Hexaphenylbenzene has been prepared by heating tetraphenylcyclopentadienone and diphenylacetylene without solvent and by trimerization of diphenylacetylene with bis-(benzonitrile)-palladium chloride and other catalysts. The reaction proceeds via a Diels-Alder reaction to give the hexaphenyldienone, which then eliminates carbon monoxide.
Multi-Step Synthesis of hexaphenylbenzene from benzil
Procedure: Add 0.8 g of tetraphenylcyclopentadienone, 0.8 g of diphenylacetylene (synthesized by you in CH 2270 lab last semester), and 4 g of benzophenone to a 25 mL round-bottom flask. Place a magnetic stir bar in the flask. Make sure no material lodges on the neck or walls of the flask. Attach the condenser to the round-bottom flask. Do not attach the hoses. The condenser will be used as an “air condenser” for this experiment. Heat the reaction mixture VERY HIGH with the sand bath on the hot plate/stirrer. Benzophenone is your solvent and its boiling point is over 300 °C! Heat the reaction mixture to reflux. Carbon monoxide is evolved, the purple color begins to fade in 15-20 minutes, and the color changes to a reddish brown in 25-30 minutes. When no further lightening in color is observed (after about 45 minutes), the heat is removed and 1 mL of diphenyl ether is added to prevent subsequent solidification of the benzophenone. The crystals that separate are brought into solution by reheating and the solution is let stand for crystallization at room temperature. The product is collected and washed free of brown solvent with toluene to give colorless plates.
