How Nonreactive can a Material Really Be?

By Tristan Maxson

As a scientist, we are commonly taught that some materials are chemically inactive for reactions; this is not true. These inert, or nonreactive, materials include things such as glassware, plastics, nitrogen, and the noble gases. Due to this being taught to us very early in our education, it is hard to think of these materials as being harmful for some types of chemistry due to the rarity of reactions occurring with these.

Glassware is a more well-known example of an inert material being chemically active since it can be etched away by some corrosive chemicals such as hydrofluoric acid and piranha acid, both of which are dangerous to work with. The problem with this type of understanding is that it does not present itself with more minor problems that can occur without the glass visibly changing. Glass can be affected by acids and bases without being destroyed when the oxygen atoms on the surface of the glass are acidified or neutralized, potentially affecting the reaction or measurements being done in them.

Plastics are sometimes known to be inert, but many of them are not inert to common lab chemicals. ABS plastics are dissolved by acetone, PLA plastics are degraded by water and sunlight, and some plastics such as Nylon are not compatible with acids. These plastics would not be used by a lab in direct contact with a reaction, but Teflon is incredibly common to find as a coating on stir bars. Recently a group has published their findings on how stir bars in their labs showed catalytic activity for organic reactions, creating unpredictable results due to a material that is universally considered to be inert in presence of almost all reactants. We have incorporated their findings into my own research where we have started using glass stir bars for one project. By switching stir bars and making a few other changes, we were able to reduce the error in our experiments from about 10% to closer to 1-2%.

Oxygen is well understood as a chemically active gas which can be crucial for life, combustion of materials, and for corrosion of metals. To remove oxygen from reactions, it is common to purge the solution with nitrogen or noble gases such as argon to displace the oxygen. While these gases are normally inert, it is well known that some noble gases can form molecules with fluorine such as xenon hexafluoride, but this would be unlikely to happen unintentionally. Nitrogen is also very inert but under high pressure or temperature conditions it can become reactive and some groups have been working to find ways to make it reactive at ambient conditions. Typically its strong bond is hard to break, but that doesn’t make it impossible to break when in contact with a catalyst lowering the barrier for dissociation.