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Arsine

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Arsine
Arsine100px80px
General
Systematic name Arsane
Other names arsenic trihydride
arseniuretted hydroge
arsenous hydride
hydrogen arsenide
Molecular formula AsH3
Molar mass 77.95 g/mol
Appearance colourless gas
CAS number CAS=-->7784-42-1
Properties
Density and phase 4.93 g/l, gas
1.640 g/mL (-64 °C)
Solubility in water 0.07 g/100 ml (25 °C)
Solubility in organic solvents soluble
Melting point -117 °C (157 K)
Boiling point -62.5 °C (210 K)
Basicity (pKb) ?
Structure
Molecular shape trigonal pyramidal
Dipole moment 0.20 D
Thermodynamic data
Standard enthalpy
of formation ΔfHogas 		+66.4 kJ/mol
Standard molar entropy
Sogas 		223 kJ.K−1.mol−1
Hazards
MSDS External MSDS
EU classification Very flammable
Highly toxic
Dangerous for
the environment
NFPA 704 nfpa_h4.pngnfpa_f4.pngnfpa_r2.png
R-phrases R12, R26, R48/20
R50/53
S-phrases S1/2, S9, S16,
S28, S33, S36/37,
S45, S60, S61
Flash point flammable gas
Autoignition temperature ? °C
Explosive limits 4.5–78
Supplementary data page
Structure and
properties 		n, εr, etc.
Thermodynamic
data 		Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Related compounds
Related hydrides Ammonia
Phosphine
Stibine
Bismuthine
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
[Chemical infoboxInfobox disclaimer and references]

Arsine, the simplest compound of arsenic, is AsH3. It is a flammable, pyrophoric, and highly toxic molecular derivative of arsenic and hydrogen. The compound is of interest for its lethality, its applications in the semiconductor industry, and its use in the synthesis of organoarsenic species.

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. 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.

Contents

Discovery

AsH3 was discovered in 1775 by Carl Scheele from the reduction of arsenic(III) oxide with zinc and acid. This reaction is a prelude to the Marsh test, described briefly below.

Synthesis

AsH3 is generally prepared by the reaction of As3+ sources with H− equivalents.↑ ,↑ 
:AsCl3 + 3/4 NaBH4 → AsH3 + 0.75 NaCl + 0.75 BCl3
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 reasonably well developed and could 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

Precursor to metallic derivatives

AsH3 is used as a precursor to metal complexes of "naked" (or "nearly naked") As. Illustrative is the dimanganese species [(C5H5)Mn(CO)2]2AsH, wherein the Mn2AsH core is planar.↑ 

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]+.↑ 

Catenation

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.

Microelectronics applications

AsH3 is used in the synthesis of semiconducting materials related to microelectronics and solid-state lasers. Related to P, As is an n-dopant for silicon and gemanium. More importantly, AsH3 is used to make the semiconductor GaAs by CVD at 700-900 °C:
:Ga(CH3)3 + AsH3 → GaAs + 3 CH4

Chemical warfare applications

Since before WWII AsH3 was proposed as a possible chemical warfare weapon. The gas is colorless, almost odourless, and 2.5 times more dense than air, as required for a blanketing effect sought in chemical warfare. It is also lethal in concentrations far lower that 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 (diphenylaminearsine), Clark I (diphenylchlorarsine) and Clark II, (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 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 sulphuric 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 neutron activation analysis are employed in the forensic field.

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 binds to the haemoglobin of 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

Bibliography

  1. ↑  Bellama, J. M.; MacDiarmid, A. G. "Synthesis of the Hydrides of Germanium, Phosphorus, Arsenic, and Antimony by the Solid-Phase Reaction of the Corresponding Oxide with Lithium Aluminum Hydride" Inorganic Chemistry, 1968, vol. 7, page 2070-2.
  2. ↑  Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001.
  3. ↑  Herrmann, W. A.; Koumbouris, B.; Schaefer, A.; Zahn, T.; Ziegler, M. L. “Generation and Complex Stabilization of Arsinidene and Diarsine Fragments by Metal-Induced Degradation of Monoarsine” Chemische Berichte (1985), vol. 118, pages 2472-88.
  4. ↑  King, E. J. "Qualitative Analysis and Electrolytic Solutions" Harcourt, Brace, and World; New York (1959)..
  5. ↑  Atwood, D. A.; Cowley, A. H.; Harris, P. R.; Jones, R. A.; Koschmieder, S. U.; Nunn, C. M.; Atwood, J. L.; Bott, S. G. “Cyclic Trimeric Hydroxy, Amido, Phosphido, and Arsenido Derivatives of aluminum and gallium. X-ray Structures of [tert-Bu2Ga(m-OH)]3 and [tert-Bu2Ga(m-NH2)]3” Organometallics (1993), vol. 12, pages 24-29.
  6. ↑  R. Minkwitz, R.; Kornath, A.; Sawodny, W.; Härtner, H. “Über die Darstellung der Pnikogenoniumsalze AsH4+SbF6-, AsH4+AsF6-, SbH4+SbF6-" Zeitschrift für anorganische und allgemeine Chemie
Vol. 620, pages 753 - 756.
  1. ↑  Institut national de recherche et de sécurité (INRS), Fiche toxicologique nº 53 : Trihydrure d'arsenic, 2000.

External links

 

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