From Why is the decarboxylation of 2-hydroxybenzoic acid (and related compounds) done 'under nitrogen'? I confirmed that nitrogen is used to exclude oxygen - in order to prevent oxidation of the material.

Can $\ce{CO_2}$ be substituted for nitrogen, or will the presence of carbon dioxide slow down the decarboxylation reaction (which is causing carbon dioxide to be released)?

  • $\begingroup$ Carbon dioxide is relatively reactive in comparison to nitrogen and argon. You cannot assume your $\ce{CO2}$ blanket won't interfere with your reaction. $\endgroup$ – Jori Mar 22 '15 at 11:50
  • $\begingroup$ @Jori "You cannot assume your CO2 blanket won't interfere with your reaction." ..hmm. Not good. But are you saying that you know it will interfere with decarboxylation reaction, or more that it is (simply) rash to presume it will be OK? BTW - how did you make that 2 as a subscript in a comment? I use <sub>..</sub> for the question. $\endgroup$ – Andrew Thompson Mar 22 '15 at 11:57

Because nitrogen is the standard inert gas in lab practice. If you are "rich" You can use argon, but carbon dioxide is seldom used, because it won't work on alkaline solutions.

or will the presence of carbon dioxide slow down the reaction

First, what you presumably mean is influencing the equilibrium unfavourably, don't you? You should learn to discern kinetics and equilibrium.

Answer: not really. Whether you have a carbon dioxide atmosphere or not will shift the decomposition temperature not more than some degrees.

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    $\begingroup$ Excellent. I wanted to try CO2 since it is a lot easier (& cheaper) to thaw some dry ice and use the resulting gas than it is to get a compressed bottle of nitrogen (or argon) and a regulator. And no, I'm not rich.. For nitrogen it would be 140 dollars for the regulator, and around 85 for 1 cubic meter of scientific grade nitrogen. Now I just have to decide between heating the material to be decarboxylated using a liquid bath, or heating the CO2 before it goes into the reaction chamber.. $\endgroup$ – Andrew Thompson Mar 22 '15 at 10:50

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