Thioacetone

Thioacetone is an organosulfur compound belonging to the -thione group called thioketones with a chemical formula (CH3)2CS. It is an unstable orange or brown substance that can be isolated only at low temperatures. Above , thioacetone readily converts to a polymer and a trimer, trithioacetone. It has an extremely potent, unpleasant odor, and is considered one of the worst-smelling chemicals known to humanity.
Thioacetone was first obtained in 1889 by Baumann and Fromm, as a minor impurity in their synthesis of trithioacetone.
Preparation
Thioacetone is usually obtained by cracking the cyclic trimer trithioacetone, [(CH3)2CS]3. The trimer is prepared by pyrolysis of allyl isopropyl sulfide or by treating acetone with hydrogen sulfide in the presence of a Lewis acid. The trimer cracks at to give the thione.
Polymerization
Unlike its oxygen analogue acetone, which does not polymerise easily, thioacetone spontaneously polymerizes even at very low temperatures, pure or dissolved in ether or ethylene oxide, yielding a white solid that is a varying mixture of a linear polymer and the cyclic trimer trithioacetone. Infrared absorption of this product occurs mainly at 2950, 2900, 1440, 1150, 1360, and 1375 cm−1 due to the geminal methyl pairs, and at 1085 and 643 cm−1 due to the C–S bond. The 1H NMR spectra shows a single peak at x = 8.1.
The mean molecular weight of the polymer varies from 2000 to 14000 depending on the preparation method, temperature, and presence of the thioenol tautomer. The polymer melts in the range of about 70 °C to 125 °C. Polymerization is promoted by free radicals and light.
The cyclic trimer of thioacetone (trithioacetone) is a white or colorless compound with a melting point of , near room temperature. It also has a disagreeable odor.
Odor
Thioacetone has an intensely foul odour. Like many low molecular weight organosulfur compounds, the smell is potent and can be detected even when highly diluted. In 1889, an attempt to distill the chemical in the German city of Freiburg was followed by cases of vomiting, nausea, and unconsciousness in an area with a radius of around the laboratory due to the smell. In an 1890 report, British chemists at the Whitehall Soap Works in Leeds noted that dilution seemed to make the smell worse and described the smell as "fearful".
In 1967, Esso researchers repeated the experiment of cracking trithioacetone at a laboratory south of Oxford, UK. They reported their experience as follows:
Thioacetone is sometimes considered a dangerous chemical due to its extremely foul odor and its supposed ability to render people unconscious, induce vomiting, and be detected over long distances. As of 2023, at least two YouTube scientists (Nigel of "NileRed" and Zach of "LabCoatz") have published videos showing themselves smelling freshly-prepared thioacetone, both up-close and from a distance. In both cases, the individuals did not experience previously described side effects (nausea, vomiting, or unconsciousness). The cameraman filming NileReds video however was not able to tolerate the smell.
See also
Thiobenzophenone, a thioketone that can be isolated as a solid
Bromoacetone
Chloroacetone
Fluoroacetone
Iodoacetone
References
External links
Thioacetone, NIST
Trithioacetone, Aldrich
Thioketones
Foul-smelling chemicals