Cacodyl, also known as dicacodyl or tetramethyldiarsine, (CH
3)
2As–As(CH
3)
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
Spontaneous combustion or spontaneous ignition is a type of combustion which occurs by self-heating (increase in temperature due to exothermic internal reactions), followed by thermal runaway (self heating which rapidly accelerates to high tem ...
in dry air.
Cacodyl is also the name of the
functional group
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the res ...
or
radical (CH
3)
2As.
Preparation
A mixture of dicacodyl and cacodyl oxide ((CH
3)
2As–O–As(CH
3)
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:
:
A more efficient synthesis was later developed which started from the dimethyl arsine chloride and dimethyl arsine:
:
History
Robert Wilhelm Bunsen coined the name kakodyl (later modified to cacodyl in English) for the dimethylarsinyl radical, (CH
3)
2As, from the Greek ''κακώδης kakōdēs'' ("evil-smelling") and ὕλη ''hylē'' ("matter").
It was investigated by
Edward Frankland and (for over six years) by
Robert Bunsen and is considered the earliest
organometallic
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and ...
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
Baron Jöns Jacob Berzelius (; by himself and his contemporaries named only Jacob Berzelius, 20 August 1779 – 7 August 1848) was a Swedish chemist. Berzelius is considered, along with Robert Boyle, John Dalton, and Antoine Lavoisier, to be ...
, which resulted in a wide use of cacodyl in research laboratories. Afterward interest in the toxic, malodorous compound decreased. During
World War I
World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
the use of cacodyl as a
chemical weapon
A chemical weapon (CW) is a specialized munition that uses chemicals formulated to inflict death or harm on humans. According to the Organisation for the Prohibition of Chemical Weapons (OPCW), this can be any chemical compound intended as ...
was considered, but it was never used in the war. Inorganic chemists discovered the properties of cacodyl as a
ligand
In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's ele ...
for transition metals.
See also
*
Cacodylic acid
Cacodylic acid is an organoarsenic compound with the formula (CH3)2 AsO2H. With the formula R2As(O)OH, it is the simplest of the arsinic acids. It is a colorless solid that is soluble in water.
Neutralization of cacodylic acid with base gives ...
*
Dimethyl(trifluoromethylthio)arsine
*
Lewisite
Lewisite (L) (A-243) is an organoarsenic compound. It was once manufactured in the U.S., Japan, Germany and the Soviet Union for use as a Chemical warfare, chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although the substa ...
*
Trimethylarsine
*
Cacodyl cyanide
*
Cacodyl oxide
References
*{{cite journal
, title = The Crystal Structure of Arsenomethane
, author = John H. Burns and Jürg Waser
, journal = J. Am. Chem. Soc.
, year = 1957
, volume = 79
, issue = 4
, pages = 859–864
, doi = 10.1021/ja01561a020
, hdl = 1911/18207
, url = https://scholarship.rice.edu/bitstream/1911/18207/1/3079641.PDF
, hdl-access = free
Foul-smelling chemicals