Chemistry of Skunk SprayWilliam F. Wood, Department of Chemistry Humboldt State University, Arcata, CA 95521 E-Mail firstname.lastname@example.org Phone (707) 826-3109
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Striped Skunk (Mephitis mephitis)
Skunk defensive secretion is composed of seven major volatile components. These can be divided into two major groups of compounds, thiols and acetate derivatives of these thiols. Two of the thiols are responsible for the strongly repellent odor of the secretion, (E )-2-butene-1-thiol and 3-methyl-1-butanethiol. The third thiol, 2-quinolinemethanethiol, is not as odoriferous due to its low volatility and the fact that large thiols do not trigger the human olfactory receptor. The chemical structure of these compounds and their percent (four individuals) in the defensive secretion are shown in the following illustration.
A second major class of compound in skunk spray are thioacetate derivatives of the three thiols. These compounds are not as odoriferous as the thiols, but are easily converted to the more potent thiols on water hydrolysis. This chemical conversion may be why pets who have previously been sprayed by skunks will again have a faint "skunky" odor on damp evenings. Thioacetate derivatives of (E )-2-butene-1-thiol and 3-methyl-1-butanethiol trapped in the animal's hair could be releasing the smelly thiols under the damp conditions. The chemical structure of these thioacetates and their percent in the defensive secretion are shown in the following illustration.
A third type of compound is found in this secretion, it is the alkaloid 2-methylquinoline. This compound is clearly related to 2-quinolinemethanethiol and S-2-quinolinemethyl thioacetate. Perhaps 2-methylquinoline is a product in the biosynthesis of these two compounds. The structure and percent of 2-methylquinoline in skunk secretion follows.
Deodorizing Skunk Spray
To get rid of the odor of skunk spray, it is necessary to change the thiols into compounds that have little or no odor. This can easily be done by oxidizing the thiols to sulfonic acids. Many oxidizing agents can effect this change. Hydrogen peroxide and baking soda (sodium bicarbonate) are mild enough to be used on pets although it may change their hair color. For inanimate objects sodium hypochlorite solutions (liquid laundry bleach) are cheap and effective. The chemical reaction for this transformation follows. (Recipes for deodorizing spray.)
References: "New Components in Defensive Secretion of the Striped Skunk, Mephitis mephitis." William F. Wood, J. Chemical Ecology 16, 2057-2065 (1990). "Some chemical constituents of the scent of the striped skunk (Mephitis mephitis)." Andersen, K. K., and Bernstein, D. T. J. Chemical Ecology 1, 493-499 (1975).
Spotted Skunk (Spilogale gracilis*)
The defensive secretion of the spotted skunk differs from that of the striped skunk in that it only contains thiols and the thioacetates are not present. The two major thiols of the striped skunk, (E )-2-butene-1-thiol and 3-methyl-1-butanethiol are also the major components in the secretion of the spotted skunk. A third thiol, 2-phenylethanethiol, was present at moderate concentration in this smaller skunk. The chemical structure of these compounds and their percent (two individuals) in the defensive secretion are shown in the following illustration.
A number of minor components (less than 1%) were also identified from the spotted skunk. The chemical structure of these compounds and their percent (two individuals) in the defensive secretion are shown in the following illustration.
* Spilogale putorius has recently been divided into two species, S. putorius in the Eastern part of the United States and S. gracilis in the West.
Reference: "Volatile Components In Defensive Spray of the Spotted
Skunk, Spilogale putorius," William F. Wood, Christopher G.
Morgan and Alison Miller, J. Chemical Ecology 17, 1415-1420 (1991).
Hog-nosed Skunk (Conepatus mesoleucus*)
The defensive secretion of the hog-nosed skunk differs from that of the spotted skunk and the striped skunk. Like the striped skunk, it does contain thioacetate derivatives of the thiols in the secretion. Also, a major component of the striped and spotted skunks' secretion is missing from the secretion of this species. The major components from this skunk's secretion are (E )-2-butene-1-thiol and S-(E )-2-butenyl thioacetate. The chemical structure of these compounds and their percent (one individuals) in the defensive secretion are shown in the following illustration.
The minor components in this secretion are phenylmethanethiol, 2-methylquinoline, 2-quinolinemethanethiol and bis[(E )-2-butenyl] disulfide. The chemical structure of these compounds and their percent (one individuals) in the defensive secretion are shown in the following illustration.
*Recent research indicates the two species of hog-nosed skunks, Conepatus mesoleucas and C. leuconotus may be the same species. Thus, according to the rules of zoological nomenclature, the one that was described first has priority. If they are the same species, the nameC. leuconotus will be used. (Pers. Communication Dr. Jerry Dragoo, University of New Mexico, email@example.com)
Reference: "Volatile Components in Defensive Spray of the Hog-nosed Skunk, Conepatus mesoleucus" William F. Wood, Christoph O. Fisher and Gary A. Graham, J. Chemical Ecology 19, 837-841 (1993).
© William F. Wood, 1998. Updated on 6 October 1998.