What Is Arsine Gas?
Arsine gas is a hydrogen compound of arsenic with the chemical formula AsH3.
It is also called hydrogen arsenide or arsenic hydride. Arsine gas is highly poisonous to humans, with an allowable time-weighted average concentration of 0.005 ppm.
When inhaled in large quantities by humans, it can affect the kidneys and blood, and in the worst case, cause death. Symptoms of arsine gas may be seen hours to days later and require medical follow-up.
Uses of Arsine Gas
Arsine gas is known as one of the semiconductor material gases used in the semiconductor manufacturing process. However, arsine gas is extremely toxic and can cause serious damage to the blood and kidneys. Therefore, contamination of the semiconductor manufacturing work environment by arsine gas has become a problem, and it is important to study optimal methods of quantifying arsine gas in the semiconductor manufacturing environment.
Arsine gas also produces arsenic when heated. This property can be used to detect trace amounts of arsenic. This method, called the Marsh test, was invented by James Marsh in 1836.
Properties of Arsine Gas
Arsine gas has a melting point of -117°C and a boiling point of -55°C. It exists as a colorless gas at room temperature and has a characteristic garlic odor.
In 100 g of water at 0°C, 0.0019 g of arsine gas is soluble. It is soluble in polar solvents and insoluble in organic solvents. The acid dissociation constant is pKa=25. Combustion yields water and arsenic trioxide (As2O3). It decomposes to arsenic and hydrogen by light, heat, and water.
The chemistry of arsine gas is predictable by the average of the corresponding pnictogen (PH3, SbH3, etc.). Arsine gas has reducing properties and reacts explosively with oxidants. It is flammable and should be handled with care. It reacts with aqueous silver nitrate solutions to liberate silver and has a standard redox potential of Eº = -0.225V. A high concentration of aqueous silver nitrate precipitates Ag3As-3AgNO3, a yellow compound salt containing silver arsenide.
Structure of Arsine Gas
Arsine gas is a compound of hydrogen and arsenic with a molecular weight of 77.95. Its density in gas is 4.93 g/L and in liquid form at -64°C is 1.640 g/mL.
The steric structure of arsine gas is similar to that of ammonia. ∠H-As-H is 91.8° and is a pyramidal molecule with three equivalent 1.519 Å As-H bonds. The hydrogen bond angles are smaller than those of ammonia and are close to right angles. Arsenic has an electronegativity of 2.0 and hydrogen has an electronegativity of 2.1. It is less polar than ammonia and does not form hydrogen bonds.
Other Information on Arsine Gas
1. Method of Synthesis of Arsine Gas
Arsine gas can be synthesized by adding zinc as a catalyst to a chemical containing arsenic and reacting it with dilute sulfuric acid. When arsine gas and hydrogen gas are burned and the flame touches a cold glass or porcelain dish, the single arsenic adheres to it, yielding a shiny arsenic mirror.
Arsine gas can also be produced by the reaction of calcium arsenide with dilute sulfuric acid. Decomposition of the pigment Scheele’s Green by bacteria or mold can produce arsine gas.
2. Characteristics of Organic Arsine Gas
Compounds in which the hydrogen atom of hydrogen arsenide is replaced by a hydrocarbon or halogen are also collectively called arsine gas. The general formula for a series of derivatives is RR1R2As. Each substituent represents an H or organic group. They generally have an unpleasant odor and are poisonous.
A specific example is methylarsine, whose chemical formula is CH3AsH2. Triphenylarsine is available as a ligand. Its chemical formula is (C6H5)3As.