Tetrabromomethane

Tetrabromomethane
IUPAC name Tetrabromomethane[1]
Other names Carbon(IV) Bromide Carbon Bromide Carbon Tetrabromide [2]
Identifiers
Abbreviations	R-10B4[citation needed]
CAS number	558-13-4 Y
PubChem	11205
ChemSpider	10732 Y
EC number	209-189-6
UN number	2516
MeSH	carbon+tetrabromide
ChEBI	CHEBI:47875 Y
RTECS number	FG4725000
Beilstein Reference	1732799
Gmelin Reference	26450
Jmol-3D images	Image 1
SMILES BrC(Br)(Br)Br
InChI InChI=1S/CBr4/c2-1(3,4)5 Y Key: HJUGFYREWKUQJT-UHFFFAOYSA-N Y
Properties
Molecular formula	CBr4
Molar mass	331.63 g mol−1
Appearance	Colorless crystals
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
Vapor pressure	5.33 kPa (at 96.3 °C)
Structure
Crystal structure	Monoclinic
Coordination geometry	Tetragonal
Molecular shape	Tetrahedron
Dipole moment	0 D
Thermochemistry
Std enthalpy of formation ΔfHo298	26.0–32.8 kJ mol−1
Std enthalpy of combustion ΔcHo298	−426.2–−419.6 kJ mol−1
Specific heat capacity, C	145.9 J K−1 mol−1
Hazards
MSDS	inchem.org
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H302, H315, H318, H335
GHS precautionary statements	P261, P280, P305+351+338
EU classification	Xi N
R-phrases	R37/38, R41, R52/53
S-phrases	S26, S36
NFPA 704	0 2 0
LD50	56 mg kg−1 (intravenous, mouse) 1.8 g kg−1 (oral, rat)
Related compounds
Related alkanes	Dibromomethane Bromoform 1,1-Dibromoethane 1,2-Dibromoethane Tetrabromoethane
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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

External links

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