Cacodyl

Cacodyl
Ball and stick model of cacodyl	Space-filling model of cacodyl
Names
	Preferred IUPAC name Tetramethyldiarsane
	Other names Tetramethyldiarsenic(As—As); Bis(dimethylarsenic)(As—As); Tetramethyldiarsine
Identifiers
CAS Number	471-35-2 ;
3D model (JSmol)	Interactive image; Interactive image;
ChemSpider	71351 ;
ECHA InfoCard	100.006.766
EC Number	207-440-4;
PubChem CID	79018;
UNII	11N299093L ;
CompTox Dashboard (EPA)	DTXSID30197038 ;
	InChI InChI=1S/C4H12As2/c1-5(2)6(3)4/h1-4H3 Key: RSKPLCGMBWEANE-UHFFFAOYSA-N ; InChI=1/C4H12As2/c1-5(2)6(3)4/h1-4H3 Key: RSKPLCGMBWEANE-UHFFFAOYAG;
	SMILES [As]([As](C)C)(C)C; C[As](C)[As](C)C;
Properties
Chemical formula	C4H12As2
Molar mass	209.983 g·mol−1
Magnetic susceptibility (χ)	-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). verify (what is ?) Infobox references

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 is also the name of the functional group or radical (CH₃)₂As.

Preparation

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

History

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.

Applications

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.