Arsine (IUPAC name: arsane) is an inorganic compound with the formula AsH3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in the semiconductor industry and for the synthesis of organoarsenic compounds. The term arsine is commonly used to describe a class of organoarsenic compounds of the formula AsH3−xRx, where R = aryl or alkyl. For example, As(C6H5)3, called triphenylarsine, is referred to as "an arsine".
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||77.9454 g/mol|
|Density||4.93 g/l, gas; 1.640 g/mL (−64 °C)|
|Melting point||−111.2 °C (−168.2 °F; 162.0 K)|
|Boiling point||−62.5 °C (−80.5 °F; 210.7 K)|
|0.07 g/100 ml (25 °C)|
|Vapor pressure||14.9 atm|
Std enthalpy of
|Main hazards||Explosive, flammable, potential occupational carcinogen|
|Safety data sheet||See: data page|
|Extremely flammable (F+)|
Very toxic (T+)
Carc. Cat. 1
Dangerous for the environment (N)
|R-phrases (outdated)||R12, R26, R48/20, R50/53|
|S-phrases (outdated)||(S1/2), S9, S16, S28, S33, S36/37, S45, S60, S61|
|NFPA 704 (fire diamond)|
|Flash point||−62 °C (−80 °F; 211 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
|2.5 mg/kg (intravenous)|
LC50 (median concentration)
LCLo (lowest published)
|NIOSH (US health exposure limits):|
|TWA 0.05 ppm (0.2 mg/m3)|
|C 0.002 mg/m3 [15-minute]|
IDLH (Immediate danger)
|Ammonia; phosphine; stibine; bismuthine|
|Supplementary data page|
|Refractive index (n),|
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
At its standard state, arsine is a colorless, denser-than-air gas that is slightly soluble in water (20% at 20 °C) 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 or fish-like scent when the compound is present above 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.
AsH3 is a pyramidal molecule with H–As–H angles of 91.8° and three equivalent As–H bonds, each of 1.519 Å length.
Discovery and synthesis
- 4 AsCl3 + 3 NaBH4 → 4 AsH3 + 3 NaCl + 3 BCl3
Alternatively, sources of As3− react with protonic reagents to also produce this gas. Zinc arsenide and sodium arsenide are suitable precursors:
- Zn3As2 + 6 H+ → 2 AsH3 + 3 Zn2+
- Na3As + 3 HBr → AsH3 + 3 NaBr
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.
Continuing the analogy to SbH3, AsH3 is readily oxidized by concentrated O2 or the dilute O2 concentration in air:
- 2 AsH3 + 3 O2 → As2O3 + 3 H2O
Precursor to metallic derivatives
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.
The acidic properties of the As–H bond are often exploited. Thus, AsH3 can be deprotonated:
- AsH3 + NaNH2 → NaAsH2 + NH3
AsH3 is generally considered non-basic, but it can be protonated by superacids to give isolable salts of the tetrahedral species [AsH4]+.
Reaction with halogen compounds
In contrast to the behavior of PH3, AsH3 does not form stable chains, although H2As–AsH2 and even H2As–As(H)–AsH2 have been detected. The diarsine is unstable above −100 °C.
AsH3 is used in the synthesis of semiconducting materials related to microelectronics and solid-state lasers. Related to phosphorus, arsenic is an n-dopant for silicon and germanium. More importantly, AsH3 is used to make the semiconductor GaAs by chemical vapor deposition (CVD) at 700–900 °C:
- Ga(CH3)3 + AsH3 → GaAs + 3 CH4
For microelectronic applications, arsine can be provided via a sub-atmospheric gas source. In this type of gas package, the arsine is adsorbed on a solid microporous adsorbent inside a gas cylinder. This method allows the gas to be stored without pressure, significantly reducing the risk of an arsine gas leak from the cylinder. With this apparatus, arsine is obtained by applying vacuum to the gas cylinder valve outlet. For semiconductor manufacturing, this method is practical, as these processes usually operate under high vacuum.
