704 (fire diamond)	2 0 0
Safety data sheet (SDS)	LCSS 6905
Related compounds
Related compounds	Hexafluorobenzene Hexachlorobenzene Hexaiodobenzene
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Hexabromobenzene has seen use in high voltage capacitors as a flame retardant.^[5] It also has applications as a starting material in the formation of thin graphene-like films for low cost energy storage devices and capacitors.^[6]

Preparation

It can be prepared by reacting benzene (C₆H₆) with 6 equivalents of bromine (Br₂) in the presence of heat and UV light. This reaction is known as the bromination of Benzene:

${\displaystyle {\ce {C6H6 + 6 Br2 -> C6Br6 + 6HBr}}}$

Apart from hexabromobenzene, the reaction produces six equivalents of Hydrogen Bromide (HBr).

Reaction

The reaction to form Hexabromobenzene, known as Bromination of Benzene, involves substitution of hydrogens by bromides. Electrophilic aromatic substitution^[7] is a general method of derivatizing hexabromobenzene. Benzene is sufficiently nucleophilic that it undergoes substitution by bromide ions to give the substituted derivatives, hexabromobenzene.^[8]

Properties

Hexabromobenzene is a white powder in physical form. It's not soluble in water but is soluble in ethanol, ether, and benzene. Molecular weight is 551.7 g/mol. Melting point of 327 °C. Whiteness percent of 93.0. Its bromine content is above 86%, and it represents high efficacy. Incompatible with strong oxidizing agents. It has excellent integration flexibility with several resins and plastics due to its solubility in substances like ethanol, ether, and benzene.^[9]

Dangers

Hexabromobenzene (HBB) poses significant dangers due to its toxicity profile as classified by the GHS (Globally Harmonized System of Classification and Labeling of Chemicals). Classified as GHS07, HBB exhibits acute toxicity via oral, dermal, and inhalation routes, categorizing it under category 4 for this hazard. Additionally, it induces skin and eye irritation, classified under category 2 for both. Moreover, HBB is known to cause skin sensitization (category 1) and specific target organ toxicity upon single exposure (category 3), with the respiratory system being the primary target organ.^[10]

Notably, the acute toxicity of HBB is observed to decrease with an increase in the number of bromine atoms in the molecule.^[11] However, the potential for necrotic changes varies based on the position of these bromine atoms within the molecule. There are severe health risks associated with HBB exposure, warranting careful handling and stringent safety measures in its use and management.^[10]

Uses

Hexabromobenzene (HBB) finds extensive use as a fire retardant additive in a range of materials including plastics, paper, and electrical goods, where it serves as a top-tier flame retardant. With an impressive melting point of 327 °C and a high bromide content of 86%, HBB significantly enhances the fire safety of these materials.^[12] Its ability to suppress combustion effectively makes it a sought-after choice in industries concerned with fire prevention. However, its widespread application also leads to its dispersion in the environment. Additionally, HBB can undergo proto bromination reactions when treated with sodium methoxide in methanol and ethyl methyl ketone, yielding a mixture of tribromobenzene.Despite its efficacy in fire retardation, the environmental and health impacts of HBB underscore the importance of careful handling and monitoring in its utilization.^[10]

Applications

The influences of five organic cosolvents (acetone, methanol, ethanol, THF, or DMSO) on hexabromobenzene (HBB) degradation catalyzed by one typical reactive material montmorillonite-templated sub nanoscale zero-valent iron (CZVI) was investigated. The CZVI-catalyzed HBB degradation mechanism was proposed as the electron transfer between zero-valent iron and HBB, which led to formation of four debromination products.^[11]

hexabromobenzene also serves as one of the key polyhalogenated aromatic compounds used in the bottom-up synthesis process of graphene-like films. Through electrochemical reduction, HBB contributes to the formation of polyaromatic ring structures alongside other compounds like hexafluorobenzene (HFB) and hexachlorobenzene (HCB). It facilitates the creation of graphene-like carbon films upon thermal annealing, offering a cost-effective approach without the need for sophisticated equipment.^[6]

Hexabromobenzene (HBB) was utilized in a study investigating its metabolic fate in female rats, wherein the substance was orally administered at doses of 16.6 mg/kg body weight every other day for a span of 2 weeks. Analysis of the rats' excreta revealed the presence of various metabolites, including unchanged HBB, penta bromobenzene, as well as oxygen- and sulfur-containing compounds.^[13]

References

1. CID 6905 from PubChem
2. Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
3. Weast, R.C. (1979). Handbook of Chemistry and Physics (60 ed.). Boca Raton, Florida: CRC Press Inc. p. C-165. ISBN 9780849315565.
4. Weast, Robert C.; Astle, Melvin J. (1985). CRC Handbook of Data On Organic Compounds. Vol. 1. Boca Raton, Florida: CRC Press Inc. p. 176. ISBN 9780849304002.
5. US Grant 6909590, Tsukasa Sato, Isao Fujiwara, Makoto Morita, Kenichi Horikawa, "High voltage capacitor and magnetron", published 2004-08-09, issued 2005-06-21, assigned to TDK Corp
6. Kudaş, Züleyha; Gür, Emre; Ekinci, Duygu (11 June 2018). "Synthesis of Graphene-like Films by Electrochemical Reduction of Polyhalogenated Aromatic Compounds and their Electrochemical Capacitor Applications". Langmuir. 34 (27): 7958–7970. doi:10.1021/acs.langmuir.8b01177. PMID 29890834.
7. "18.1: Electrophilic Aromatic Substitution (EAS)". Chemistry LibreTexts. 2016-02-19. Retrieved 2024-02-11.
8. TOMLINSON, MURIEL (1971), "Benzene and Its Homologues: the Substitution Reactions of Benzene", An Introduction to the Chemistry of Benzenoid Compounds, Elsevier, pp. 12–27, retrieved 2024-02-11
9. PubChem. "Hexabromobenzene". pubchem.ncbi.nlm.nih.gov. Retrieved 2024-02-11.
10. "Hexabromobenzene". Sigma-Aldrich. August 27, 2023. Archived from the original on January 13, 2024. Retrieved February 3, 2024.
11. Peng, Anping; Gao, Hu; Wang, Huimin; Wang, Yi; Chen, Zeyou (July 2023). "Influence of organic cosolvents on hexabromobenzene degradation in solution by montmorillonite-templated subnanoscale zero-valent iron". Environmental Research. 229: 115986. doi:10.1016/j.envres.2023.115986.
12. "Premium 98% Pure Hexabromobenzene for Enhanced Fire Resistance & Versatility". Procurenet Limited. Retrieved 2024-02-11.
13. Koss, G; Doring, H; Wurminghausen, B; Koransky, W (November 1982). "Metabolic fate of hexabromobenzene in rats". Toxicology Letters. 14 (1–2): 69–77. doi:10.1016/0378-4274(82)90011-X.