Arsine
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". General properties 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 0.5ppm. 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. Similar to stibine, the decomposition of arsine is autocatalytic, as the arsenic freed during the reaction acts as a catalyst for the same reaction. Several other factors, such as humidity, presence of light and certain catalysts (namely alumina) facilitate the rate of decomposition. 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. Discovery and synthesis AsH3 is generally prepared by the reaction of As3+ sources with H− equivalents. 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. 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: 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, AsH3 is stable kinetically but not thermodynamically. 2 AsH3 → 3 H2 + 2 As This decomposition reaction is the basis of the Marsh test, which detects the elemental As. Oxidation 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 Arsine will react violently in presence of strong oxidizing agents, such as potassium permanganate, sodium hypochlorite, or nitric acid. Precursor to metallic derivatives 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. Gutzeit test A characteristic