Stibane

Stibine (IUPAC name: stibane) is a chemical compound with the formula SbH₃. A pnictogen hydride, this colourless, highly toxic gas is the principal covalent hydride of antimony, and a heavy analogue of ammonia. The molecule is pyramidal with H–Sb–H angles of 91.7° and Sb–H distances of 170.7 pm (1.707 Å). This gas has an offensive smell like hydrogen sulfide (rotten eggs).

Preparation

SbH₃ is generally prepared by the reaction of Sb³⁺ sources with H− equivalents:
:2 Sb₂O₃ + 3 LiAlH₄ → 4 SbH₃ + 1.5 Li₂O + 1.5 Al₂O₃
:4 SbCl₃ + 3 NaBH₄ → 4 SbH₃ + 3 NaCl + 3 BCl₃

Alternatively, sources of Sb³⁻ react with protonic reagents (even water) to also produce this unstable gas:
:Na₃Sb + 3 H₂O → SbH₃ + 3 NaOH

Properties

The chemical properties of SbH₃ resemble those for AsH₃. Typical for a heavy hydride (e.g. AsH₃, H₂Te, SnH₄), SbH₃ is unstable with respect to its elements. The gas decomposes slowly at room temperature but rapidly at 200 °C:
::2 SbH₃ → 3 H₂ + 2 Sb
The decomposition is autocatalytic and can be explosive.

SbH₃ is readily oxidized by O₂ or even air:
::2 SbH₃ + 3 O₂ → Sb₂O₃ + 3 H₂O

SbH₃ exhibits no basicity, but it can be deprotonated:
::SbH₃ + NaNH₂ → NaSbH₂ + NH₃

Uses

Stibine is used in the semiconductor industry to dope silicon with small quantities of antimony via the process of chemical vapour deposition (CVD). It has also been used as a silicon dopant in epitaxial layers. Reports claim the use of SbH₃ as a fumigant but its instability and awkward preparation contrast with the more conventional fumigant phosphine.

History

As stibine (SbH₃) is similar to arsine (AsH₃); it is also detected by the Marsh test. This sensitive test detects arsine generated in the presence of arsenic. This procedure, developed circa 1836 by James Marsh, treats a sample with arsenic-free zinc and dilute sulfuric acid: if the sample contains arsenic, gaseous arsine will form. The gas is swept into a glass tube and decomposed by means of heating around 250 – 300 °C. The presence of arsenic is indicated by formation of a deposit in the heated part of the equipment. The formation of a black mirror deposit in the cool part of the equipment indicates the presence of antimony.

In 1837 Lewis Thomson and Pfaff independently discovered stibine. It took some time before the properties of the toxic gas could be determined, partly because a suitable synthesis was not available. In 1876 Francis Jones tested several synthesis methods, but it was not before 1901 when Alfred Stock determined most of the properties of stibine.

Safety

SbH₃ is an unstable flammable gas. It is highly toxic, with an LC50 of 100 ppm in mice.

Toxicology

The toxicity of stibine is distinct from that of other antimony compounds, but similar to that of arsine. Stibine binds to the haemoglobin of red blood cells, causing them to be destroyed by the body. Most cases of stibine poisoning have been accompanied by arsine poisoning, although animal studies indicate that their toxicities are equivalent. The first signs of exposure, which can take several hours to become apparent, are headaches, vertigo, and nausea, followed by the symptoms of hemolytic anemia (high levels of unconjugated bilirubin), hemoglobinuria, and nephropathy.

See also

*Antimony (Sb)
*Arsine (AsH₃)
*Devarda's alloy, also used to produce arsine and stibine in the lab
*List of highly toxic gases
*Marsh test, first used to analyse AsH₃ and SbH₃
* James Marsh, invented the Marsh test in 1836
*Nascent hydrogen

References

External links

International Chemical Safety Card 0776
*

{{Hydrides by group

Antimony(III) compounds
Metal hydrides