Hydrogen selenide

Hydrogen selenide (chemical formula: H₂Se) is a toxic and colorless gas with a distinct smell, reminiscent of rotten horseradish. It is the selenide analogue of water and a hydride of selenium. Hydrogen selenide is of significant importance in the chemical industry and biochemistry, particularly in the synthesis of selenium-containing compounds. However, its high toxicity and reactivity require careful handling and specific safety precautions.

Properties

Hydrogen selenide is a colorless, flammable gas under standard conditions. It has a boiling point of -41.25 °C and a melting point of -65.73 °C. The gas is slightly soluble in water, and its aqueous solution is weakly acidic. Hydrogen selenide readily decomposes into elemental selenium and hydrogen when heated or upon exposure to light.

Synthesis

Hydrogen selenide can be synthesized by the reaction of selenium powder with hydrogen gas at high temperatures. Another method involves the acidification of aqueous solutions containing selenides, which releases hydrogen selenide gas: \[ \text{Se}^{2-} + 2\text{H}^+ \rightarrow \text{H}_2\text{Se} \]

Toxicity

Hydrogen selenide is highly toxic, with exposure potentially resulting in severe respiratory distress, pulmonary edema, and even death. Its mechanism of toxicity involves the inhibition of mitochondrial enzymes, leading to cellular respiration failure. Safety measures when handling hydrogen selenide include the use of appropriate personal protective equipment (PPE), adequate ventilation, and gas detection systems.

Applications

Despite its toxicity, hydrogen selenide is used in the synthesis of selenium-containing compounds in both organic and inorganic chemistry. It serves as a precursor for the preparation of semiconductors, photovoltaic cells, and in the glass industry to impart red color to glass and ceramics. In biochemistry, hydrogen selenide is a key intermediate in the biosynthesis of selenocysteine, an amino acid found in several important enzymes, including glutathione peroxidase.

Environmental Impact

Hydrogen selenide can be released into the environment through industrial processes and natural volcanic activity. Its release into the atmosphere is a concern due to its toxicity and potential to form acidic rain, contributing to environmental pollution. Measures to reduce emissions include scrubbing waste gases and strict regulatory controls.

See Also

• Selenium
• Selenides
• Toxicology
• Environmental chemistry