Skatole or 3-methylindole is a mildly toxic white crystalline organic compound belonging to the indole family. It occurs naturally in feces (it is produced from tryptophan in the mammalian digestive tract) and coal tar and has a strong fecal odor. With the testicular steroid androstenone, skatole is regarded as a principal determinant of boar taint. It is also one of the molecules responsible for inducing bad breath, since it is produced by bacteria that feast on particles of food and tissue in the mouth. In low concentrations, it has a flowery smell and is found in several flowers and essential oils, including those of orange blossoms, jasmine, and Ziziphus mauritiana. It is used as a fragrance and fixative in many perfumes and as an aroma compound. Its name is derived from the Greek root skato- meaning "feces". Skatole was discovered in 1877 by the German physician Ludwig Brieger (1849–1919). Skatole is also used by U.S. military in its non-lethal weaponry; specifically, malodorants.
|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||131.178 g·mol−1|
|Appearance||White crystalline solid|
|Melting point||93 to 95 °C (199 to 203 °F; 366 to 368 K)|
|Boiling point||265 °C (509 °F; 538 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Skatole can be found as a white crystalline or fine powder solid, and it browns upon aging. It is nitrogenous, and one of the rings is a pyrrole. It is soluble in alcohol and benzene, and it gives a violet color in potassium ferrocyanide (K4Fe(CN)6·3H2O) and sulfuric acid (H2SO4). Skatole has a double ring system that displays aromaticity. It is continuous (all atoms in the ring are sp2 hybridized), planar, and follows the 4n+2 rule because it has 10 π electrons (n=2).
Skatole can be synthesized via the Fischer indole synthesis. Since it is one of the major byproducts of tryptophan through a catabolic pathway, it is also synthesized through the breakdown of tryptophan, and such process is facilitated by microorganisms.
Skatole is one of many compounds that are attractive to males of various species of orchid bees, which apparently gather the chemical to synthesize pheromones; it is commonly used as bait to attract and collect these bees for study. It is also known for being a chemical attractant for the Tasmanian grass grub beetle (Aphodius tasmaniae).
Skatole has been shown to be an attractant to gravid mosquitoes in both field and laboratory conditions. Because this compound is present in feces, it is found in combined sewage overflows (CSO) as streams and lakes containing CSO water have untreated human and industrial waste. Knowledge of this attractant makes CSO sites of particular interest when studying mosquito-borne diseases such as West Nile virus.
Skatole has been shown to cause pulmonary edema in goats, sheep, rats, and some strains of mice. It appears to selectively target club cells, which are the major site of cytochrome P450 enzymes in the lungs. These enzymes convert skatole to a reactive intermediate, 3-methyleneindolenine, which damages cells by forming protein adducts (see fog fever). A proper way to preserve the compound would be to store it inside tightly, sealed containers that are placed within a cool, dry place that is absent of heat and light.
Skatole is used as the starting material in the synthesis of atiprosin.
- Wesoly, R.; Weiler, U. "Nutritional Influences on Skatole Formation and Skatole Metabolism in the Pig". Retrieved 19 November 2019.
- Franklin, Deborah (1 May 2013). "To Beat Bad Breath, Keep the Bacteria in Your Mouth Happy". Retrieved 19 November 2019.
- Brieger, Ludwig (1877) "Ueber die flüchtigen Bestandtheile der menschlichen Excremente" ("On the volatile components of human excrement"), Berichte der deutschen chemischen Gesellschaft, 10 : 1027–1032.
- Reprinted in: Brieger, Ludwig (1878) "Ueber die flüchtigen Bestandtheile der menschlichen Excremente", Journal für Praktische Chemie, 17 : 124–138.
- See also: Brieger, Ludwig (1879) "Ueber Skatol" (On skatole), Berichte der deutschen chemischen Gesellschaft, 12 : 1985–1988.
Original : Ich habe mich zuerst mit der Untersuchung der flüchtigen Bestandtheile der Excremente aus sauerer Lösung beschäftigt. Es wurden dabei die flüchtigen Fettsäuren: Essigsäure, normale und Isobuttersäure, sowie die aromatischen Substanzen: Phenol, Indol und eine neue dem Indol verwandte Substanz, die ich Skatol nennen werde, erhalten.
Translation : I was occupied initially with the investigation of the volitile components of excrement in acidic solution. One obtained thereby volitile fatty acids; acetic acid; normal and isobutyric acid; as well as the aromatic substances: phenol, indole and a new substance which is related to indole and which I will name "skatole".; Brieger (1877), page 1030: Das Skatol ... (von το σχατος = faeces) ... (Skatole ... (from το σχατος = feces) ....)
- U.S. Patent 6,386,113
- Emil Fischer (1886) "Indole aus Phenylhydrazin" (Indole from phenylhydrazine), Annalen der Chemie, vol. 236, pages 126-151; for Fischer's synthesis of skatole, see page 137. (Fischer was not the first to prepare skatole. It was prepared, via other methods, in 1880 by von Baeyer, and in 1883 by Otto Fischer and German and by Fileti.)
- Whitehead, T. R.; Price, N. P.; Drake, H. L.; Cotta, M. A. (25 January 2008). "Catabolic pathway for the production of skatole and indoleacetic acid by the acetogen Clostridium drakei, Clostridium scatologenes, and swine manure". American Society for Microbiology:Applied and Environmental Microbiology. PMID 18223109. Retrieved 19 November 2019.
- Schiestl, F.P. & Roubik, D.W. (2004). "Odor Compound Detection in Male Euglossine Bees". Journal of Chemical Ecology. 29 (1): 253–257. doi:10.1023/A:1021932131526. PMID 12647866.
- Osborne, G. O.; Penman, D. R.; Chapman, R. B. (1975). "Attraction of Aphodius tasmaniae Hope to skatole". Australian Journal of Agricultural Research. 26(5): 839–841. Retrieved 19 November 2019.
- Beechler, J W., J G Miller, and M S Mulla (1994). "Field evaluation of synthetic compounds mediating oviposition in Culex mosquitoes (Diptera: Culicidae)". J Chem Ecol. 20 (2): 281–291. doi:10.1007/BF02064436.CS1 maint: multiple names: authors list (link)
- Miller, M; Kottler, S; Ramos-Vara, J; Johnson, P; Ganjam, V; Evans, T (2003). "3-Methylindole Induces Transient Olfactory Mucosal Injury in Ponies". Veterinary Pathology. 40 (4): 363–70. doi:10.1354/vp.40-4-363. PMID 12824507.
- "Skatole W301912". Sigma-Aldrich. Retrieved 19 November 2019.