Field of Science

Perils of Summer 2: Mephitis Squared

It's war on my dad's farm: humans versus Mephitis mephitis, night time maneuvers complete with chemical weapons. Currently the skunks hold the high ground.

Last night my brother's dog threatened a skunk, with predictable results. The collateral damage included my shoes and feet. The Reverend's Wife produced a bottle of something guaranteed to elminate the smell and we decontaminated me and the dog on the lawn. I was more cooperative about being hosed down. The odor was overpowering, and even after twice deskunking me, my kids swore I still smelled of skunk.

Skunk musk is a mixture of low molecular weight thiols, sulfur containing compounds that have the basic structure ☐-S-H (where the box represents a functional group, such as methyl or butyl), and related compounds called thioacetates. Most thiols have a characteristic, and awful, odor. (Thioacetates don't smell quite so badly.) The simplest thiol is methane thiol, also known as methyl mercaptan, which is used to spike methane (natural gas) so that leaks can be detected. (Methane is actually odorless.) Humans can detect thiols at very low concentrations, less than 1 ppm, which explains why my kids could still pick up the odor.

Skunk odor can be neutralized by converting the thiols to less odiferous molecules. One way this can be accomplished is by reacting the thiols with hydrogen peroxide, which oxidizes the thiol to a sulfonic acid ( ☐-SO3H), which has virtually no odor. Bleach (a strong oxidizing agent) will work as well. A similar technology is used to remove thiols from industrial waste water, where the thiols are converted to disulfides ( ☐-S-S- ☐), which are oils that separate easily from the water.



Mercaptan comes from the Latin mercurium captans, something that seizes or captures mercury. Sulfur reacts very effectively with mercury, and one way to clean up a mercury spill is to sprinkle sulfur on the mercury. Thiol is Greek for sulfur.

If you need a recipe to remove skunk odor, try Humbolt's list. I can personally vouch for the effectiveness of the pet/human version. Note that tomato juice is not particularly effective.

1-para-methen-8-thiol is an uncharacteristically and pleasantly scented thiol more commonly known as grapefruit mercaptan.

More demystified chemical perils of summer...

3 comments:

  1. Grapefruit seems very "special" at the molecular level - uniquely pleasantly scented thiols, and the special drug interaction properties of furanocoumarins. Is there something special going on, biochemically, with grapefruit? I mean, something in its genes that makes it more different than, say, a lemon is from an orange.

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