ACYLATION OF PHENOL WITH ACETIC-ACID OVER A HZSM5 ZEOLITE, REACTION SCHEME

The scheme of the gas phase phenol acylation with acetic acid on a HZS M5 zeolite was established from the effect of contact time (hence of c onversion) on the product distribution. Phenyl acetate and o-hydroxyac etophenone are primary products, O-acylation being much faster than C- acylation. At high conversion, part of the o-hydroxyacetophenone resul ts from the acylation of phenol with phenyl acetate. The formation of p-hydroxyacetophenone which does not occur through phenol acylation in volves the hydrolysis of p-acetoxyacetophenone selectively formed thro ugh the autoacylation of phenyl acetate. The ortho-selectivity of phen ol acylation can be related to a pronounced stabilization of the trans ition state while the para-selectivity of phenyl acetate autoacylation could be due to a steric hindrance to the approach of the acetyl grou p in the ortho-position of phenyl acetate.