Since before WWII AsH3 was proposed as a possible chemical warfare weapon. The gas is colorless, almost odorless, and 2.5 times denser than air, as required for a blanketing effect sought in chemical warfare. It is also lethal in concentrations far lower than those required to smell its garlic-like scent. In spite of these characteristics, arsine was never officially used as a weapon, because of its high flammability and its lower efficacy when compared to the non-flammable alternative phosgene. On the other hand, several organic compounds based on arsine, such as lewisite (β-chlorovinyldichloroarsine), adamsite (diphenylaminechloroarsine), Clark 1 (diphenylchloroarsine) and Clark 2 (diphenylcyanoarsine) have been effectively developed for use in chemical warfare.
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, published in 1836 by James Marsh, is based upon treating an As-containing sample of a victim's body (typically the stomach contents) 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. On the other hand, the appearance of a black mirror deposit in the cool part of the equipment indicates the presence of antimony (the highly unstable SbH3 decomposes even at low temperatures).
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 since fallen out of use in modern forensics.
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 hemoglobin 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.
It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act (42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.
Occupational exposure limits
|Argentina||Confirmed human carcinogen|
|Australia||TWA 0.05 ppm (0.16 mg/m3)|
|Belgium||TWA 0.05 ppm (0.16 mg/m3)|
|Bulgaria||Confirmed human carcinogen|
|Colombia||Confirmed human carcinogen|
|Denmark||TWA 0.01 ppm (0.03 mg/m3)|
|Egypt||TWA 0.05 ppm (0.2 mg/m3)|
|Hungary||TWA 0.2 mg/m3STEL 0.8 mg/m3|
|Jordan||Confirmed human carcinogen|
|Mexico||TWA 0.05 ppm (0.2 mg/m3)|
|Netherlands||MAC-TCG 0.2 mg/m3|
|New Zealand||TWA 0.05 ppm (0.16 mg/m3)|
|Norway||TWA 0.003 ppm (0.01 mg/m3)|
|Philippines||TWA 0.05 ppm (0.16 mg/m3)|
|Poland||TWA 0.2 mg/m3 STEL 0.6 mg/m3|
|Russia||STEL 0.1 mg/m3|
|Singapore||Confirmed human carcinogen|
|South Korea||TWA 0.05 ppm (0.2 mg/m3)|
|Sweden||TWA 0.02 ppm (0.05 mg/m3)|
|Switzerland||MAK-week 0.05 ppm (0.16 mg/m3)|
|Thailand||TWA 0.05 ppm (0.2 mg/m3)|
|Turkey||TWA 0.05 ppm (0.2 mg/m3)|
|United Kingdom||TWA 0.05 ppm (0.16 mg/m3)|
|United States||0.05 ppm (0.2 mg/m3)|
|Vietnam||Confirmed human carcinogen|
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- Scheele, Carl Wilhelm (1775) "Om Arsenik och dess syra" (On arsenic and its acid), Kongliga Vetenskaps Academiens Handlingar (Proceedings of the Royal Scientific Academy [of Sweden]), 36: 263-294. From p. 290: "Med Zinck. 30. (a) Denna år den endaste af alla så hela som halfva Metaller, som i digestion met Arsenik-syra effervescerar." (With zinc. 30. (a) This is the only [metal] of all whole- as well as semi-metals that effervesces on digestion with arsenic acid.) Scheele collected the arsine and put a mixture of arsine and air into a cylinder. From p. 291: "3:0, Då et tåndt ljus kom når o̊pningen, tåndes luften i kolfven med en småll, lågan for mot handen, denna blef o̊fvedragen med brun fårg, … " (3:0, Then as [the] lit candle came near the opening [of the cylinder], the gases in [the] cylinder ignited with a bang; [the] flame [rushed] towards my hand, which became coated with [a] brown color, … )
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- "40 C.F.R.: Appendix A to Part 355—The List of Extremely Hazardous Substances and Their Threshold Planning Quantities" (PDF) (July 1, 2008 ed.). Government Printing Office. Archived from the original (PDF) on February 25, 2012. Retrieved October 29, 2011. Cite journal requires
- "Arsine". RTECS. National Institute for Occupational Safety and Health (NIOSH).