This experiment focuses on the Friedel-Crafts reaction - a powerful, widely used method of carbon-carbon bond synthesis that proceeds by the mechanism of electrophilic aromatic substitution. Traditionally, the electrophile is generated by the reaction of an alkyl halide, acyl halide, or acid anhydride with a stoichiometric amount of a strong Lewis acid, such as aluminum chloride. Also, the solvents used most often for Friedel-Crafts reactions include methylene chloride and carbon disulfide. Conventional methods for this reaction thus employ hazardous organic solvents and lead to the generation of large amounts of acidic and aluminum-containing waste.
In this greener approach, ferrocene is acylated using the more benign system of phosphoric acid and acetic anhydride in place of the usual, more vigorous acylation reagent generated from aluminum chloride and acetyl chloride. Furthermore, no organic solvents are used, although acetic anhydride is present in excess and may function as a reaction solvent. In addition to being a greener process, this method also leads to a cleaner product, since under these milder acylation conditions the amount of diacetylferrocene is reduced relative to conventional methods. The link to the laboratory procedure includes both pre- and post-lab questions.
Summary prepared July 2005 by James M. Hanna, Jr., Department of Chemistry, Physics, and Geology at Winthrop University.
Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 225-230.