organosurf
Harmless
Posts: 8
Registered: 11-12-2012
Member Is Offline
Mood: No Mood
|
|
Dean Stark v/s Packed Reflux column
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.
|
|
|
Tsjerk
International Hazard
Posts: 3022
Registered: 20-4-2005
Location: Netherlands
Member Is Offline
Mood: Mood
|
|
I think that should work when the temperature of the reaction is high enough to make enough water evaporate, or when your solvent forms an azeotrope
with your water.
But if I remember correctly, the absorption of water by molecular sieves isn't particularly quick.
The water weighing won't work though, as water also evaporates from sieves upon heating.
[Edited on 10-3-2014 by Tsjerk]
|
|
|
organosurf
Harmless
Posts: 8
Registered: 11-12-2012
Member Is Offline
Mood: No Mood
|
|
Thanks, I got the points which I missed eg the rate of water adsorption by sieves and final weighing errors.
|
|
|
Oscilllator
National Hazard
Posts: 659
Registered: 8-10-2012
Location: The aqueous layer
Member Is Offline
Mood: No Mood
|
|
Look at the most recent page of the pretty pictures thread - I posted there an improvised dean-stark apparatus, and its definitely worth looking into.
|
|
|
Paddywhacker
Hazard to Others
Posts: 478
Registered: 28-2-2009
Member Is Offline
Mood: No Mood
|
|
Yes, this is a technique sometimes used, especially with the molecular sieve being held in a soxhlet apparatus. Be aware though that molecular sieve
is alkaline enough to catalyse the aldol condensation, so ketones like acetone might not be good choices of solvent.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
