Trimethylarsine (abbreviated TMA or TMAs) is the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
(CH
3)
3As, commonly abbreviated As
Me3 or TMAs. This organic derivative of
arsine
Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. 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 th ...
has been used as a source of
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but ...
in
microelectronic
Microelectronics is a subfield of electronics. As the name suggests, microelectronics relates to the study and manufacture (or microfabrication) of very small electronic designs and components. Usually, but not always, this means micrometre-sc ...
s industry, a building block to other
organoarsenic compound
Organoarsenic chemistry is the chemistry of compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herbicides, and fungic ...
s, and serves as a ligand in
coordination chemistry
A coordination complex consists of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of bound molecules or ions, that are in turn known as ''ligands'' or complexing agents. Many ...
. It has distinct "
garlic
Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...
"-like smell. Trimethylarsine had been discovered as early as 1854.
Structure and preparation
AsMe
3 is a pyramidal molecule. The As-C distances average 1.519 Å, and the C-As-C angles are 91.83°
Trimethylarsine can be prepared by treatment of
arsenic oxide Arsenic oxide may refer to any of the following:
*Arsenic dioxide, As2O4
*Arsenic trioxide, As2O3
*Arsenic pentoxide
Arsenic pentoxide is the inorganic compound with the formula As2O5. This glassy, white, deliquescent solid is relatively unstabl ...
with
trimethylaluminium
Trimethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( CH3)6 (abbreviated as Al2Me6 or TMA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industriall ...
:
:As
2O
3 + 1.5
lMe3sub>2 → 2 AsMe
3 + 3/n (MeAl-O)
n
Occurrence and reactions
Trimethylarsine is the volatile byproduct of microbial action on inorganic forms of arsenic which are naturally occurring in rocks and soils at the parts-per-million level. Trimethylarsine has been reported only at trace levels (parts per billion) in
landfill gas
Landfill gas is a mix of different gases created by the action of microorganisms within a landfill as they decompose organic waste, including for example, food waste and paper waste. Landfill gas is approximately forty to sixty percent methane, ...
from Germany, Canada, and the U.S.A., and is the major arsenic-containing compound in the gas.
Trimethylarsine is
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
due to the exothermic nature of the following reaction, which initiates combustion:
:AsMe
3 + 1/2 O
2 → OAsMe
3 (TMAO)
History
Poisoning events due to a gas produced by certain microbes was assumed to be associated with the arsenic in paint. In 1893 the Italian physician
Bartolomeo Gosio
Bartolomeo Gosio (17 March 1863 – 13 April 1944) was an Italian medical scientist. He discovered a toxic fume, eponymously named "Gosio gas", which is produced by microorganisms, that killed many people. He identified the chemical nature of the g ...
published his results on "Gosio gas" that was subsequently shown to contain trimethylarsine. Under wet conditions, the mold ''
Microascus brevicaulis
''Microascus brevicaulis'' is a microfungus in the Ascomycota. It is the teleomorph form of ''Scopulariopsis brevicaulis.'' ''Microascus brevicaulis'' occurs world-wide as a saprotroph in soil, a common agent of biodeterioration, an irregular p ...
'' produces significant amounts of methyl arsines via methylation of arsenic-containing inorganic
pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...
s, especially
Paris green and
Scheele's Green
Scheele's Green, also called Schloss Green, is chemically a cupric hydrogen arsenite (also called copper arsenite or acidic copper arsenite), . It is chemically related to Paris Green. Scheele's Green was invented in 1775 by Carl Wilhelm Schee ...
, which were once used in indoor wallpapers. Newer studies show that trimethylarsine has a low toxicity and could therefore not account for the death and the severe health problems observed in the 19th century.
Safety
Trimethylarsine is potentially hazardous,
although its toxicity is often overstated.
[
]
References
{{Reflist, 30em
External links
Index by Molecular FormulaMicrobial Methylation of Metalloids: Arsenic, Antimony, and Bismuth
Organoarsenic compounds
Foul-smelling chemicals