Tetrabromomethane

"CBr4" redirects here. For the Transport Canada location, see Clinton (Bleibler Ranch) Aerodrome.

Tetrabromomethane
IUPAC name Tetrabromomethane Carbon tetrabromide
Other names Methane tetrabromide, Carbon bromide, R-10B4
Identifiers
CAS number	558-13-4 Y
PubChem	11205
ChemSpider	10732 Y
EC number	209-189-6
UN number	2516
ChEBI	CHEBI:47875 Y
RTECS number	FG4725000
Jmol-3D images	Image 1
SMILES C(Br)(Br)(Br)Br
InChI InChI=1S/CBr4/c2-1(3,4)5 Y Key: HJUGFYREWKUQJT-UHFFFAOYSA-N Y InChI=1/CBr4/c2-1(3,4)5
Properties
Molecular formula	CBr4
Molar mass	331.63 g/mol
Appearance	Colorless solid
Density	3.42 g/cm3 2.961 g/cm3 (liquid, 100 °C)
Melting point	91.0 °C
Boiling point	189.5 °C (462.8 K)
Vapor pressure	5.33 kPa (96.3 °C)
Structure
Crystal structure	Monoclinic
Molecular shape	Tetrahedral
Hazards
MSDS	ICSC 0474
EU Index	Not listed
Flash point	Non-flammable
Related compounds
Related bromomethanes	Bromomethane Dibromomethane Bromoform
Related compounds	Tetrafluoromethane Tetrachloromethane Tetraiodomethane
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

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 polymorphs: crystalline II or β below 46.9 °C (320.0 K) and crystalline I or α above 46.9 °C. Monoclinic polymorph has space group C2/c with lattice constants: a = 20.9, b = 12.1, c = 21.2 (.10⁻¹ nm), β = 110.5°.^[1] Bond energy of C-Br is 235 kJ.mol⁻¹.^[2]

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.^[1]

Plastic crystallinity

The high temperature α phase is known as a plastic crystal phase. Roughly speaking, the CBr₄ are situated on the corners of the cubic unit cell as well as on the centers of its faces in an fcc arrangement. It was thought in the past that the molecules could rotate more or less freely (a 'rotor phase'), so that on a time average they would look like spheres. Recent work ^[3] has shown, however, that the molecules are restricted to only 6 possible orientations (Frenkel disorder). Moreover, they cannot take these orientations entirely independently from each other because in some cases the bromine atoms of neighboring molecules would point at each other leading to impossibly short distances. This rules out certain orientational combinations when two neighbor molecules are considered. Even for the remaining combinations displacive changes occur that better accommodate neighbor to neighbor distances. The combination of censored Frenkel disorder and displacive disorder implies a considerable amount of disorder inside the crystal which leads to highly structured sheets of diffuse scattered intensity in X-ray diffraction. In fact, it is the structure in the diffuse intensity that provides the information about the details of the structure.

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.^[2]

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.

References

1. ^ ^{a b} F. Brezina, J. Mollin, R. Pastorek, Z. Sindelar. Chemicke tabulky anorganickych sloucenin (Chemical tables of inorganic compounds). SNTL, 1986.
2. ^ ^{a b} N. N. Greenwood, A. Earnshaw. Chemie prvku (Chemistry of the Elements). Informatorium, Prague, 1993.
3. ^ Coupled orientational and displacive degrees of freedom in the high-temperature plastic phase of the carbon tetrabromide α-CBr4 Jacob C. W. Folmer, Ray L. Withers, T. R. Welberry, and James D. Martin. Physical Review B 77 in press

External links

• International Chemical Safety Card 0474
• NIOSH Pocket Guide to Chemical Hazards 0106
• MSDS at SIRI.org