Friedel-Crafts Acylation

Introduction:

The aim of this prac is to build the ability to design an experimental procedure of the Friedel-craft acylation of an unknown compound. Friedel- craft acylation involves two main types: alkylation and acylation reactions. Both process are done through the substitution of electrophilic aromatic. Alkylation of an aromatic ring with an alkyl halide with a strong Lewis acid is required. The amount calculated to be used in the reaction is based on the 5 millimolar and ratio for each of the reagent are acetyl chloride (1.1): Aluminium chloride (1.1) : unknown B (1).

Experimental method:

Weigh out 0.73g of Aluminium chloride and transfer to a 100ml round bottom flask using the weighing paper as a funnel. Carefully add 2ml of DCM (dichloromethane) and 1ml of Acetyl chloride in DCM to the round bottom flask. Add 1ml of unknown B and put in a magnetic stirring bead in the round bottom flask at 0 degree temperature. Place the round bottom flask on a hot plate to stir for 30 minutes and also leave a needle on the round bottom cover top to release gases evolved. Remove the round bottom flask after 30 minutes and undergo a TLC test. Transfer the mixture into a 50ml beaker, add ice to the beaker then add 1.5ml of concentrated HCL followed by 5ml of DCM to the beaker to quench the mixture. Transfer mixture to a separating funnel. Pipette 5-10ml of sodium bicarbonate to the separating funnel and place a stopper on top, tilt the separating funnel upside down, shake it and release gas at the opposite end of the separating funnel repeat this process until all gases are released (repeat process again by adding another 5-10ml of sodium bicarbonate). Collect organic layer into a 50ml conical flask. Add 5-10mls of magnesium sulphate into the separating funnel. Tilt the separating funnel and release gases until no gas is left and again collect the organic layer. NMR and IR are tested. Yield = (0.2682/0.6709)×100= 39.98%.

Results and discussion

On the NMR data there were 4 major peaks. They are 1.88, 1.980, 3.083 and 3.000. They correspond to 1.88 and1.980 are aromatic ring peaks; 3.083 is CH3 group that is attached to the aromatic ring (R attached to aromatic ring) and 3.000 is the C=OCH3 peak. On the IR data there were 3 significant peaks. First peak at 2922.208 which correspond to C-CH3 (R on aromatic ring), second peak at 17100 which correspond to C=O peak and the last peak at 800 which correspond to para substitution aromatic ring. From these results we confirm that our unknown B is toluene due to the presence of CH3 group. Reaction mechanism is attached below: