Cacodyl, also known as dicacodyl or tetramethyldiarsine, (CH₃)₂As–As(CH₃)₂, is an

organoarsenic Organoarsenic chemistry is the chemistry of compounds containing a chemical bond between arsenic and carbon. A few organoarsenic compounds, also called "organoarsenicals," are produced industrially with uses as insecticides, herbicides, and ...

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 te ...

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 r ...

radical Radical may refer to: Politics and ideology Politics * Radical politics, the political intent of fundamental societal change *Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe an ...

(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 Potassium acetate (CH3COOK) is the potassium salt of acetic acid. It is a hygroscopic solid at room temperature. Preparation It can be prepared by treating a potassium-containing base such as potassium hydroxide or potassium carbonate with acetic ...

with

arsenic trioxide Arsenic trioxide, sold under the brand name Trisenox among others, is an inorganic compound and medication. As an industrial chemical, whose major uses include in the manufacture of wood preservatives, pesticides, and glass. As a medication, it ...

. 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 Robert Wilhelm Eberhard Bunsen (; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. The Buns ...

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"). It was investigated by

Edward Frankland Sir Edward Frankland, (18 January 18259 August 1899) was an English chemist. He was one of the originators of organometallic chemistry and introduced the concept of combining power or valence. An expert in water quality and analysis, he was ...

and (for over six years) by

Robert Bunsen Robert Wilhelm Eberhard Bunsen (; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. The Bu ...

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 s ...

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 o ...

, 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 a ...

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 elect ...

for transition metals.

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

Preparation

History

Applications

See also

References