Perchloromethyl mercaptan is the organosulfur compound with the formula CCl
3SCl. It is mainly used as an intermediate for the synthesis of dyes and fungicides (
captan
Captan is a general use pesticide (GUP) that belongs to the phthalimide class of fungicides. It is a white solid, although commercial samples appear yellow or brownish.
Applications
Although it can be applied on its own, Captan is often add ...
,
folpet
Folpet is the tradename for the organic compound with the formula C6H4(CO)2NSCCl3. It is a fungicide derived from phthalimide (C6H4(CO)2N-) and trichloromethylsulfenyl chloride. The compound is white although commercial samples can appear bro ...
). It is a colorless oil, although commercial samples are yellowish. It is insoluble in water but soluble in organic solvents. It has a foul, unbearable, acrid odor. Perchloromethyl mercaptan is the original name. The systematic name is trichloromethanesulfenyl chloride, because the compound is a
sulfenyl chloride, not a
mercaptan.
History
It was used as a
chemical warfare agent by the French in the 1915 battle of Champagne. Shortly thereafter, wartime use was abandoned due to the clear warning properties, the decomposition in the presence of iron and steel, and the easy removal of the vapor by charcoal.
[Sosnovsky, George "The chemistry of trichloromethanesulfenyl chloride" Chemical Reviews 1958, volume 58, 509-40. ]
Preparation
The method to prepare perchloromethyl mercaptan was first described by Rathke in 1873
and is still used.
Carbon disulfide
Carbon disulfide (also spelled as carbon disulphide) is a neurotoxic, colorless, volatile liquid with the formula and structure . The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical n ...
is chlorinated using an iodine catalyst. The following equations operate most efficiently at temperatures below about 30 °C
:CS
2 + 3 Cl
2 → CCl
3SCl + SCl
2
:2 CS
2 + 5 Cl
2 → 2 CCl
3SCl + S
2Cl
2
At higher temperatures, the chlorination gives
carbon tetrachloride and additional sulfur chlorides.
[Manchiu D. S. Lay, Mitchell W. Sauerhoff And Donald R. Saunders "Carbon Disulfide" in Ullmann's Encyclopedia Of Industrial Chemistry, 2000, Wiley-VCH, Weinheim.
] The formation of byproducts can be suppressed by performing the reaction in the presence of
diketone
In organic chemistry, a dicarbonyl is a molecule containing two carbonyl () groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls ...
s.
[Greco, C., (1978), Production of perchloromethyl mercaptan, Stauffer ChemicalCompany, Westport, Conn.] Another byproduct is
thiophosgene
Thiophosgene is a red liquid with the formula . It is a molecule with trigonal planar geometry. There are two reactive C–Cl bonds that allow it to be used in diverse organic syntheses.
Preparation
is prepared in a two-step process from carbon ...
. The more volatile byproducts such as carbon tetrachloride and
sulfur dichloride can be removed by
distillation
Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heat ...
. The separation of perchloromethyl mercaptan from S
2Cl
2 by distillation is challenging since their
boiling points
The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor.
The boiling point of a liquid varies depending upon the surrounding envir ...
are very close. Another byproduct that forms is
hexachloroethane
Hexachloroethane, also known as perchloroethane is the organochlorine compound with the chemical formula . It is white solid at room temperature with a camphor-like odor. It has been used by the military in smoke compositions, such as base-eject ...
. Innovations in the basic Rathke method have been reported.
Reactivity
The compound slowly hydrolyzes:
:CSCl
4 + 2 H
2O → CO
2 + 4 HCl + S
8
The compound is corrosive to most metals. It reacts with iron, evolving carbon tetrachloride. Perchloromethyl mercaptan is oxidized by nitric acid to trichloromethanesulfonyl chloride (Cl
3CSO
2Cl), a white solid.
Toxicity
When it is heated or in a fire, it will emit toxic and corrosive gases. It is also very toxic by inhalation or skin absorption.
[Committee on Acute Exposure Guideline Levels, Committee on Toxicology, National Research Council, (2011), Acute Exposure Guideline Levels for Selected Airborne Chemicals.]
At least two mechanisms could account for the toxicity of perchloromethyl mercaptan, as hypothesized by Althoff (1973). The first mechanism is a reaction between perchloromethyl mercaptan and biological functional groups such as hydroxyl, sulfhydryl, amino and carboxyl groups. This results in an inactivation of key enzymes. A second general pathway reaction is the hydrolysis to give hydrochloric acid.
References
External links
CDC - NIOSH Pocket Guide to Chemical Hazards
{{Chemical agents
Organosulfur compounds
Trichloromethyl compounds
Pulmonary agents
Foul-smelling chemicals