• Finnish: arsiini
• Italian: arsina

• Finnish: -arsiini, arsiini-
• Italian: -arsina

• ttbc Portuguese: arsina
• ttbc Spanish: arsina

See also

• arsane
• arsonium
• arsorane

External links

Italian

Noun

arsine

1. Plural of arsina

Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is the simplest compound of arsenic. Aside from its lethality, it finds applications in the semiconductor industry and for the synthesis of organoarsenic compounds.

General properties

At its standard state, arsine is a colorless, denser-than-air gas that is soluble in water (200 mL/L) and in many organic solvents as well. Whereas arsine itself is odorless, owing to its oxidation by air it is possible to smell a slight, garlic-like scent when the compound is present at about 0.5 ppm. This compound is generally regarded as stable, since at room temperature it decomposes only slowly. At temperatures of ca. 230 °C decomposition to arsenic and hydrogen is rapid. Several factors, such as humidity, presence of light and certain catalysts (namely aluminium) facilitate the rate of decomposition.

4 AsCl3 + 3 NaBH4 → 4 AsH3 + 3 NaCl + 3 BCl3

This type of reaction was employed in the discovery of arsine as reported in 1775 by Carl Scheele who reduced arsenic(III) oxide with zinc in the presence of acid. This reaction is a prelude to the Marsh test, described below.

Alternatively, sources of As3− react with protonic reagents to also produce this gas:

Zn3As2 + 6 H+ → 2 AsH3 + 3 Zn2+

Reactions

The chemical properties of AsH3 are well developed and can be anticipated based on an average of the behavior of PH3 and SbH3.

Thermal decomposition

Typical for a heavy hydride (e.g., SbH3, H2Te, SnH4), AsH3 is unstable with respect to its elements. In other words, AsH3 is stable kinetically but not thermodynamically.

2 AsH3 → 3 H2 + 2 As

This decomposition reaction is the basis of the Marsh Test described below, which detects the metallic As.

Oxidation

Continuing the analogy to SbH3, AsH3 is readily oxidized by O2 or even air:

2 AsH3 + 3 O2 → As2O3 + 3 H2O

Arsine will react violently in presence of strong oxidizing agents, such as potassium permanganate, sodium hypochlorite or nitric acid.

Gutzeit test

A characteristic test for arsenic involves the reaction of AsH3 with Ag+, called the Gutzeit test for arsenic. Although this test has become obsolete in analytical chemistry, the underlying reactions further illustrate the affinity of AsH3 for "soft" metal cations. In the Gutzeit test, AsH3 is generated by reduction of aqueous arsenic compounds, typically arsenites, with Zn in the presence of H2SO4. The evolved gaseous AsH3 is then exposed to AgNO3 either as powder or as a solution. With "solid" AgNO3, AsH3 reacts to produce yellow Ag4AsNO3, whereas AsH3 reacts with a "solution" of AgNO3 to give black Ag3As.

Acid-base reactions

The acidic properties of the As–H bond are often exploited. Thus, AsH3 can be deprotonated:

AsH3 + NaNH2 → NaAsH2 + NH3

Upon reaction with the aluminium trialkyls, AsH3 gives the trimeric [R2AlAsH2]3, where R = (CH3)3C. This reaction is relevant to the mechanism by which GaAs forms from AsH3 (see below).

AsH3 is generally considered non-basic, but it can be protonated by "super acids" to give isolable salts of the tetrahedral species [AsH4]+.

Reaction with halogen compounds

Reactions of arsine with the halogens (fluorine and chlorine) or some of their compounds, such as nitrogen trichloride, are extremely dangerous and can result in explosions.

Forensic science and the Marsh test

AsH3 is also well known in forensic science because it is a chemical intermediate in the detection of arsenic poisoning. The old (but extremely sensitive) Marsh test generates AsH3 in the presence of arsenic. This procedure, developed around 1836 by James Marsh, is based upon treating a As-containing sample of a victim's body (typically the stomach) with As-free zinc and dilute sulfuric acid: if the sample contains arsenic, gaseous arsine will form. The gas is swept into a glass tube and decomposed by means of heating around 250–300 °C. The presence of As is indicated by formation of a deposit in the heated part of the equipment. The formation of a black mirror deposit in the cool part of the equipment indicates the presence of Sb.

The Marsh test was widely used by the end of the 19th century and the start of the 20th; nowadays more sophisticated techniques such as atomic spectroscopy, inductively coupled plasma and x-ray fluorescence analysis are employed in the forensic field. Though neutron activation analysis was used to detect trace levels of arsenic in the mid 20th century it has fallen out of use in modern forensics.

Toxicology

For the toxicology of other arsenic compounds, see Arsenic, Arsenic trioxide, and Arsenicosis. The toxicity of arsine is distinct from that of other arsenic compounds. The main route of exposure is by inhalation, although poisoning after skin contact has also been described. Arsine attacks haemoglobin in the red blood cells, causing them to be destroyed by the body.

The first signs of exposure, which can take several hours to become apparent, are headaches, vertigo and nausea, followed by the symptoms of haemolytic anaemia (high levels of unconjugated bilirubin), haemoglobinuria and nephropathy. In severe cases, the damage to the kidneys can be long-lasting.

Exposure to arsine concentrations of 250 ppm is rapidly fatal: concentrations of 25–30 ppm are fatal for 30 min exposure, and concentrations of 10 ppm can be fatal at longer exposure times. Symptoms of poisoning appear after exposure to concentrations of 0.5 ppm. There is little information on the chronic toxicity of arsine, although it is reasonable to assume that, in common with other arsenic compounds, a long-term exposure could lead to arsenicosis.

See also

• Arsenic
• Cacodylic acid
• Cacodyl oxide

Bibliography

Further reading

External links

• International Chemical Safety Card 0222
• IARC Monograph "Arsenic and Arsenic Compunds"
• NIOSH Pocket Guide to Chemical Hazards
• Data on arsine from Air Liquide