Tetrabromomethane

Tetrabromomethane, CBr4, also known as carbon tetrabromide, is a carbon bromide. Both names are acceptable under IUPAC nomenclature, depending on whether it is considered as an organic or an inorganic compound.

Physical properties
Tetrabromomethane has two allotropes: crystaline II below 46.9 °C (320.0 K) and crystalline I above 46.9 °C. Monoclinic allotrope has space group C2/c with lattice constants: a = 20.9, b = 12.1, c = 21.2 (.10-1 nm), β = 110.5°. Bond energy of C-Br is 235 kJ.mol-1.

Due to its symmetrically substituted tetrahedral structure, its dipole moment is 0 Debye. Critical temperature is 439 °C (712 K) and critical pressure is 4.26 MPa.

Chemical reactions
In combination with triphenylphosphine, CBr4 is used in the Appel reaction, which converts alcohols to alkyl bromides. It is significantly less stable than lighter tetrahalomethanes.

It is prepared by methane bromination using HBr or Br2. It can be also prepared by more economical reaction of tetrachloromethane with aluminium bromide at 100 °C.

Uses
It is used as a solvent for greases, waxes and oils, in plastic and rubber industry for blowing and vulcanization, further for polymerization, as a sedative and as an intermediate in manufacturing agrochemicals. Due to its non-flammability it is used as an ingredient in fire resistant chemicals. It is also used for separating minerals because of its high density.