Saturday, 12 December 2015
How to dry molecular sieves?
In this post, I will move from the topic of asymmetric catalysis and I will explain a basic operation in organic chemistry lab.
Laboratories involved with organic synthesis require efficient methods with which to dry (i.e. removal of water) organic solvents. In some cases, water present in organic solvents can be deleterious for the chemical reaction since reactants and/or reagents can react faster with water being deactivated with the consequent loss of performance of the reaction.
Among the different methods available for drying solvents, the use of molecular sieves is one of the most efficient ones. A molecular sieve is a material with pores (very small holes) of uniform size. These pore diameters are of the dimensions of small molecules, thus large molecules cannot be absorbed, while smaller molecules can.
From the chemistry point of view, molecular sieves are crystalline metal aluminosilicates having a three dimensional interconnecting network of silica and alumina tetrahedra. Natural water of hydration is removed from this network by heating to produce uniform cavities which selectively adsorb molecules of a specific size.
Commercially available molecular sieves contain water, therefore it is needed to remove this water content before use as dessicant in organic solvents. This process is called "activation" of molecular sieves.
In the following video created by my lab mate Rasmus Mose you will find a short description on how to activate molecular sieves and store solvents in a schlenk flask.
Very useful in case you work in an organic chemistry lab!