Acylation reactions under microwaves. 3. Aroylation of benzene and its slightly activated or deactivated derivatives

Solvent-free aroylation of benzene and its slightly activated or deactivate d derivatives has been carried out under microwave (MW) irradiation, in the presence of iron(III) chloride which, in these conditions, shows better ac tivity than other metallic chlorides tin particular, AICl(3)). With the mor e reactive and/or nonvolatile reagents (naphthalene, mesitylene, p-xylene, ethylbenzene, and cumene), expeditious conditions (constant MW power and sh ort reaction time without temperature control) have been used. With the les s reactive and/or low-bailing reagents (benzene, toluene, and fluoro-, chlo ro-, and m-dichlorobenzene), the rise in temperature and the lengthening of the reaction time have been controlled by sequential MW irradiations. MW h as preferential interactions with polar species involved in the reaction, t he aroyl chloride and the aryl ketone, especially with their FeCl3-complexe d forms. However, a MW nonthermal effect has not been observed when identic al temperature gradients are produced by classical heating and MW irradiati on, either for the yield or for the regioselectivity of the reaction.