Hydrogen sulfide

Hydrogen sulfide (formula: $H_{2}S$) is a chemical compound which occurs as a colourless gas with acidic properties. Its characteristic odor, which resembles that of rotten eggs makes the identification of the compound easy.

It is present in the atmosphere (in low concetrations, less than 0.0003ppm) and also works as a signaling molecule for many animals, including humans. Its odor can be identified at concentrations of around 0.1 to 0.15ppm. As the concentration increases, it obtains a sweet odor and becomes deadly.

It's corrosive and flammable.

One should not forget that our bodies can produce hydrogen sulfide with the help of speicifc bacteria found in our mouth and intestines.

These take advantage of the sulfur found in proteins that we consume (four aminoacids, the buldings blocks of proteins, contain sulfur).

$S+H_2\to H_{2}S$ at $450^{o}C$

Sulfur that occurs as an unwanted compound in natural gas is also removed by hydrogenation, which yields hydrogen sulfide.

Created by the german chemist Carl Friedrich Claus, it makes it possible to convert hydrogen sulfide (from natural gas) to elemental sulfur.
The overall reaction can be descibed as follows:

The Claus' process served as a better replacement of the Frasch process, which obtained elemental sulfur from naturally found deposits underground.