Is the Flask Closed or Open to Atmosphere During Reflux Heating?

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Discussion Overview

The discussion revolves around the conditions of a reflux apparatus during heating, specifically whether the flask is closed or open to the atmosphere. It addresses concerns related to solvent evaporation, pressure buildup, and the sensitivity of reactants to oxygen.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Rajini questions whether the flask in a reflux apparatus is typically closed or open to the atmosphere during heating.
  • One participant suggests that the flask is ordinarily not always closed, implying variability in practice.
  • Another participant warns against heating a completely sealed apparatus due to the risk of pressure buildup and potential explosion.
  • Rajini indicates that her reactants are oxygen sensitive and expresses a plan to pass an inert gas (argon) during heating, as she cannot use a glove box.
  • A later reply proposes the use of an oxygen scrubber with vanadium(II) chloride solution, depending on the sensitivity of the reactants.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether the flask should be closed or open during reflux heating, with multiple views presented regarding safety and the handling of sensitive reactants.

Contextual Notes

There are unresolved considerations regarding the specific conditions under which the flask should be operated, including the sensitivity of reactants and the implications of pressure buildup in a closed system.

Rajini
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Hello All,
I have a doubt in reflux apparatus. Usually when we heat some solvents in a glass flask it may evaporate..and this vapour is cooled by reflux condensor and again go into boiling solvent. So on heating the amount of solvent won't decrease or decompose. What I want to know is whether the flask is closed or left open to atmosphere while heating?
Regards, Rajini.
 
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Rajini said:
the flask is closed or left open to atmosphere while heating?
Ordinarily, NOT ALWAYS.
 
It is very seldom a good idea to heat a completely sealed apparatus, as pressure can build up and cause it to explode. If your reactants are water sensitive, a drying tube can be placed on top of the condenser to eliminate moisture, and if they are oxygen sensitive the apparatus would need to have a stream of inert gas supplied, or be run inside a glove box.
 
Hello Bystander,ManiacaLaugh,
Thanks for your reply. My reactants are oxygen sensitive. Also I cannot heat inside a glovebox/bag! So plan to pass continuously an inert gas (Ar) while heating (30 to 60 min of heating around 250 celsius is enough for my case).
Regards, Rajini.
 
Rajini said:
So plan to pass continuously an inert gas

Depending on how sensitive your reactants are, you may want to use an oxygen scrubber with vanadium(II) chloride solution.
 

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