A new environment-friendly synthesis of hydroxyphenylalkylketones was developed operating in vapor phase and using a commercial pentasil-type zeolite, obtaining both high conversion values of the phenylacetate feed and high selectivity in the ortho-hydroxyacetophenone, together with a low amount of by-products. Furthermore, good catalytic performances were also obtained with longer chain esters. The peculiar features of this catalyst-either as such or in the presence of finely ground Al2O3 as binder-were investigated by FT-IR spectroscopy, as such or using a non-hindered (acetonitrile) and a hindered nitrile (pivalonitrile) as probes, with a view to explaining its unusual behavior. These data suggest that the catalyst is a modified HZSM5 zeolite, probably externally covered by a layer of terminal silanols, with lowering of acidity and formation of small amounts of defects represented by enlarged channels. The alumina binder does not hinder the access to cavities, but seems to limit the number of defects or their availability. (C) 2003 Elsevier B.V. All rights reserved.