Acylation Reactions under Microwaves. 3. Aroylation of Benzene and Its Slightly Activated or Deactivated Derivatives

Abstract

Solvent-free aroylation of benzene and its slightly activated or deactivated derivatives has been carried out under microwave (MW) irradiation, in the presence of iron(III) chloride which, in these conditions, shows better activity than other metallic chlorides (in particular, AlCl3). With the more reactive and/or nonvolatile reagents (naphthalene, mesitylene, p-xylene, ethylbenzene, and cumene), expeditious conditions (constant MW power and short reaction time without temperature control) have been used. With the less reactive and/or low-boiling reagents (benzene, toluene, and fluoro-, chloro-, and m-dichlorobenzene), the rise in temperature and the lengthening of the reaction time have been controlled by sequential MW irradiations. MW has preferential interactions with polar species involved in the reaction, the aroyl chloride and the aryl ketone, especially with their FeCl3-complexed forms. However, a MW nonthermal effect has not been observed when identical temperature gradients are produced by classical heating and MW irradiation, either for the yield or for the regioselectivity of the reaction.