Detect Hydrogen Sulfide Using Nucleophilic Aromatic Substitution

This is some very cool chemistry.  And this post is dedicated to all of those who think that the organic chemistry you learned in your class was useless.

A professor and his graduate student at the University of Oregon have developed a hydrogen sulfide detector that can detect H2S in the parts per billion range (ppb).   This detector would be very important in the study of biologically contaminated water samples.  H2S is a colorless gas that smells like rotten eggs and is world-renown for its ability to make people sick.

This is very cool chemistry and it is performed using nucleophilic aromatic substitution.  Most of you are familiar with electrophilic aromatic substitution from second semester class, so some of you may recognize nucleophilic aromatic substitution.  Here is a quick example to refresh your memory.

In this reaction, methoxide anion is displacing fluorine in order to create the new aromatic ring.  The defining characteristic of nucleophilic aromatic substitution is that you need electron withdrawing groups on your aromatic ring to make the reaction occur.  In the above example, NO2 is our electron withdrawing group.  I am not sure what they are using in their probe (spoiler alert: i have not red the article yet), but i am sure it is something similar.

The crux of the reaction, said the study’s  graduate student Leticia A. Montoya, is the reaction process in which the probe reacts with H2S to produce a distinctly identifiable purple compound. “This method allows you look selectively at hydrogen sulfide versus any other nucleophiles or biological thiols in a system,” Montoya said. “It allows you to more easily visualize where H2S is present.”

The cite for JOC is: Leticia A. Montoya, Taylor F. Pearce, Ryan J. Hansen, Lev N. Zakharov, Michael D. Pluth. Development of Selective Colorimetric Probes for Hydrogen Sulfide Based on Nucleophilic Aromatic SubstitutionThe Journal of Organic Chemistry, 2013; :

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