For Friedel Crafts acylation of ferrocene 1. Acetic anhydride is the “excess” re

Question

For Friedel Crafts acylation of ferrocene

1. Acetic anhydride is the “excess” reagent ( ferrocene is the limiting reagent ) in this experiment. In what step of the work-up procedure is this excess reagent destroyed? What product is obtained after it is destroyed?

2. Why can hexanes be used to elute the unreacted ferrocene? Why does acetylferrocene not move down the column along with ferrocene?

3. If you wanted to modify the experimental procedure to synthesize diacetylferrocene, what changes might you consider? Consider each of the following:

Stoichiometry

Reaction conditions

Purification of final product by column chromatography

Explanation / Answer

1. In the work up procedure by addition of water the excess acetic anhydride is queched. By reacting with water acetic anhydride is converted to acetic acid.

2. Ferrocene is a non polar compound when compared with acetyl ferrocene. When you elute the column with only hexane, the non polar unreacted ferrocene only comes out of the column. Acetyl ferrocene is more polar compound and the polarity of the hexane is not sufficient to elute the acetyl ferrocene out of the column.

3. If you wanted to modify the experimental procedure to synthesize diacetylferrocene,

The stoichiometry of acetic anhydride should be doubled means you have to use two equivalents of acetic anhydride to make diacetylferrocene.

In the reaction conditions the reaction mixture has to be kept in heating conditions to ensure the second acetylation reaction happens in acetylferrocene.

In the purification of diacetylferrocene by column chromatography, one has to increase the polarity of the eluting solvent in the column as the diacetylferrocene is more polar than acetylferrocene.

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