Silicon Tetrabromide - Reactivity

Reactivity

Like other halosilanes, SiBr₄ can be converted to hydrides, alkoxides, amides, and alkyls, i.e., products with the following functional groups: Si-H, Si-OR, Si-NR₂, Si-R, and Si-X bonds respectively.

Silicon tetrabromide can be readily reduced by hydrides or complex hydrides.

4 R₂AlH + SiBr₄ → SiH₄ + 4 R₂AlBr

Reactions with alcohols and amines proceeed as follows:

SiBr₄ + 4 ROH → Si(OR)₄ + 4 HBr

SiBr₄ + 8 HNR₂ → Si(NR₂)₄ + 4 HNR₂HBr

Grignard reactions with metal alkyl halides are particularly important reactions due to their production of organosilicon compounds which can be converted to silicones.

SiBr₄ + n RMgX → R_nSiBr_4-n + n MgXBr

Redistribution reactions occur between two different silicon tetrahalides (as well as halogenated polysilanes) when heated to 100 ˚C, resulting in various mixed halosilanes. The melting points and boiling points of these mixed halosilanes generally increase as their molecular weights increase. (Can occur with X= H, F, Cl, Br, and I)

2 SiBr₄ + 2 SiCl₄ → SiBr₃Cl + 2 SiBr₂Cl₂ + SiBrCl₃

Si₂Cl₆ + Si₂Br₆ → Si₂Cl_nBr_6-n

Silicon tetrabromide hydrolyzes readily when exposed to air causing it to fume:

SiBr₄ + 2 H₂O → SiO₂ + 4 HBr

Silicon tetrabromide is stable in the presence of oxygen at room temperature, but bromosiloxanes form at 670-695 ˚C .

2 SiBr₄ + 1⁄2 O₂ → Br₃SiOSiBr₃ + Br₂