Question

The following procedure was used to synthesize hexaphenylbenzene.

Based on the procedure, 1)what was the purpose of the silicon boiling oil ? And 2) Why was it important to wash with hexane and then ice cold toluene during the vacuum filtration?

Procedure:

1. To a 10mL round bottom flask add 100mg tetraphenylcyclopentadienone, 100mg diphenylacetylene, two boiling chips, and 1mL of high boiling silicon oil.

a. Connect water-cooled condenser to the flask and secure with clamp above a Bunser burner

b. Heat mixture over a low flame

c. Allow it to boil gently for 30 minutes

d. Put a few milliliters of toluene on ice

2. Remove from heat and cool to room temperature

a. Add 4mL of hexane to flask

3. Vacuum filter

a. Rinse with two 1mL portions of hexane.

b. Wash the product with two 2mL portions of ice cold toluene.

4. Place on watch glass to dry for 15 minutes then determine a yield and MP

Answer 1

Answer 1

The reaction in experiment is [4+2]-cycloaddition reaction between diphenylacetylene and tetraphenylcyclopentadienone followed by decarboxylation reaction. It requires high temperature for reaction thus silicone oil, a high boiling solvent (more than 250 ˚C), is used for reaction.

Answer 2

Since hexaphenylbenzene is not freely soluble in hexane and toluene. Hexane was used for removal of silicone oil from reaction. It is high boiling non polar solvent can easily removed by washing with hexane. Ice cold toluene was used for removal of unreacted reagents. Washing by hexane and ice cold toluene will give pure hexaphenylbenzene without any purification.