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Chemistry defeats the “Godzilla of odors” 

Sept. 25, 2006
Courtesy American Chemical Society
and World Science staff

In the realm of stinkers, a group of che­m­i­cals called isoni­triles may have no ri­val. Odor the­o­rist Lu­ca Tu­rin once termed iso­ni­triles “the Godzilla of smells” and the world’s worst odor. 

“The smell is in­de­scrib­a­ble. Not that it is so un­god­ly be­yond all ex­pec­t­ed lev­els of stink, which it ap­proach­es, but more it is like noth­ing you have ev­er ex­pe­ri­enced and your brain while cer­tain­ly re­pulsed to the ex­tream [sic], strug­gles to de­fine it. A dou­ble as­sault at your sen­ses. It has a per­sist­ent lin­ger on ev­ery­thing that comes near it in­clud­ing your [brain cells]. Much like a hor­ri­ble pic­ture... that can’t be purged from your mind. Even af­ter the scene changes you are left with a ghost dif­fi­cult to erad­i­cate...”

“I have no good de­scrip­tion for it. Be­sides me, the two oth­er peo­ple near­by, who were brave enough to try it... had the same thing to say, 'I can't de­s­cribe it but it sure is hor­ri­ble'. There does not seem to be a way to smell it on­ly slight­ly... I mean if you get en­ough of it to reg­is­ter, it’s en­ough to sat­u­rate your sens­es... In­i­tial ex­po­sure goes like this…You know it’s go­ing to smell so you try very hard to not get a big whiff by wav­ing the stop­per... get­ting brav­er every at­tempt un­til.. Bin­go! It’s ac­tu­al­ly fun­ny to watch some­one’s re­ac­tion when it fi­nal­ly sets in. It’s a very strange face. ...
It took an hour and a half gal­lon of IPA99%/HCL32% to clean that smell out of my hood. If you do it, plan to spend some time de-stink­ing... Ti­ny whiffs of rem­nant traces on the hood tended [to] re­mind my nose of the full scale event and I dreaded it.

— Descriptions of an isonitrile written by readers of science-madness.com, online forum for amateur chemists

“You can’t be­lieve how aw­ful they smell,” Tu­rin said. “They make you vom­it your guts out in­stant­ly.” They’ve even been patented for use as non­le­thal weapons.

The merciless stench is a key rea­son why che­m­ists have large­ly shunned the iso­ni­triles as in­gre­di­ents in im­por­t­ant chem­i­cal re­ac­tions.

But re­jec­tion of iso­ni­triles comes at a price, be­cause they have dis­tinct ad­van­tages over oth­er in­gre­di­ents for many pur­poses. 

Now, two chemists say they have come up with some­thing to salvage the dis­mal si­tua­tion: nose-friend­ly iso­ni­triles.  

Mi­chael C. Pir­rung and Su­bir Gho­rai, of the Uni­ver­si­ty of Cal­i­for­nia at Riv­er­side, are re­port­ing de­vel­op­ment of the new com­p­ounds. These so-called “isoni­trile es­ters” have pleas­ant fra­gran­ces and work just as well in  re­ac­tions as ex­ist­ing com­pounds, they claim.

The palette of aro­mas in­clude those of soy, malt, nat­u­ral rub­ber, mild cher­ry and even taf­fy, ac­cord­ing to a study in the Sept. 20 is­sue of the Jour­nal of the Amer­i­can Chem­i­cal So­ci­e­ty.

Another prob­lem with usual iso­ni­triles is that ex­ist­ing recipes for mak­ing them re­quire use of haz­ard­ous com­pounds. Pir­rung and Gho­rai say theirs can be made safe­ly.

Al­so known as or­gan­ic iso­cyanides, isoni­triles are de­fined as com­pounds with a ni­tro­gen and a car­bon at­om con­nec­ted by a link known as a tri­ple co­va­lent bond.

Witnesses to the stench claim words cannot describe it. But af­ter read­ing ma­ny first-hand ac­counts of their or­deals, one be­gins to piece to­ge­ther a dim pic­ture of the od­or as a sort of beast that takes the whole sen­s­ory ap­pa­ra­tus hos­tage, leav­ing vic­tims feel­ing ab­used and vio­la­ted. Like a bru­tal ty­rant, it seems, the smell makes itself felt even after one leaves its im­me­di­ate pre­sence (see sidebar).  


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In the realm of real stinkers, a group of chemical compounds called isonitriles may have no rival. Renowned odor theorist Luca Turin once termed the isonitriles “the Godzilla of smells” and the world’s worst odor. “You can’t believe how awful they smell,” Turin said. “They make you vomit your guts out instantly.” They’ve even been patented for use as nonlethal weapons. The atrocious stench is a key reason why chemists have largely shunned the isonitriles as ingredients in important chemical reactions, even though the isonitriles have distinct advantages over other ingredients. In addition, existing recipes for making isonitriles require use of hazardous compounds. Michael C. Pirrung and Subir Ghorai, of the University of California at Riverside, now are reporting development of a new family of isonitriles. Their isonitrile esters can be made safely, work just as well in chemical synthesis reactions as existing compounds and have a pleasant odor. The odors include that of soy, malt, natural rubber, mild cherry and even taffy, according to a study scheduled for publication in the Sept. 20 issue of the Journal of the American Chemical Society. Also known as organic isocyanides, isonitriles are defined as compounds with a nitrogen and a carbon atom tied together by a link called a triple covalent bond.