Arsine (IUPAC name: arsane) is an inorganic compound with the formulaAsH3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic.[4] 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".
General properties
In its standard state arsine is a colorless, denser-than-air gas that is slightly soluble in water (2% at 20 °C)[1] and in many organic solvents as well.[citation needed] Arsine itself is odorless,[5] but it oxidizes in air and this creates a slight garlic or fish-like scent when the compound is present above 0.5ppm.[6] This compound is kinetically stable: at room temperature it decomposes only slowly. At temperatures of ca. 230 °C, decomposition to arsenic and hydrogen is sufficiently rapid to be the basis of the Marsh test for arsenic presence. Similar to stibine, the decomposition of arsine is autocatalytic, as the arsenic freed during the reaction acts as a catalyst for the same reaction.[7] Several other factors, such as humidity, presence of light and certain catalysts (namely alumina) facilitate the rate of decomposition.[8]
AsH3 is a trigonal pyramidal molecule with H–As–H angles of 91.8° and three equivalent As–H bonds, each of 1.519 Å length.[9]
Discovery and synthesis
AsH3 is generally prepared by the reaction of As3+ sources with H− equivalents.[10]
4 AsCl3 + 3 NaBH4 → 4 AsH3 + 3 NaCl + 3 BCl3
As reported in 1775, Carl Scheele reduced arsenic(III) oxide with zinc in the presence of acid.[11] This reaction is a prelude to the Marsh test.
Alternatively, sources of As3− react with protonic reagents to also produce this gas. Zinc arsenide and sodium arsenide are suitable precursors:[12]
Zn3As2 + 6 H+ → 2 AsH3 + 3 Zn2+
Na3As + 3 HBr → AsH3 + 3 NaBr
Reactions
The understanding of the chemical properties of AsH3 is well developed and can be anticipated based on an average of the behavior of pnictogen counterparts, such as 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, it is stable kinetically but not thermodynamically.
2AsH3 → 3H2 + 2As
This decomposition reaction is the basis of the Marsh test, which detects elemental As.
Oxidation
Continuing the analogy to SbH3, AsH3 is readily oxidized by concentrated O2 or the dilute O2 concentration in air:
AsH3 is used as a precursor to metal complexes of "naked" (or "nearly naked") arsenic. An example is the dimanganese species [(C5H5)Mn(CO)2]2AsH, wherein the Mn2AsH core is planar.[13]
Gutzeit test
A characteristic test for arsenic involves the reaction of AsH3 with Ag+, called the Gutzeit test for arsenic.[14] 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.[15] 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 superacids to give isolable salts of the tetrahedral species [AsH4]+.[16]
In contrast to the behavior of PH3, AsH3 does not form stable chains, although diarsine (or diarsane) H2As–AsH2, and even triarsane H2As–As(H)–AsH2 have been detected. The diarsine is unstable above −100 °C.
For microelectronic applications, arsine can be provided by a sub-atmospheric gas source (a source that supplies less than atmospheric pressure). 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 feasible, as processes such as ion implantation operate under high vacuum.
Chemical warfare
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.[17]
AsH3 is 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.[4] This procedure, published in 1836 by James Marsh,[18] 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.[19][20]
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.[3] 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.[citation needed]
Arsine can cause pneumonia in two different ways either the "extensive edema of the acute stage may become diffusely infiltrated with polymorphonuclear leucocytes, and the edema may change to ringed with leucocytes, their epithelium degenerated, their walls infiltrated, and each bronchiole the center of a small focus or nodule of pneumonic consolidation", and In the second Case "the areas involved are practically always the anterior tips of the middle and upper lobes, while the posterior portions of these lobes and the whole of the lower lobes present an air-containing and emphysematous condition, sometimes with slight congestion, sometimes with none." which can result in death.[21]
^ abHolleman, A. F.; Wiberg, E. (2001) Inorganic Chemistry Academic Press: San Diego, ISBN0-12-352651-5.
^Greaves, Ian; Hunt, Paul (2010). "Ch. 5 Chemical Agents". Responding to Terrorism. A Medical Handbook. Elsevier. pp. 233–344. doi:10.1016/B978-0-08-045043-8.00005-2. ISBN978-0-08-045043-8. While arsine itself is odourless, its oxidation by air may produce a slight, garlic-like scent. However, it is lethal in concentrations far lower than those required to produce this smell.
^Bellama, J. M.; MacDiarmid, A. G. (1968). "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. 7 (10): 2070–2. doi:10.1021/ic50068a024.
^Scheele, Carl Wilhelm (1775) "Om Arsenik och dess syra"Archived 2016-01-05 at the Wayback Machine (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, ... )
^"Arsine" in Handbook of Preparative Inorganic Chemistry, 2nd ed., G. Brauer (ed.), Academic Press, 1963, NY, Vol. 1. p. 493.
^Herrmann, W. A.; Koumbouris, B.; Schaefer, A.; Zahn, T.; Ziegler, M. L. (1985). "Generation and Complex Stabilization of Arsinidene and Diarsine Fragments by Metal-Induced Degradation of Monoarsine". Chemische Berichte. 118 (6): 2472–88. doi:10.1002/cber.19851180624.
^King, E. J. (1959) Qualitative Analysis and Electrolytic Solutions Harcourt, Brace, and World; New York
^Atwood, D. A.; Cowley, A. H.; Harris, P. R.; Jones, R. A.; Koschmieder, S. U.; Nunn, C. M.; Atwood, J. L.; Bott, S. G. (1993). "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. 12: 24–29. doi:10.1021/om00025a010.
^R. Minkwitz, R.; Kornath, A.; Sawodny, W.; Härtner, H. (1994). "Über die Darstellung der Pnikogenoniumsalze AsH4+SbF6−, AsH4+AsF6−, SbH4+SbF6−". Zeitschrift für Anorganische und Allgemeine Chemie (in German). 620 (4): 753–756. doi:10.1002/zaac.19946200429.
