[Orgo Lab 2] The Friedel-Crafts Reaction: Acetylation of Ferrocene

Videos You Should Watch for this Lab: Recrystallization:    • [Orgo Lab] Recrystallization of Acetanilide   Thin-Layer Chromatography:    • [Orgo Lab] CSI Thin-Layer Chromatography   The Friedel-Crafts reaction, developed by Charles Friedel and James Crafts in 1877, is a substitute reaction of a benzene ring. As seen in this example reaction scheme, an acyl group is attached to a benzene ring via the Friedel-Crafts method. In this reaction, aluminum chloride, AlCl3, as a catalyst, activates an acid chloride. The acid chloride reacts and forms a complex with AlCl3. A chlorine of the acid chloride is then lost to the aluminum chloride, which gives an acylium ion and a tetrachloro aluminate anion. The acylium ion is an electrophile that is then attacked by the p electrons of the aromatic carbon double bond. The result is a cyclohexadienyl cation intermediate. The proton of the carbon bearing the acyl group is removed by the tetrachloro aluminate anion. This step reforms the carbon double bond, yielding the acylated aromatic ring, with hydrochloric acid as the side product. Note that AlCl3 is re-generated after the reaction finishes. Today, we are going to perform the Friedel-Crafts reaction using ferrocene instead of benzene. This is because ferrocene contains more reactive cyclopentadienyl anion rings. Therefore, we can use milder and greener reagents than normal for the Friedel Crafts reaction. Instead of an acid chloride, we will use an acid anhydride. Instead of AlCl3, we will use phosphoric acid as the catalyst. Phosphoric acid will protonate the acetic anhydride to give the electrophile that then reacts with the aromatic cyclopentadienyl anion. The result is a cyclopentadienyl intermediate. The proton of the carbon bearing the acyl group is removed by the dihydrogen phosphate anion formed earlier. This produces the acylated cyclopentadienyl anion, with phosphoric acid regenerated in the end. Here is the product we are going to obtain today, acetylferrocene. Besides using milder and greener reagents, another green feature of this atypical example of the Friedel Crafts reaction is that no solvent is used other than the acetic anhydride reagent. Under these mild conditions, the aromatic rings undergo only monosubstitution. Video Production: Dr. Xu's Research Group (Dr. Xu, Han, Emma, Nhu, and Emily). Contents: 0:00 - Introduction 3:28 - Acetylation of ferrocene 5:53 - Neutralization 7:33 - Recrystallization of acetylferrocene 9:36 - Analysis of products via TLC