How to use Molecular sieves to dry an organic solvent?

Question

How to use Molecular sieves to dry an organic solvent? Also, how to recover the Molecular sieves after use? Thanks for help. Appreciate if can provide related reference.

Answer 1

Molecular sieves are a type of zeolite. Zeolites are porous minerals; these pores are very small, on the order of angstroms.
In organic chemistry, 4A (angstrom) molecular sieves are often used. They must first be dried in an oven to remove water obtained from storage. Some people insist on using a vacuum oven--I cannot say for sure if this is necessary. After cooling in a dessicator, they are ready to use.
I have used mol. sieves mostly as a way to remove water during reactions in which water is produced but is harmful to the product, or to drive the reaction forward (Le Chatalier's principle - removing a product drives reaction forward). However, you can also distill solvents using molecular sieves. Simply place them in the round-bottom flask with the solvent. The sieves will trap the water, so the distillate will not have any water in it.

I think you can reuse them by redrying them. Let the organic solvent evaporate, then place in the oven.

As a note of caution, molecular sieves give off "dust" slowly, so I wouldn't reuse them indefinitely, as they turn the solvent cloudy.

If you aren't sure about this, there are chemical methods of drying organic solvents. Armarego's Purification of Organic Compounds contains appropriate reagents for different solvents.

Answer 2

Probably excessive information but I enjoyed the article enough to think it's worth sharing. As removal of moisture/adsorbtion is a function of time and amount of molecular sieves(sites for adsorbtion), this seems important. Without performing a titration and using fresh molecular seives(or regenerated but not too old as they do have a life-time) this will give a range for about how dry the solvent may be.

Answer 3

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Molecular sieves are a type of porous mineral. The pores are very small (on the order of angstroms), which means that only small atoms or molecules can enter into the solid molecular sieve. In organic chemistry, the most common use of molecular sieves is removal of water. Water gets trapped inside 4 and 3 angstrom size molecular sieves. In reactions where water is a product, using molecular sieves drives the reaction forward (removal of a product shifts the equilibrium to the right). Molecular sieves are also used to distill organic solvent. If you do not add molecular sieves, or something else that removes water, the distillate will contain a small amount of water, which is sometimes too much water for very sensitive reactions, such as Grignard reactions. In order for them to work, they must be extensively dried before use.

Answer 4

The first answer is spot on. just tip it in the bottle and leave for as long as possible. molecular sieve is usually dusty so filter the solvent before use if this is critical to your process. oven drying regenerates the sieve but be very careful to let any flammable solvent evaporate off in a safe place before the sieve is dried in this way

Answer 5

How To Use Molecular Sieves

Answer 6

In most cases you can dry solvents by putting molecular sieve in the bottle. You should be able to recover it after use by drying it in an oven.

Answer 7

Hope this helps!