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Topic: Dean Stark v/s Packed Reflux column  (Read 3237 times)

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Offline organosurf

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Dean Stark v/s Packed Reflux column
« on: March 10, 2014, 05:19:33 AM »
Dean Stark apparatus is used to remove water formed in a reaction. This apparatus is complex in design and is also of two types.
Can Molecular Sieves ( 3A or 4A ) be employed either in the flask, a procedure that may be limited due to acidic or basic nature of reactants OR more so, in the Reflux column as a packed “cartridge” that can be inserted and removed as the reaction progresses.
In a packed column as the reactants come in contact with the molecular sieves, they condense and drip back into the flask, adsorbing only water in the process.
The cartridge can be a small diameter wire gauze tube filled with granules of the molecular sieve.
To know the amount of water adsorbed, the cartridge can be warmed in an oven to expel volatile organics and weighed ( before and after  insertion ).
Especially suited for reactants whose boiling point is less than water.


Offline AlphaScent

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Re: Dean Stark v/s Packed Reflux column
« Reply #1 on: March 10, 2014, 12:32:49 PM »
The apparatus is not complex.  It is one piece, the trap.  Then a condenser is attached above it.  As long as water is not free to react in the reaction and the equilibrium is shifted to products, it does not matter.  I have no comment on sieves since I have never done that.  What solvent are you trying to use.  Water usually needs to form an azeotrope.
If you're not part of the solution, then you're part of the precipitate

Offline zsinger

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Re: Dean Stark v/s Packed Reflux column
« Reply #2 on: March 10, 2014, 04:30:32 PM »
DS is always way easier and less expensive.
           -Z
"The answer is of zero significance if one cannot distinctly arrive at said place with an explanation"

Offline clarkstill

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Re: Dean Stark v/s Packed Reflux column
« Reply #3 on: March 13, 2014, 03:22:19 PM »
Also, sieves are available either balled or as a powder; there's no need for the cartridge apparatus you describe, just filter them off at the end of the reaction. Or use MgSO4 instead, it's a good dessicant and a Lewis acid so good for e.g. imine formations (sieves are generally a bit basic).

Offline organosurf

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Re: Dean Stark v/s Packed Reflux column
« Reply #4 on: March 14, 2014, 12:47:41 PM »
Thanks all, the solvent is water miscible, n-butanol. As both water and butanol rise in the reflux column, it was envisaged that the water would be adsorbed by the eg 3A molecular sieve ( granules ) leaving the n-butanol to trickle back into the reaction flask. Other desiccants like MgSO4 can adversely affect the outcome due to probable ion participation.
Molecular sieves have a water adsorption capacity of approx 20% w/w, retain water upto 200 deg c fluid temps, unreactive neutral conditions, 3A does not adsorb large molecules like n-butanol, can be recycled.


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