Friedel-Crafts Reaction

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The purpose of this experiment is to perform a Friedel-Crafts reaction of ferrocene. Friedel-Crafts reactions are examples of electrophilic aromatic substitution reactions in which the electrophile is a carbocation or an acylium ion. These reactions form a carbon-carbon bond and allows for either an alkyl or acyl group to be substituted onto an aromatic ring. Figure 1 shows the general mechanism for the Friedel-Crafts acylation of benzene. First, the alkyl halide reacts with a strong Lewis Acid catalyst, usually aluminum chloride, to form a complex, which will then lose the halide to the Lewis acid to give the electrophilic acylium ion. The ion, stabilized by resonance, will react with the p-electrons from a double bond in benzene (acting as a nucleophile) and form the cyclohexadienyl cation intermediate and the tetrachloroaluminate anion. The anion then acts as a base to remove a proton from the ring and reform the initial Lewis acid. The ring regains its aromaticity and the product, an aromatic ring with an acyl substituent is fully synthesized.…show more content…
Instead of using a simple benzene derivative as a reactant, the substrate being used is ferrocene, which consists of a central iron atom bounded or sandwiched between two cyclopentadienyl rings. This synthesis also involves greener reagents. As stated above, aluminum chloride is often used as a strong Lewis acid catalyst to start the reaction. However, it is corrosive and can give off considerable quantities of acidic and toxic wastes. Since ferrocene is highly reactive (due to its two cyclopentadienyl rings), AlCl3 can be replaced with a more benign catalyst, phosphoric acid. This reaction will also use acetic anhydride in place of an alkyl halide. Figure 2 shows the mechanism for this

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