Cacodyl, also known as dicacodyl or tetramethyldiarsine, (CH3)2As–As(CH3)2, is an organoarsenic compound that constitutes a major part of "Cadet's fuming liquid" (named after the French chemist Louis Claude Cadet de Gassicourt). It is a poisonous oily liquid with an extremely unpleasant garlicky odor. Cacodyl undergoes spontaneous combustion in dry air.[1]

Cacodyl
Structural formula of cacodyl
Ball and stick model of cacodyl
Names
Preferred IUPAC name
Tetramethyldiarsane
Other names
Tetramethyldiarsenic(AsAs)

Bis(dimethylarsenic)(AsAs)

Tetramethyldiarsine
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.006.766 Edit this at Wikidata
EC Number
  • 207-440-4
UNII
  • InChI=1S/C4H12As2/c1-5(2)6(3)4/h1-4H3 checkY
    Key: RSKPLCGMBWEANE-UHFFFAOYSA-N checkY
  • InChI=1/C4H12As2/c1-5(2)6(3)4/h1-4H3
    Key: RSKPLCGMBWEANE-UHFFFAOYAG
  • [As]([As](C)C)(C)C
  • C[As](C)[As](C)C
Properties
C4H12As2
Molar mass 209.983 g·mol−1
-99.9·10−6 cm3/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Cacodyl is also the name of the functional group or radical (CH3)2As.

PreparationEdit

A mixture of dicacodyl and cacodyl oxide ((CH3)2As–O–As(CH3)2) was first prepared by Cadet by the reaction of potassium acetate with arsenic trioxide. A subsequent reduction yields a mixture of several methylated arsenic compounds including dicacodyl.

The global reaction (mass balance) corresponding to the oxide formation is the following:

4 CH3COOK + As2O3 → ((CH3)2As)2O + 2 K2CO3 + 2 CO2

A more efficient synthesis was later developed which started from the dimethyl arsine chloride and dimethyl arsine:

As(CH3)2Cl + As(CH3)2H → As2(CH3)4 + HCl

HistoryEdit

Robert Wilhelm Bunsen coined the name kakodyl (later modified to cacodyl in English) for the dimethylarsinyl radical, (CH3)2As, from the Greek κακώδης kakōdēs ("evil-smelling") and ὕλη hylē ("matter").[2]

It was investigated by Edward Frankland and (for over six years) by Robert Bunsen and is considered the earliest organometallic compound ever discovered (even though arsenic is not a true metal).

From it other compounds were made, such as cacodyl fluoride, cacodyl chloride, et cetera. One compound, cacodyl cyanide, was particularly awful. In Bunsen's words "the smell of this body produces instantaneous tingling of the hands and feet, and even giddiness and insensibility...It is remarkable that when one is exposed to the smell of these compounds the tongue becomes covered with a black coating, even when no further evil effects are noticeable".

Work on cacodyl led Bunsen to the postulation of "methyl radicals" as part of the then-current radical theory.

ApplicationsEdit

Cacodyl was used to try to prove the radical theory of Jöns Jacob Berzelius, which resulted in a wide use of cacodyl in research laboratories. Afterward interest in the toxic, malodorous compound decreased. During World War I the use of cacodyl as a chemical weapon was considered, but it was never used in the war. Inorganic chemists discovered the properties of cacodyl as a ligand for transition metals.

See alsoEdit

ReferencesEdit

  1. ^ Seyferth, Dietmar (2001). "Cadet's Fuming Arsenical Liquid and the Cacodyl Compounds of Bunsen". Organometallics. 20 (8): 1488–1498. doi:10.1021/om0101947.
  2. ^ Berzelius, Jöns Jacob (1841). "Kakodyl". Jahresberichte über die Fortschritte der Physischen Wissenschaften. 20: 526–539.