Tetrabromomethane

Tetrabromide

Colorless crystals with a sweet odor

Fixed

3.42 g · cm -3

90.1 ° C

189.5 ° C

Practically insoluble in water

1.5942 (100 ° C)

Risk

1000 mg · kg -1 ( LD50, rat, oral)

29.4 kJ / mol

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Tetrabromomethane (also tetrabromide ) is a chemical compound from the series of bromohydrocarbons. For him, all the hydrogen atoms of methane are replaced by bromine atoms. Both designations are according to IUPAC nomenclature correctly, depending on whether the connection as organic ( carbon tetrabromide ) or inorganic ( carbon tetrabromide ) compound is considered.

Representation

Tetrabromomethane is prepared by bromination of methane with elemental bromine. Economic the halogen exchange is by the reaction of carbon tetrachloride with aluminum bromide at 100 ° C.

Properties

Physical Properties

Tetrabromomethane is a colorless, non-combustible solid having a melting point of 90.1 ° C, which is present at room temperature in the form of monoclinic crystals. The boiling point is 189.5 ° C. Tetrabromomethane is as good as not very soluble in nonpolar solvents such as chloroform or toluene in water.

Due to the spherical shape of CBr4 molecule tetrabromomethane has an exceptionally high cryoscopic constant. This means that cause quite a high melting point depression in CBr4 solutes. It is therefore very suitable as a solvent for the method of molecular weight determination by Rast. The cryoscopic constant is 80 kg · K · mol -1.

Tetrabromomethane is polymorphic, that is, it occurs in two modifications ( α - modification and β - modification ) that convert at 46.9 ° C into each other.

The binding energy of the C- Br bond is 235 kJ · mol -1.

Due to the highly symmetric tetrahedral structure, the dipole moment is 0 Debye. The critical temperature is 439 ° C ( 712 K) at a critical pressure of 4.26 MPa.

The critical temperature is 724.8 K ( 451.65 ° C), and the critical pressure 96.3 bar, corresponding to 9.63 MPa.

Chemical Properties

Tetrabromomethane is considerably less stable than the two lighter tetra halomethanes tetrafluoromethane and tetrachloromethane. It is relatively easy from a bromine atom, which is why it can be used as a mild brominating agent.

Use

CBr4 in combination with triphenylphosphine is used as the alkylating agent in the so-called Appel reaction, to convert alcohols into bromides.

Tetrabromide can be used for p-type doping of gallium arsenide with carbon ( GaAs: C ) can be used by molecular beam epitaxy ( MBE).

Due to its high density in the molten state can be used as tetrabromomethane heavy liquid for separating minerals.