Question

Friedel-Crafts Acylation of Ferrocene

H3PO4 DISCUSSION 1. This reaction is done with a 10-fold excess of acetic anhydride, yet the dominant product of the reaction is the mono-acylated compound. Very little 1,1'-diacetylferrocene is formed. a. Why? b. What conditions are necessary to form 1,1'-diacetylferrocene as the main product? c. Why does 1,3-diacetylferrocene not form under these conditions? 2. During workup of the product, water reacts with the excess acetic anhydride to give what side product(s)?

Answer 1

a) Generally, ferrocene is more reactive than aromatic compounds in electrophilic substitution reactions. So, mild conditions are enough for monoacylation (H3PO4 is milder compare to AlCl3). After monoacylation, it becomes somewhat electron-deficient and also these are milder conditions. So, it can not go diacylation.

b) It needs somewhat harsh conditions after a monoacylation. The suitable conditions are AlCl3 and acetic anhydride to get the diacylated product.

c) After monoacylation on 1st ring, it becomes electron-deficient, it does not allow for acylation on same ring at 3 position. So, it alow to acylate at 1st position of 2nd ring and results 1, 1' diacylation.

2 Water reacts with excess acetic anhydride and forms acetic acid as side product.