A toxic, flammable gas with a characteristic rotten-egg smell, composed of hydrogen and sulfur.Hydrogen sulfide (H₂S) is a colorless, toxic, and flammable gas with a distinctive odor of rotten eggs. It is composed of two hydrogen atoms bonded to one sulfur atom. In nature, it is produced by the decomposition of organic matter in oxygen-poor environments, such as swamps, sewers, and volcanic gases. It is also a byproduct of industrial processes like petroleum refining and wastewater treatment. Despite its toxicity, it plays a role in biological signaling in small amounts.
Hydrogen sulfide is a simple molecule with a bent shape. It is a weak acid in water, dissociating to form hydrosulfide (HS⁻) and sulfide (S²⁻) ions. Its toxicity arises from its ability to bind to the iron in cytochrome c oxidase, an enzyme critical for cellular respiration, thereby blocking oxygen use and causing cellular asphyxiation. The rotten-egg smell is detectable at very low concentrations, but at higher concentrations it paralyzes the sense of smell, making it even more dangerous.
Hydrogen sulfide is used in analytical chemistry to precipitate metal sulfides, in the production of sulfuric acid, and as a precursor for organosulfur compounds. It is also studied for its role in physiological processes, such as vasodilation.
At high concentrations, hydrogen sulfide quickly deadens the sense of smell, so a person may no longer notice the 'rotten egg' odor even as the gas becomes lethal.
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