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Osmic acid)
The chemical compound osmium tetroxide (OsO4) is an oxide of the element osmium, in which it attains its highest oxidation number of 8.
Osmium tetroxide sublimates at room temperature and is readily formed when powdered osmium is exposed to air. In fact it explains the name of the element, derived from a Greek word for stench. The oxide is a powerful staining agent in regular use in transmission electron microscopy (TEM) to provide contrast to the image. It also stains the human cornea, which can lead to blindness if proper safety precautions are not observed.
In organic synthesis it is sometimes used to oxidise alkenes to the dialcohols. One catalytic reaction with osmium tetroxide is the Sharpless bishydroxylation named after K. Barry Sharpless.
Osmium tetroxide is highly poisonous, even at very low exposure levels, and must be handled with appropriate precautions. In particular, inhalation at concentrations well below those at which a smell can be perceived can lead to edema of the lungs, and subsequent death. Noticeable symptoms can take hours to appear after exposure.
On the 6th April 2004 the American news organisation ABC News reported that British intelligence sources believed they had foiled a plot to detonate a bomb involving the chemical due to its poisonous properties.
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