What molecule am I?
Thioacetone is the simplest thioketone but very different from its cousin acetone1 (Molecule of the Week for April 9, 2012). Whereas acetone is stable, miscible with water, and a useful solvent, thioacetone is unstable above –20 ºC, essentially insoluble in water, and of no practical value.
Thioacetone’s main claim to “fame” is its extraordinarily foul odor. Its smell is even worse than those of familiar small sulfur-containing molecules such as methanethiol2, ethanethiol3, and 1-butanethiol4.
At ambient temperature, thioacetone reacts with itself to form cyclic trithioacetone (see fast facts table) and thioacetone polymers. In 1889, Eugen Baumann* and E. Fromm at the University of Freiburg (Germany) synthesized trithioacetone via the reaction between hydrogen sulfide and acetone. They also obtained a small amount of monomeric thioacetone, which can be fully recovered from the trimer by heating it to >500 ºC. The liquid trimer is almost as foul-smelling as the monomer5.
Much has been written about thioacetone’s evil odor. In 2009, Derek Lowe, a writer for Science, labeled the molecule as one of the “Things I Won’t Work With”. Among his comments:
. . . [it] makes no noise and leaves no wreckage. It merely stinks. But it does so relentlessly and unbearably. It makes innocent downwind pedestrians stagger, clutch their stomachs, and flee in terror. It reeks to a degree that makes people suspect evil supernatural forces.
Eight years later, Ross Pomeroy at Real Clear Science wrote “The Dangerous Stink of the World's Smelliest Chemical”. He cited the 1889 experience of Baumann and Fromm, in which the smell of thioacetone/trithioacetone spread all over Freiburg, causing fainting, vomiting, and a panicked evacuation among the residents. A similar event occurred in 1967, when researchers at Esso Petroleum (Abingdon, UK) worked with the compounds. A 2020 post by Grayson Van Beuren in The Paratext Blog covered much of the same ground.
This Halloween, if you’re looking for ways to haunt your neighborhood, don’t—we repeat, don’t—even think about making thioacetone in your basement.
1. CAS Reg. No. 67-64-1.
2. CAS Reg. No. 74-93-1.
3. CAS Reg. No. 75-08-1.
4. CAS Reg. No. 109-79-5.
5. See the hazard information table for trithioacetone. Note that thioacetone is too unstable to measure its hazardous properties.
Trithioacetone hazard information*
| Hazard class** | GHS code and hazard statement | |
|---|---|---|
| Skin corrosion/irritation, category 2 | H315—Causes skin irritation |  |
| Serious eye damage/eye irritation, category 2A | H319—Causes serious eye irritation | |
| Specific target organ toxicity, single exposure, respiratory system, category 3 | H335—May cause respiratory irritation | |
| Specific target organ toxicity, repeated exposure, category 1 | H372—Causes damage to organs through prolonged or repeated exposure |  |
| Long-term (acute) aquatic hazard, category 1 | H410—Very toxic to aquatic life with long-lasting effects |  |
*Compilation of multiple safety data sheets.
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Explanation of pictograms.
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Thioacetone fast facts
| CAS Reg. No. | 4756-05-2 |
| SciFindern name | 2-Propanethione |
| Empirical formula | C3H6S |
| Molar mass | 74.14 g/mol |
| Appearance | Orange to brown liquid |
| Boiling point | 68–70 °C |
| Water solubility | ≈3 g/L |
Trithioacetone fast facts
| CAS Reg. No. | 828-26-2 |
| SciFindern name | 1,3,5-Trithiane, 2,2,4,4,6,6-hexamethyl- |
| Empirical formula | C9H18S3 |
| Molar mass | 222.44 g/mol |
| Appearance | Colorless to yellow liquid |
| Melting point | 24 °C |
| Boiling point | 105–107 °C (10 torr) |
| Water solubility | 16 mg/L |
Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.
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