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In the procedure for the synthesis of N-anisoyl-2-pyrrolidinone that was given to me, it is written that when triethylamine is added, a "fog" is observed inside the flask.

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Triethylamine is added to neutralize the hydrochloric acid that is generated during the reaction, forming triethylammonium chloride.

I searched for similar procedures involving an acyl chloride and an amine, but the formation of a "fog" is never mentioned. A quick search on the internet gave me no clue. In my experience I have never witnessed the formation of a "fog" with this kind of reactions.

Since I cannot enter the lab due to the COVID-19 restrictions, I cannot perform the reaction now, can someone help me to understand if and possibly why in this case a "fog" is formed?

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    $\begingroup$ What happens if you put two small beakers with conc. HCl and conc. NH3 next to each other? $\endgroup$ – Karl Sep 3 '20 at 17:46
  • $\begingroup$ @Karl I edited the post, I apologize for my mistake. $\endgroup$ – Violet Sep 3 '20 at 17:51
  • $\begingroup$ I'm not sure what you wrote is actually wrong, just the alternative is more usual here, and should imo ring a bell. :-) $\endgroup$ – Karl Sep 3 '20 at 17:56
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You are adding Et3N to a solution that contains HCl as a reaction product. That means there will be HCl vapour above the solution. The Et3N is fairly volatile so there will be Et3N vapour around the addition stream/droplets and this will react with the HCl vapour as it is added to give triethylammonium chloride. This gives you the fog.

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