Arsine

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Arsine
Image:Arsine.png Image:Arsine-3D-sticks.png Image:Arsine-3D-vdW.png
General
Systematic name	Arsane
Other names	arsenic trihydride arseniuretted hydrogen arsenous hydride hydrogen arsenide
Molecular formula	AsH₃
Molar mass	77.95 g/mol
Appearance	colourless gas
CAS number	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 (pK_b)	?
Structure
Molecular shape	trigonal pyramidal
Dipole moment	0.20 D
Thermodynamic data
Standard enthalpy of formation Δ_fH^o_gas	+66.4 kJ/mol
Standard molar entropy S^o_gas	223 kJ.K⁻¹.mol⁻¹
Hazards
MSDS	External MSDS
EU classification	Very flammable Highly toxic Dangerous for the environment
NFPA 704	Image:NFPA 704.svg 4 4 2
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, ε_r, 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) Infobox disclaimer and references

Arsine, the simplest compound of arsenic, is As H₃. 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. <ref name="INRS">Institut National de Recherche et de Sécurité (2000). "Fiche toxicologique nº 53: Trihydrure d'arsenic" (PDF). Retrieved on 2006-09-06.</ref>

At its standard state, arsine appears in the form of a colorless, denser than air gas that is soluble in water (200 ml/l) and in many organic solvents as well. While 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 its decomposition into arsenic and hydrogen at room teperature takes place very slowly, unless a temperature of 230 °C is reached. Several factors, such as humidity, presence of light and certain catalysts (namely aluminium) facilitate the decomposition of arsine. <ref name="INRS"/>

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 AsH_3-xR_x, where R = aryl or alkyl. For example, As(C₆H₅)₃, called triphenylarsine, is referred to as an arsine.

1 Discovery
2 Synthesis
3 Reactions
4 Microelectronics applications
5 Chemical warfare applications
6 Forensic science and the Marsh test
7 Toxicology
8 See also
9 Bibliography
10 External links

[edit] 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.

[edit] Synthesis

AsH₃ is generally prepared by the reaction of As³⁺ sources with H⁻ equivalents. <ref name="Bellama">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</ref> <ref name="Holleman">Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001</ref>

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

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

Zn₃As₂ + 6 H⁺ → 2 AsH₃ + 3 Zn²⁺

[edit] 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.

[edit] 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.

[edit] 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. <ref name="INRS"/>

[edit] 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. <ref name="Herrmann">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</ref>

[edit] Gutzeit test

A characteristic test for arsenic involves the reaction of AsH₃ with Ag⁺, called the Gutzeit test for arsenic. <ref name="King">King, E. J. "Qualitative Analysis and Electrolytic Solutions" Harcourt, Brace, and World; New York (1959)</ref> 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.

[edit] 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. <ref name="Atwood">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</ref> 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]⁺. <ref name="Minkwitz">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.</ref>

[edit] 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. <ref name="INRS"/>

[edit] 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.

[edit] 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 germanium. <ref name="INRS"/> More importantly, AsH₃ is used to make the semiconductor GaAs by CVD at 700-900 °C:

Ga(CH₃)₃ + AsH₃ → GaAs + 3 CH₄

[edit] 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 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 (diphenylaminearsine), Clark I (diphenylchlorarsine) and Clark II, (diphenylcyanoarsine) have been effectively developed for use in chemical warfare. <ref name="Suchard">Suchard, Jeffrey R. (March 2006). "CBRNE - Arsenicals, Arsine" (HTML). eMedicine. Retrieved on 2006-09-05.</ref>

[edit] 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. <ref name="Holleman"/> 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.

[edit] Toxicology

For the toxicology of other arsenic compounds, see Arsenic, Arsenic trioxide and Arsenicosis. <ref name="Minkwitz"/>

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.

[edit] See also

[edit] Bibliography

Hatlelid K. M. (1996). "Reactions of Arsine with Hemoglobine". Journal of Toxicology and Environmental Health Part A 47 (2): 145 - 157. DOI:10.1080/009841096161852.
Nielsen H. H. (1952). "The Molecular Structure of Arsine". The Journal of Chemical Physics 20 (12): 1955-1956. DOI:10.1063/1.1700347.
Fowler B. A., Weissberg J. B. (1974). "Arsine poisoning". New England Journal of Medicine 300: 1171–1174.