SolutionsFries Rearrangement
1. Fries rearrangement products
Which products does phenyl acetate give with AlCl3? And 4-methylphenyl propanoate?
Phenyl acetate gives a mixture of 4-hydroxyacetophenone and 2-hydroxyacetophenone: the acyl group moves from the oxygen to the ring ortho or para to the OH. In 4-methylphenyl propanoate the para position is occupied and 1-(2-hydroxy-5-methylphenyl)-1-propanone is obtained.
Low temperatures favor the para product and high temperatures the ortho one, which is stabilized by chelation with aluminum.
2. Fries or Friedel-Crafts
Why is the Friedel-Crafts acylation of phenol not a good way to prepare hydroxyacetophenones?
Phenol is acylated preferentially at the oxygen (giving the ester), and the OH also complexes AlCl3 and deactivates the ring. The Fries rearrangement takes advantage of that ester: it is made first and the acyl group is then transferred to the ring.