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 betwe ...

(CH₃)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; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

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- ...

s industry, a building block to other

organoarsenic compound Organoarsenic chemistry is the chemistry of Chemical compound, compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herb ...

s, and serves as a ligand in

coordination chemistry A coordination complex is a chemical compound consisting of a central atom or ion, which is usually metallic and is called the ''coordination centre'', and a surrounding array of chemical bond, bound molecules or ions, that are in turn known as ' ...

. It has distinct "

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plants in the genus '' Allium''. Its close relatives include the onion, shallot, leek, chives, Welsh onion, and Chinese onion. Garlic is native to central and south Asia, str ...

"-like smell. Trimethylarsine had been discovered as early as 1854.

Structure and preparation

AsMe₃ 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 unstab ...

with

trimethylaluminium Trimethylaluminium or TMA is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula (abbreviated as , where Me stands for methyl), as it exists as a dimer. This colorless liquid is pyrophoric. It is an ...

: :As₂O₃ + 1.5 lMe₃sub>2 → 2 AsMe₃ + 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 , , '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 organolithium compounds and triethylb ...

due to the exothermic nature of the following reaction, which initiates combustion: :AsMe₃ + 1/2 O₂ → OAsMe₃ (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 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 pla ...

'' produces significant amounts of methyl arsines via methylation of arsenic-containing inorganic

pigment A pigment is a powder used to add or alter color or change visual appearance. Pigments are completely or nearly solubility, insoluble and reactivity (chemistry), chemically unreactive in water or another medium; in contrast, dyes are colored sub ...

s, especially

Paris green Paris green (copper(II) acetate triarsenite or copper(II) acetoarsenite) is an arsenic-based organic pigment. As a green pigment it is also known as Mitis green, Schweinfurt green, Sattler green, emerald, Vienna green, Emperor green or Mount ...

and Scheele's Green, 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 Methyl compounds