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

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

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 is a general method of derivatizing hexabromobenzene. Benzene is sufficiently nucleophilic that it undergoes substitution by bromide ions to give the substituted derivatives, hexabromobenzene.

Properties
Hexabromobenzene is a white powder in physical form. It's not soluble in water but is soluble in ethanol, ether, and benzene. Molecular weigh t 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.

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.

Notably, the acute toxicity of HBB is observed to decrease with an increase in the number of bromine atoms in the molecule. 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.

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. 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.

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.

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.

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.