We’ve seen this term a lot in the news this summer from
Palestine and Hong Kong, to even right here in the United States with Ferguson, and while it's not strictly in the field of chemistry it is chemistry in the news, and it has been incredibly prevalent in the past few years, so I thought it would be interesting to discuss the actual chemistry and science behind it. The name would imply that it is a
simple eye irritant, but in reality it can devastate a human body with
vomiting, intense pain, and even difficulty breathing. It’s considered to be a non-lethal chemical
weapon, that’s actually forbidden in warfare, but totally okay to use against
your own protesting citizens. The chemical
agent affects the mucous membranes of the eyes, nose, mouth, lungs and
sometimes the stomach. The reaction likely happens with the sulfhydryl
functional groups on enzymes which seem to affect sensory pathways, and
therefore cause the pain and irritation to those locations on the body.
There are different types of tear gas, but nowadays it
seems that CS gas is the more common form used, at least in the United
States. The chemical agent used is 2-chlorobenzalmalononitrile (seen in figure 1), which is synthesized from 2-chlorobenzaldehyde and
malononitrile using a catalyst like piperidine or pyridine (seen in figure 2). This system is supposed to be more stable and less toxic than it's predecessor CN gas, but the toxicity can fluctuate depending on how it is dispersed.
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| Figure 1 |
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| Figure 2 |
References:
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