Monday, April 29, 2013

Sometimes the Best Reactions are Those that don't Run

As chemists we pride ourselves on our abilities to get reactions to run. Reactions that don't run are failures - or are they?

I have spent considerable time working on preventing reactions from occurring in plastics. Oxidation is very seldom desirable, and so I'll add antioxidants to prevent an oxidation reaction. The same is true for ozonation (which is different than oxidation), in which case I'll antiozonants, and UV degradation, in which case I'll add a UV absorbers (plus hindered amines plus...). And while I can seldom prevent a plastic from burning, adding flame retardants can slow the fire or extinguish it once an external flame source is removed. In the same vein, there are numerous additives that can be used to prevent microbial/fungal attack to a polymer as well (although this is bordering on biochemistry!).

A more extreme example of preventing a reaction is seen in 2-part polymers, such as silicones, urethanes, which physical separation is used to prevent a reaction from occurring. And then there are the "1-part" silicones, urethanes, acrylates... that are actually 2-parts systems. I'm talking about the materials where the other part is atmospheric moisture. The packaging is design to prevent moisture diffusion into the base polymer.

Last week during #RealTimeChem week on Twitter, many people were all excited about the success they had in getting their reactions to run. But I can often come home just as excited about reactions that I have prevented from running.

1 comment:

Andrew Bissette said...

Interesting perspective! Even in "normal" synthesis, getting a reaction to work well is often as much a case of getting the wrong reactions to stop.

Pretty much every chemist does this daily through the routine exclusion of water, but also any selectivity by definition involves promoting the right reaction and/or shutting down the wrong reactions. Perhaps most elegantly realised in asymmetric catalysis - selectively killing one enantiomer of the same reaction.