The formula for carbon tetrabromide is CBr4. This compound is categorized as a tetrahalomethane, a type of haloalkane where four bromine atoms are bonded to a single carbon atom. It is an organobromine compound that exists as a dense, crystalline solid at room temperature. Carbon tetrabromide is primarily used in specialized chemical reactions and industrial formulations.
Decoding the Chemical Name
The systematic name “carbon tetrabromide” directly reveals the compound’s elemental composition and atomic ratios. The name follows the rules for naming binary molecular compounds, where “carbon” refers to the central carbon atom (C) and “bromide” indicates the presence of the halogen bromine (Br).
The prefix “tetra-” means four, specifying that four bromine atoms are bonded to the central carbon atom. This reflects carbon’s valence, as it typically forms four covalent bonds to achieve a stable electron configuration. In CBr4, the single carbon atom shares one electron with each of the four bromine atoms, resulting in four single covalent bonds.
The structure is also known by the IUPAC name tetrabromomethane. This name is derived from methane (CH4), where all four hydrogen atoms have been replaced by bromine atoms.
Molecular Geometry and Physical State
The CBr4 molecule adopts a highly symmetrical three-dimensional shape known as tetrahedral geometry. This structure is dictated by the four electron-pair domains around the central carbon atom, which repel each other to maximize distance. This arrangement places the four bromine atoms at the corners of a tetrahedron, with the carbon atom at the center.
In a perfect tetrahedron, the bond angle between any two C-Br bonds is approximately 109.5°. Although the individual C-Br bonds are polar due to the difference in electronegativity, the overall symmetrical arrangement causes the polarity of these bonds to cancel out precisely. This results in a net dipole moment of zero, making the entire carbon tetrabromide molecule non-polar.
The non-polar nature of the molecule, combined with its relatively high molecular weight of 331.63 grams per mole, contributes to its physical state at room temperature. Carbon tetrabromide is a solid, appearing as colorless to light yellow crystals with a high density (3.42 grams per cubic centimeter). The compound has a relatively high melting point for an organic molecule, typically between 88°C and 90°C.
Common Roles in Chemistry
Carbon tetrabromide is widely employed in laboratory and industrial processes, primarily functioning as a reagent and a specialized solvent. A major use is as a brominating agent in organic synthesis, providing bromine atoms to introduce into other molecules. It is frequently used in the Appel reaction, which converts alcohols into alkyl bromides when combined with triphenylphosphine.
The compound also plays a role in the Corey-Fuchs reaction, converting an aldehyde into a terminal alkyne. Beyond synthesis, its non-polar character allows it to function effectively as a solvent for non-polar substances like greases, waxes, and oils. This solvent application is particularly valuable in the plastic and rubber industries for processes such as vulcanization and polymerization.
Historically, carbon tetrabromide was incorporated into fire-resistant formulations due to its non-flammability. However, its use is now specialized due to toxicity and the risk of releasing toxic bromine fumes when heated to decomposition. Handling precautions are necessary, including working in well-ventilated areas and avoiding direct contact to mitigate potential irritation to the eyes, skin, and respiratory system.