A Solution to Skunk Pollution

skunksI remember the first time I ever smelled the fragrance of a skunk.  I thought someone had let off a stink bomb.  You see, even back then I was a lot more familiar with emissions from test tubes than from animals.  This certainly smelled as if someone had mixed sodium sulfide with an acid to release hydrogen sulfide-the classic smell of rotten eggs and stink bombs.  A smell potent enough to quickly drive any living creature away.  Which of course is exactly what the skunk has in mind when it lets loose from the little scent glands on either side of its rectum.

Scientists have long been intrigued by the chemical composition of skunk aroma.  Way back in 1862, the famous German chemist Friedrich Wohler received a gift of “Nordamerikanischen Stinkthiers” fluid from a “freunde in Neuyork.”  It was too smelly for the great man to work with so he gave it to one of his underlings, identified only as Dr. Swarts of Gent.

Swarts carried out the first analysis of skunk secretion and found it to be a complex mixture of many substances which distilled at different temperatures.  He was able to determine, however, that the element sulfur was prevalent in the mixture, making up some 16% of the weight.  There was a price to pay for this enlightenment.  Wohler described that his assistant’s health was adversely affected.  I’ve got to feel sorry for Swarts.  Who knows, maybe he was an ancestor!

Although chemists have been working on the problem of the exact composition of skunk fragrance for over a hundred years, only recently have the specific smelly compounds been identified.  This type of research of course is wrought with difficulty.

First of all, how does one procure a sample?  Very carefully!  Skunks are trapped and anesthetized with ether.  A blunt needle is then inserted into the anal sac of the animal and the contents removed by means of a syringe.  This sample is then subjected to analysis by an instrumental technique known as gas chromatography-mass spectrometry which can separate and identify the components of a mixture.  Literally dozens of compounds have been found in skunk extract with seven having particularly disturbing smells.  Trans-2-butene-1-thiol is the major culprit.

Now that we know this, what good is it?  Obviously, while skunk research may be academically fascinating, what we really want is a solution to the problem of the inquisitive dog or cat that has learned a lesson the hard way about the consequences of skunk chasing.  How can trans-2-butene-1-thiol and its chemical cousins be neutralized?

Tomato juice won’t do it.  That’s a myth.  The only thing tomato juice will do is create a mess, leaving us with the added problem of removing tomato juice from clothing, floors and walls.  It will also turn white dogs pink.

But despair not.  There is a solution.  Thanks to the “Indiglo” watch!  The face of this watch is treated with an electroluminescent material which glows in the dark.  An unfortunate byproduct of the manufacturing process used to make the luminescent substance is hydrogen sulfide.  Not only does this compound smell awful, it is also poisonous.

A materials engineer, Paul Krebaum, working at the plant where the electroluminescent materials were being manufactured developed a process to eliminate the smell.  He designed a system whereby the air was circulated through a solution of concentrated hydrogen peroxide and sodium hydroxide.

This idea was based on some pretty interesting chemistry.  Krebaum knew that sulfur binds quite readily to oxygen and that these “oxidized” derivatives are far less likely to smell.  Experiments showed that an alkaline solution of hydrogen peroxide readily oxidized hydrogen sulfide to odor-free sulfate.  The problem of hydrogen sulfide smell in the plant was solved!

One day, a colleague of Krebaum’s came to work with a woeful tale of an encounter between his dog and a skunk.  Krebaum had never considered the skunk problem before but he knew that the smell contained thiols.  These resembled hydrogen sulfide chemically and should also be oxidized with his reagent!

But you certainly couldn’t expose animals to 30% hydrogen peroxide.  This is dangerous stuff.  So is sodium hydroxide.  The formula had to be modified.  A little experimentation revealed that 3% peroxide would work and the sodium hydroxide could be replaced by baking soda.  Addition of a squirt of dishwashing detergent helped lift the skunk fragrance from the fur.

A magic formula was born: Take one liter of 3% hydrogen peroxide (available in pharmacies), add one quarter cup of baking soda and 1 teaspoon liquid dishwashing detergent.  Wash the cat or dog (or child) with this mixture and rinse with lots of water.  Presto!  The smell is almost completely eliminated.

This latter point is an important one.  People who have struggled with tomato juice and were successful in reducing the smell (no chemical effect, but they probably managed to physically rinse away some of the odiferous compounds) often noted that the scent would come back.

This is because the skunk mixture also contains compounds called thioacetates which are not particularly smelly but over time react with moisture to form thiols.  As the concentration of thiols increases, the skunk aroma returns.  But under the mildly alkaline conditions described in the hydrogen peroxide recipe, these thioacetates are immediately converted to thiols which in turn are oxidized.  Therefore the lingering smell is greatly reduced.

Most researchers of course are interested in eliminating the skunk stench.  But not all.  Skunk smell is known to keep bears away and to also mask the human aroma.  This is of great interest to hunters because their scent can often drive the prey away.

But of course nobody would want to carry around bottles of skunk extract, even if this were available.  The risk of an inadvertent spill would be just too great.  But a clever inventor has come up with a solution.  In fact two solutions!

“Skunk Skreen” comes in two small bottles.  One of them contains a thiol precursor which forms the stinky compound when reacted with the alkaline solution contained in the other bottle.  When desired, a few drops from each bottle are combined on a cloth producing a powerful skunk-like stench.  Bear beware!

As we know, the stench can also keep humans away.  Which is what an Alaskan inventor had in mind when he patented his “personal protector” based on skunk smell.  There is of course no time to start combining chemicals when someone is accosted so he designed a system whereby the skunk extract is enclosed in capsules which are incorporated into a credit card.  In an emergency, the card is pointed at the attacker and is bent, squirting a stream of foul scented liquid.  The card is smooth on one side and rough on the other to avoid any accidental self-spraying.

Sounds good.  Presumably the police would have little trouble tracking the culprit as the smell would linger for weeks.  That is unless the criminal knows how you have to mix hydrogen peroxide with baking soda and detergent to get the right chemistry!

Joe Schwarcz

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