Trimethylarsine (abbreviated TMA or TMAs) 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,[1] a building block to other organoarsenic compounds, and serves as a ligand in coordination chemistry. It has distinct "garlic"-like smell. Trimethylarsine had been discovered as early as 1854.

Structural formula of trimethylarsine with an implicit electron pair
Ball and stick model of trimethylarsine
Preferred IUPAC name
Other names
  • Gosio gas
  • Trimethanidoarsenic
3D model (JSmol)
ECHA InfoCard 100.008.925 Edit this at Wikidata
EC Number
  • 209-815-8
MeSH Trimethylarsine
RTECS number
  • CH8800000
  • InChI=1S/C3H9As/c1-4(2)3/h1-3H3 checkY
  • InChI=1/C3H9As/c1-4(2)3/h1-3H3
  • [As](C)(C)C
  • C[As](C)C
Molar mass 120.027 g·mol−1
Appearance Colourless liquid
Density 1.124 g cm−3
Melting point −87.3 °C (−125.1 °F; 185.8 K)
Boiling point 56 °C (133 °F; 329 K)
Slightly soluble
Solubility in other solvents organic solvents
Trigonal pyramidal
0.86 D
Occupational safety and health (OHS/OSH):
Main hazards
GHS labelling:
GHS06: ToxicGHS09: Environmental hazard
H301, H331, H410
Flash point −25 °C (−13 °F; 248 K)
Safety data sheet (SDS) External MSDS
Related compounds
Related compounds
Cacodylic acid
Supplementary data page
Trimethylarsine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Structure and preparationEdit

AsMe3 is a pyramidal molecule. The As-C distances average 1.519 Å, and the C-As-C angles are 91.83°[2]

Trimethylarsine can be prepared by treatment of arsenic oxide with trimethylaluminium:[3]

As2O3 + 1.5 [AlMe3]2 → 2 AsMe3 + 3/n (MeAl-O)n

Occurrence and reactionsEdit

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.[4] Trimethylarsine has been reported only at trace levels (parts per billion) in landfill gas from Germany, Canada, and the U.S.A., and is the major arsenic-containing compound in the gas.[5][6][7]

Trimethylarsine is pyrophoric due to the exothermic nature of the following reaction, which initiates combustion:

AsMe3 + 1/2 O2 → OAsMe3 (TMAO)


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.[8] Under wet conditions, the mold Microascus brevicaulis produces significant amounts of methyl arsines via methylation[9] of arsenic-containing inorganic pigments, especially Paris green 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.[10][11]


Trimethylarsine is potentially hazardous,[12][13][14] although its toxicity is often overstated.[10]


  1. ^ Hoshino, Masataka (1991). "A mass spectrometric study of the decomposition of trimethylarsine (TMAs) with triethylgallium (TEGa)". Journal of Crystal Growth. 110 (4): 704–712. Bibcode:1991JCrGr.110..704H. doi:10.1016/0022-0248(91)90627-H.
  2. ^ Wells, A.F. (1984). Structural Inorganic Chemistry, fifth edition. Oxford University Press. ISBN 978-0-19-855370-0.
  3. ^ V. V. Gavrilenko, L. A. Chekulaeva, and I. V. Pisareva, "Highly efficient synthesis of trimethylarsine" Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2122–2123, 1996.
  4. ^ Cullen, W.R., Reimer, K.J. (1989). "Arsenic speciation in the environment". Chem. Rev. 89 (4): 713–764. doi:10.1021/cr00094a002. hdl:10214/2162.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  5. ^ Feldmann, J., Cullen, W.R. (1997). "Occurrence of Volatile Transition Metal Compounds in Landfill Gas: Synthesis of Molybdenum and Tungsten Carbonyls in the". Environ. Sci. Technol. 31 (7): 2125–2129. doi:10.1021/es960952y.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ Pinel-Raffaitin, P., LeHecho, I., Amouroux, D., Potin-Gautier, M. (2007). "Distribution and Fate of Inorganic and Organic Arsenic Species in Landfill Leachates and Biogases". Environ. Sci. Technol. 41 (13): 4536–4541. Bibcode:2007EnST...41.4536P. doi:10.1021/es0628506. PMID 17695893.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  7. ^ Khoury, J.T.; et al. (April 7, 2008). "Analysis of Volatile Arsenic Compounds in Landfill Gas". Odors & Air Emissions 2008. Phoenix, Arizona: Water Environment Federation.
  8. ^ Frederick Challenger (1955). "Biological methylation". Q. Rev. Chem. Soc. 9 (3): 255–286. doi:10.1039/QR9550900255.
  9. ^ Ronald Bentley & Thomas G. Chasteen (2002). "Microbial Methylation of Metalloids: Arsenic, Antimony, and Bismuth". Microbiology and Molecular Biology Reviews. 66 (2): 250–271. doi:10.1128/MMBR.66.2.250-271.2002. PMC 120786. PMID 12040126.
  10. ^ a b William R. Cullen; Ronald Bentley (2005). "The toxicity of trimethylarsine: an urban myth". J. Environ. Monit. 7 (1): 11–15. doi:10.1039/b413752n. PMID 15693178.
  11. ^ Frederick Challenger; Constance Higginbottom; Louis Ellis (1933). "The formation of organo-metalloidal compounds by microorganisms. Part I. Trimethylarsine and dimethylethylarsine". J. Chem. Soc.: 95–101. doi:10.1039/JR9330000095.
  12. ^ Andrewes, Paul; et al. (2003). "Dimethylarsine and Trimethylarsine Are Potent Genotoxins In Vitro". Chem. Res. Toxicol. 16 (8): 994–1003. doi:10.1021/tx034063h. PMID 12924927.
  13. ^ Irvin, T.Rick; et al. (1995). "In-vitro Prenatal Toxicity of Trimethylarsine, Trimethylarsine Oxide and Trimethylarsine Sulfide". Applied Organometallic Chemistry. 9 (4): 315–321. doi:10.1002/aoc.590090404.
  14. ^ Hiroshi Yamauchi; Toshikazu Kaise; Keiko Takahashi; Yukio Yamamura (1990). "Toxicity and metabolism of trimethylarsine in mice and hamsters". Fundamental and Applied Toxicology. 14 (2): 399–407. doi:10.1016/0272-0590(90)90219-A. PMID 2318361.

External linksEdit