Trimethylarsine
Encyclopedia
Trimethylarsine is the chemical compound
with the formula
(CH3)3As, commonly abbreviated AsMe3 or TMAs. This organic derivative of arsine
has been used as a source of arsenic
in microelectronics industry, a building block to other organoarsenic compound
s, and serves as a ligand in coordination chemistry. It has distinct "garlic
"-like smell. Trimethylarsine had been discovered as early as 1854.
, AsMe3 is a pyramidal molecule. The As-C distances average 1.519 Å, and the C-As-C angles are 91.83° This bond angle is a strong indication of a low, if any, hybridisation
of the atomic orbital
s, leaving the lone pair in the s-orbital buried in the inner regions of the arsenic atom, rather than pointing outward like the lone pair of the ammonia molecule.
Trimethylarsine can be prepared by treatment of arsenic oxide
with trimethylaluminium
:
due to the exothermic nature of the following reaction, which initiates combustion:
s, especially Paris green
and Scheele's Green
, which were once used in indoor wallpapers. Newer studies show that trimethylearsine has a low toxicity and could therefore not account for the death and the severe health problems observed in the 19th century.
from Germany, Canada, and the U.S.A., and is the major arsenic-containing compound in the gas.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
(CH3)3As, commonly abbreviated AsMe3 or TMAs. This organic derivative of arsine
Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...
has been used as a source of arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
in microelectronics industry, a building block to other organoarsenic compound
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 fungicides. In general these applications are declining in...
s, and serves as a ligand in coordination chemistry. It has distinct "garlic
Garlic
Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...
"-like smell. Trimethylarsine had been discovered as early as 1854.
Structure and Preparation
As predicted by VSEPR theoryVSEPR theory
Valence shell electron pair repulsion theory is a model in chemistry used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion. It is also named Gillespie–Nyholm theory after its two main developers...
, AsMe3 is a pyramidal molecule. The As-C distances average 1.519 Å, and the C-As-C angles are 91.83° This bond angle is a strong indication of a low, if any, hybridisation
Hybridisation
Hybridisation or hybridization may refer to:*The process of combining different varieties or species of organisms to create a hybrid *Nucleic acid hybridisation, the process of joining two complementary strands of DNA...
of the atomic orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...
s, leaving the lone pair in the s-orbital buried in the inner regions of the arsenic atom, rather than pointing outward like the lone pair of the ammonia molecule.
Trimethylarsine can be prepared by treatment of arsenic oxide
Arsenic trioxide
Arsenic trioxide is the inorganic compound with the formula As2O3. This commercially important oxide of arsenic is the main precursor to other arsenic compounds, including organoarsenic compounds. Approximately 50,000 tonnes are produced annually...
with trimethylaluminium
Trimethylaluminium
Trimethylaluminium is the chemical compound with the formula Al26, abbreviated as Al2Me6, 2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound...
:
- As2O3 + 1.5 [AlMe3]2 → 2 AsMe3 + 3/n (MeAl-O)n
Properties and reactions
Trimethylarsine is pyrophoricPyrophoricity
A pyrophoric substance is a substance that will ignite spontaneously in air. Examples are iron sulfide and many reactive metals including uranium, when powdered or sliced thin. Pyrophoric materials are often water-reactive as well and will ignite when they contact water or humid air...
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 micobes 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 Scopulariopsis brevicaulis produces significant amounts of methyl arsines via methylation of arsenic-containing inorganic pigmentPigment
A pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s, especially Paris green
Paris Green
Paris Green is an inorganic compound more precisely known as copper acetoarsenite. It is a highly toxic emerald-green crystalline powder that has been used as a rodenticide and insecticide, and also as a pigment, despite its toxicity. It is also used as a blue colorant for fireworks...
and Scheele's Green
Scheele's Green
Scheele's Green, also called Schloss Green, is chemically a cupric hydrogen arsenite , CuHAsO3. It is a compound similar to Paris Green...
, which were once used in indoor wallpapers. Newer studies show that trimethylearsine has a low toxicity and could therefore not account for the death and the severe health problems observed in the 19th century.
Importance
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 gasLandfill gas
Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill.-Production:Landfill gas production results from chemical reactions and microbes acting upon the waste as the putrescible materials begins to break down in the landfill...
from Germany, Canada, and the U.S.A., and is the major arsenic-containing compound in the gas.