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Structural formula of cacodyl
Ball and stick model of cacodyl
IUPAC name
Other names
471-35-2 YesY
ChemSpider 71351 YesY
EC Number 207-440-4
Jmol 3D model Interactive image
Interactive image
PubChem 79018
Molar mass 209.98 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Cacodyl, dicacodyl, tetramethyldiarsine, alkarsine or minor part of the "Cadet's fuming liquid" (after the French chemist Louis Claude Cadet de Gassicourt) (CH3)2As—As(CH3)2 is a poisonous oily liquid with a garlicky odor. Cacodyl undergoes spontaneous combustion in dry air.


Cacodyl oxide is prepared by the reaction of potassium acetate with arsenic trioxide.

4 CH3CO2K + As2O3 → As2(CH3)4 + 2 K2CO3 + 2 CO2

A subsequent reduction or disproportionation of the substance under the reaction conditions yields a mixture of several methylated arsenic compounds.

A far better synthesis was developed which started from the dimethyl arsine chloride and dimethyl arsine.

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


Jöns Jakob Berzelius coined the name kakodyl (later changed to cacodyl) for the dimethylarsinyl radical, (CH3)2As, from the Greek kakodes (evil-smelling) and hyle (matter).[1]

It was investigated by Edward Frankland and Robert Bunsen and is considered one of the earliest organometallic compounds ever discovered. It was originally made from arsenic distilled with potassium acetate.

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.


Cacodyl was used to prove the radical theory of Berzelius, which resulted in a wide use of cacodyl in research laboratories. After the radical theory was established, the interest in the toxic substance with the awful smell decreased. During World War I the use of cacodyl as poison gas was considered, but it was never used in the war. The inorganic chemists discovered the properties of cacodyl as a ligand for transition metals.


  1. ^ Berzelius, J. J. (1839). Jahresberichte über die Fortschritte der physischen Wissenschaften. 18: 487.  Missing or empty |title= (help)