Skatole or 3-methylindole is a mildly toxic white crystalline organic compound with chemical formula C9H9N and CAS number 83-34-1. The compound belongs to the indole family and has a methyl substituent in position 3 of the indole ring. It occurs naturally in feces (it is produced from tryptophan in the mammalian digestive tract), beets, and coal tar, and has a strong fecal odor. In low concentrations it has a flowery smell and is found in several flowers and essential oils, including those of orange blossoms, jasmine, and Zizyphus mauritania. It is used as a fragrance and fixative in many perfumes and as an aroma compound. Its name is derived from skato, the Greek word for dung.
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. This is probably the reason it's so foul smelling. It is soluble in alcohol and benzene and it gives violet color in potassium ferrocyanide (K4Fe(CN)6·3H2O) and sulfuric acid (H2SO4). Skatole has a double ring system which displays aromaticity that comes from the lone pair electrons on the nitrogen. It is continuous (all atoms in the ring are sp-hybridized), planar, and follows the 4n+2 rule because it has 10 pi electrons. It can be synthesized through a Fischer indole synthesis which was developed by Emil Fischer.
Skatole has been shown to cause pulmonary edema in goats, sheep, rats, and some strains of mice. It appears to selectively target Clara 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 (Miller et al., 2003).
In a 1994 report released by five top cigarette companies, skatole is one of the 599 additives to cigarettes. Its use or purpose, however, is unknown, like most cigarette additives.