[organosurf]

Dear All,

Can a Dean-Stark trap / apparatus be used in a reaction where water is eliminated but the reactants and solvents have low boiling points and are soluble in water ?
Eg. Methanol / Acetone / Water mix under reflux at 80 °C ?
Wouldn’t the volatile solvents evaporate off first and rather quickly ?
Even if water was collected in the trap, wouldn’t it also contain the soluble methanol and acetone,( both do not form azeotropes with water ) thus making it difficult to distinguish or estimate how much water is actually eliminated ?
In such a case, will the use of a Dean-Stark trap be justified / useful / serve its intended purpose ?
Can the use of molecular sieves effectively circumvent this at reflux temperatures of upto 80 °C ?
Thanks

[discodermolide]

The whole point of a Dean-Stark is to azeotrope the water off with an inmiscible solvent, for example toluene/water.

[Wastrel]

You can have mixtures that are miscible to some extent, for example benzene, water ethanol, but you need to form a heterogeneous azeotrope, that is to say an azeotrope that splits when it condenses.  The Dean-Stark trap is just a trap in the condensate to retain one layer.  The most water is usually in the denser one.

If you wanted to filter the condensate through molecular sieves instead that might work but they don't work well at elevated temperatures.

[organosurf]

Hi,
The problem is having a lower boiling point solvents ( methanol & acetone ) together with benzene.
I do agree with the necessity in formation of an azeotrope to eliminate the water ( Benzene + water )
The methanol & acetone will distill faster from the reaction mix and also condense faster in the water layer, forming a homogenous mix with water and thus difficulty in knowing how much methanol / acetone to add so as to make up for the loss when water is drained.
The water trap has a lowest temperature.
Can molecular sieves be added DIRECTLY to the water trap ?
                       Alternatively,
Can anhydrous CuCl2 / CuSO4 be added to the water trap ? ( This way, the water binds to the CuSO4 to give the pentahydrate, which also serves as a visual indicator ? ) Main drawback is the hydrated CuCl2 / CuSO4 shouldn't find it's way into the reaction flask
The methanol & acetone can flow back to the reaction flask 

[discodermolide]

I seem to remember that mol. sieves will also absorb methanol.
The idea with anhydrous copper sulphate is not bad, but add it directly to the reaction flask, no need for a Dean-Stark.
You can also do this with anhydrous Magnesium or sodium sulphate.

[organosurf]

Thanks !