Friedel-Crafts Acylation of Ferrocene: Acetylferrocene Last revision: 08/21/12
Adapted from JR Mohrig, CN Hammond, TC Morrill, and DC Neckers Experimental Organic Chemistry (A Balanced Approach: Macroscale and Microscale) 1999, WH Freeman, NY 189-194.
Background This experiment has two purposes. The first is to explore Friedel-Crafts acylations of aromatic molecules, and the second is to develop an understanding of column chromatography as a tool for separating organic substances. Friedel-Crafts alkylation and acylation reactions are powerful tools for substituting larger, more complex functional groups in place of aromatic protons. In the absence of strongly π-donating activating groups, powerful Lewis acid catalysts such as aluminum chloride must be used. However, activated aromatic compounds will undergo substitution under much milder conditions. Ferrocene is highly activated, so acetylation occurs readily using a mild Brønstead- Lowry acid catalyst. In fact, ferrocene is so reactive to acetylation that a diacetyl derivative normally forms as a minor product.
ferrocene acetic anhydride 1-acetylferrocene 1,1'-diacetyl ferrocene MW 186.04 Ac2O MW 228.08 MW 102.09 mp 85-86 °C Bp 139.5 °C d 1.08 g/mL major product We will perform this reaction under conditions that will not allow the reaction to go to completion. You should have some ferrocene remaining in your reaction mixture, as well as the 1-acetylferrocene product, and perhaps some of the 1,1'-diacetylferrocene (usually a minor product). This situation will allow us to do the column chromatography under conditions where we can readily see the materials separate as they move down the column. Column chromatography allows us to separate materials based on their relative solubility in a solvent (called the mobile phase, usually less polar than the column material) and attractions to a packed solid column (called the stationary phase, usually very polar).
Fe + O
O O 85% H3PO4 (aq) Fe Ac
+ Fe Ac
Cautions Both acetic anhydride and phosphoric acid are corrosive and will cause burns. Handle with care and immediately neutralize and wipe down any spills. Sodium hydroxide is caustic and will cause burns. Handle with care of immediately dilute and wipe down any spills. DAY 1: Synthesis of Acetylferrocene Begin heating a hot water bath to its boiling point using a 100 mL beaker on your stirring hotplate on your lab jack. Eventually, you will need to clamp your glassware above this water bath. Collect a 4 or 5 mL conical vial, an air-cooled condenser, and a drying tube from your microscale glassware kit. Charge the drying tube with calcium chloride, using cotton pieces on either side of it to hold it in place. Attach it to the top of the air condenser. Be sure to grease each ground glass joint and to hold them together using the screw caps! Place 200 mg of dry ferrocene into the conical vial, followed by 2.0 mL of acetic anhydride. Cap the vial with the condenser/drying tube combo and...