Tetrabromomethane

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Tetrabromomethane
Stereo, skeletal formula of tetrabromomethane
Stereo, skeletal formula of tetrabromomethane
Spacefill model of tetrabromomethane
Names
IUPAC name
Tetrabromomethane[2]
Other names
  • Carbon(IV) Bromide
  • Carbon Bromide
  • Carbon Tetrabromide
[1]
Identifiers
558-13-4 YesY
Abbreviations R-10B4[citation needed]
1732799
ChEBI CHEBI:47875 YesY
ChemSpider 10732 YesY
EC Number 209-189-6
26450
Jmol 3D model Interactive image
MeSH carbon+tetrabromide
PubChem 11205
RTECS number FG4725000
UN number 2516
Properties
CBr4
Molar mass 331.63 g·mol−1
Appearance Colorless to yellow-brown crystals
Odor sweet odor
Density 3.42 g mL−1
Melting point 94.5 °C; 202.0 °F; 367.6 K
Boiling point 189.7 °C; 373.4 °F; 462.8 K decomposes
0.024 g/100 mL (30 °C)
Solubility soluble in ether, chloroform, ethanol
Vapor pressure 5.33 kPa (at 96.3 °C)
1.5942 (100 °C)
Structure
Monoclinic
Tetragonal
Tetrahedron
0 D
Thermochemistry
0.4399 J K−1 g−1
212.5 J/mol K
26.0–32.8 kJ mol−1
47.7 kJ/mol
−426.2–−419.6 kJ mol−1
Vapor pressure {{{value}}}
Related compounds
Related alkanes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tetrabromomethane, CBr4, also known as carbon tetrabromide, is a carbon bromide. Both names are acceptable under IUPAC nomenclature.

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°.[3] Bond energy of C-Br is 235 kJ.mol−1.[4]

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.[3]

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 [5] 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. Similarly, CBr4 is used in combination with triphenylphosphine in the first step of the Corey-Fuchs reaction, which converts aldehydes into terminal alkynes. 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.[4]

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. "Carbon compounds: carbon tetrabromide". Retrieved 22 February 2013. 
  2. "carbon tetrabromide - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 26 March 2005. Identification. Retrieved 18 June 2012. 
  3. 3.0 3.1 F. Brezina, J. Mollin, R. Pastorek, Z. Sindelar. Chemicke tabulky anorganickych sloucenin (Chemical tables of inorganic compounds). SNTL, 1986.
  4. 4.0 4.1 N. N. Greenwood, A. Earnshaw. Chemie prvku (Chemistry of the Elements). Informatorium, Prague, 1993.
  5. 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