I recently felt the need to apply oxygen free conditions to a reaction that I had done previously under air so that I could determine whether O2 took part in its mechanism. This required doing the reaction under nitrogen, but also the removal of dissolved O2 from the solvent. O2 can be displaced from solvents by bubbling nitrogen gas through for 30 min. I was using DMF and I found precedence for O2 removal in a 1972 Organic Syntheses entry where an oxygen sensitive chromium reagent was employed. Note that many techniques to remove O2 ignore or even introduce water to the solvent and or nitrogen.
I learned that our building nitrogen at RMIT is obtained by vapour run off from a tank of liquid nitrogen at the bottom of the building. I wished to test this nitrogen and to be confident that it was free of any oxygen so that I knew if my reaction had was occurring in the presence of O2. A way to do this is described in 'The Chemist's Companion: A Handbook of Practical Data, Techniques, and References' by Gordon and Ford, Wiley publishing, 1972. Here it is described to use pyrogallol in strong alkaline solution which will absorb any O2 and turn red in the process.
 The recipe calls for 5 g of pyrogallol (1,2,3-trihydroxybenzene) into a solution of 100 mL of water with 120 g of KOH. Pyrogallol comes as a white shard-like crystal power. The instructions given in the old chemists manuals say that this will be a colourless solution that will turn red/brown as it chemically absorbs O2. | 
Pyrogallol crystals
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Simply preparing the above described solution on the bench with no effort to exclude air resulted in a dark red solution that becomes closer to brown solution. See image below.
Oxidized solution of pyrogallol in KOH/water.
I found that the only way to prepare the pyrogallol solution mostly free of colour was to place the 5 g of pyrogallol into the empty Dreschel and vacuum out the air and fill with nitrogen. I then prepared the 120 g of KOH into 100 mL of water solution in a beaker and bubbled N2 gas through it using a rubber tube/Pasteur pipette for 30 min. With the Dreshcel under slight positive pressure of N2, I opened it and quickly poured the contents of the beaker through. I sealed the bottle and found that I had made a solution that was almost colourless. It was clear enough to see through.
The pyrogallol solution immediately after it has been prepared. N2 is bubbling through.
Note that while passing nitrogen through such a solution removes O2 but adds some H2O.
Trying to get a colourless version of the solution into a Dreschel bottle outside of a glovebox is impracticable. I was able to prepare one with only a slight redness to it but that was still clear enough to see through. This nicely verified the quality of my building's nitrogen as the colour did not get any redder, even after 18h of bubbling
Trying to get a colourless version of the solution into a Dreschel bottle outside of a glovebox is impracticable. I was able to prepare one with only a slight redness to it but that was still clear enough to see through. This nicely verified the quality of my building's nitrogen as the colour did not get any redder, even after 18h of bubbling
The setup after 18 h. Note that the pyrogallol solution in the Dreschel bottle is still the same shade of red.
This setup is of course lacking a Schlenk line and is to be avoided for future experiments.
After I finished the reaction and opened the Dreschel to clean up, it's contents became dark red upon just a few seconds exposure to air.
After I finished the reaction and opened the Dreschel to clean up, it's contents became dark red upon just a few seconds exposure to air.
