Skatole

Key takeaways

Skatole belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Skatole to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Skatole from memory before moving on to harder problems.

Reference excerpt

Skatole (also spelled skatol) or 3-methylindole is an organic compound belonging to the indole family. It occurs naturally in the feces of mammals and birds and is the primary contributor to fecal odor. At high to moderate concentrations, its aroma is described as "animal, fecal, naphthyl, civet". 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 has also been identified in certain cannabis varieties. Skatole is one of the volatile compounds in human breath associated with halitosis. It is used as a fragrance and fixative in many perfumes and as an aroma compound. It is also used in low concentrations in some ice cream as a flavor enhancer. Its name derives from the Greek root skato-, meaning feces. Skatole was discovered in 1877 by the German physician Ludwig Brieger (1849–1919).

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. [I was occupied initially with the investigation of the volatile components of excrement in acidic solution. One obtained thereby volatile fatty acids: acetic acid; normal and isobutyric acid; as well as the aromatic substances: phenol, indole and a new indole-derived substance which I will name "skatole".]

Biosynthesis, chemical synthesis, and reactions Skatole is derived from the amino acid tryptophan in the digestive tract of mammals. Tryptophan is converted to indoleacetic acid, which decarboxylates to give the methylindole. Once it is created in the digestive tract of mammals, it is metabolized by cytochrome P450 enzymes in the liver. Skatole can be prepared in the laboratory via the Fischer indole synthesis, a method for the formation of indole derivatives from phenylhydrazines and carbonyl compounds. Phenylhydrazine and propanal can be used. A simplified reaction scheme is shown below.

It gives a violet color upon treatment with potassium ferrocyanide.

Insect studies

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 for these bees for study. It is also known for being an 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. CSO sites are thus of particular interest when studying mosquito-borne diseases such as West Nile virus. The release of skatole by certain parasitic wasps in the family Bethylidae is used to determine which subfamily the species belongs to. Species of the Epyrinae subfamily release skatole, while those in the Bethylinae subfamily release a different chemical, spiroacetal.

Animal studies Skatole occurs naturally in the feces of all species of mammals and birds, and in the bovine rumen. 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). With the testicular steroid androstenone, skatole is regarded as a principal determinant of boar taint. High amounts of skatole stored in the fat tissue of pigs corresponds with boar taint. To address this, vaccinations with an immunogenic amount of Lawsonia intracellularis antigen are being studied. This antigen reduces the uptake of skatole into the fat of pigs, thus reducing the effect of boar taint. Another method used to address skatole concentration in fat tissue is supplementing the pig's diet with 3% chestnut wood extract. This method showed that intestinal skatole concentration decreased by more than 50%.

Applications Skatole is the starting material used in the synthesis of:

Atiprosin Nerispirdine (besipirdine analog). 3-Methyl-3-piperidinooxindole [55490-24-9] (see page 751):

See also 1-Methylindole 2-Methylindole (methylketol) 5-Methylindole 7-Methylindole Cadaverine

References

Illustrations

Worked examples

Example 1 — a first encounter with Skatole

Start with the simplest possible case. Write down what Skatole claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Skatole before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Skatole ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Skatole

In research: Skatole appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Skatole in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Skatole is common in secondary-school and first-year university syllabi. It links to neighbouring topics Feces, Foul-smelling chemicals, Methylindoles, so understanding it makes those chapters shorter.
In everyday life: Look for Skatole outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Skatole in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Skatole means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Skatole out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Skatole in simple terms?

Skatole (also spelled skatol) or 3-methylindole is an organic compound belonging to the indole family. It occurs naturally in the feces of mammals and birds and is the primary contributor to fecal odor.

Why does Skatole matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Skatole?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Skatole.