Reaction between haloaromatics over a CuHZSM-5 zeolite—Mechanistic Study

Summary The reaction between haloaromatic compounds (RX and X: R=−F, −Cl, −CH 3 , −CF 3 ; X=−Cl, −Br, −I) was studied in gas phase (400°C, atmospheric pressure) in a flow microreactor in the presence of a 2 wt% Cu-HZSM-5 catalyst. In most cases a highly selective ipso exchange of halogen atoms was obtained except with fluorine which was completely unreactive. The kinetic study of the reaction between bromobenzene and 3-chlorofluorobenzene showed that the bromo compounds are more strongly adsorbed than chloro compounds and inhibit the reaction. The reactivity sequence of the halogen leaving-group (−Br>−I>−Cl≫−F) as well as the positive value of the ρ reaction constant are in favour of a S RN mechanism although a mechanism through aryl copper complexes cannot be excluded.