Question

4. Handling of air-sensitive reagents a) Describe briefly or/and draw: manifold. Schlenkware, septum, bubbler, cold trap b) Describe evaporation technique using manifold c) Describe purging technique to prepare air-free solvent d) What for molecular sieves were used with some solvents? e) How to prevent air from coming into open Schenkware (for example, when adding solid reagent is needed)?

Answer 1

a) Vaccum gas manifold consists of dual manifold with a number of ports. One manifold is connected to the source and other to vaccum pump. The inert gas is vented through a bubbler while solvent vapours and gaseous products are prevented from contaminating the vaccum pump by cold trap.

Schlenkware is a reaction vessel with a side arm fitted with a ground glass stopcock. It allows the vessel to be evacuated or filled with glass.

Bubbler is glass bulb filled with a small amount of fluid. It is used to evacuate air from a reaction

Cold trap is a device that condenses vapours. It is used to prevent evacuated vapours from entering vaccum pump and contaminating it

Septum is used to cap the opening of glass wares.

c) This is the simplest method of purifying a solvent. It involves bubbling an inert gas through the solvent. The inert gas is introduced to the solvent by using a clean needle connected to the inert gas. The needle should enter the vessel with the solvent through a rubber septum and reach the bottom of the vessel. Another needle is also placed in the septum as a pressure vent and exhaust.

d) Molecular sieves are used to dry dehydration solvents. They are zeolite compounds which strongly adsorb water and have pores. Both the solvent and water adsorb to the pore surface area. But the large surface area of the pores can only be occupied by the water molecule. Thus the water molecule adsorbed can be easily removed.