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Monday, April 20, 2015

Chemical Weapons

Actresses perform with an orange curtain at a ceremony to mark Agent Orange Day in Hanoi. U.S. warplanes dropped about 18 million gallons of the defoliant on southern Vietnam during the 1960s. (Kham/Reuters)
We're coming up on the 100th anniversary of the first use of chlorine gas in WW1. That will be Wednesday. Sarah Everts has a good story about the use of poison gas during WW1 on the Chemical Engineering website.
    At the end of the story there is a little multiple choice quiz. This should be a snap, all these web quizzes are like Trivial Pursuit. Whatever pops into your head in response is probably the right answer. Not here. I got 4 out of 8, and that was only because I was lucky.
    Reviewing the correct answers, I noticed that the names of two chemicals that go into making Agent Orange (the Vietnam War era herbicide) are very similar:
  • 2,4,5-Trichlorophenoxyacetic acid and 
  • 2,4  - dichlorophenoxyacetic acid
They are almost identical. One has a 2,5-Tri prefix, the other a 2,4-di prefix. The rest of it can be broken down as follows:
  • chloro - contains chlorine, same stuff in you find in bleach and swimming pools.
  • pheno - phenol is a basic building block for many plastics, amongst other things.
  • oxy - short for oxygen
  • acetic acid - vinegar, yuck.
The problems with Agent Orange came from the process used to make the first chemical. Producing chemical #1 entails some heating. If you let it get too hot, some of the substance will turn into
  • 2,3,7,8-tetrachlorodibenzo-para-dioxin
or TCDD for shot. The only thing this chemical name has in common with the first two is the chloro part.
TCDD has been described by Yale biologist Arthur Galston as "perhaps the most toxic molecule ever synthesized by man".

A note about the picture: I don't recommend Googling for Agent Orange images. Most of what you will get back is real horror show.

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