Divergent role of PIDA and PIFA in the AlX (X = Cl, Br) halogenation of 2-naphthol: a mechanistic study.

The reaction mechanism for the chlorination and bromination of 2-naphthol with PIDA or PIFA and AlX (X = Cl, Br), previously reported by our group, was elucidated via quantum chemical calculations using density functional theory. The chlorination mechanism using PIFA and AlCl demonstrated a better experimental and theoretical yield compared to using PIDA. Additionally, the lowest-energy chlorinating species was characterized by an equilibrium of Cl-I(Ph)-OTFA-AlCl and [Cl-I(Ph)][OTFA-AlCl], rather than PhICl being the active species. On the other hand, bromination using PIDA and AlBr was more efficient, wherein the intermediate Br-I(Ph)-OAc-AlBr was formed as active brominating species. Similarly, PhIBr was higher in energy than our proposed species. The reaction mechanisms are described in detail in this work and were found to be in excellent agreement with the experimental yield. These initial results confirmed that our proposed mechanism was energetically favored and therefore more plausible compared to halogenation via PhIX.