New Advances in Perfluoroalkytation of Aromatics: Products and Mechanism

Sansotera ^a, P. Metrangolo ^a, W. Navarrini ^a, G. Resnati ^a, I. Wlassics ^b

^a Dip-CMIC ”Giulio Natta”, Politecnico di Milano, via Mancinelli 7, 20131 Milan, Italy;

^b R&D Centre, Solvay Solexis, viale Lombardia 20, 20021 Bollate (MI), Italy

E-mail: maurizio.sansotera@polimi.it; walter.navarrini@polimi.it

Thermal decomposition of perfluorodiacyl peroxides in the presence of aromatic compounds leads to the synthesis of perfluoroalkylated aromatic derivatives. C₃ and C₄-perfluorodiacyl peroxides have been synthesized starting from C₃ and C₄-perfluoroacyl halides with H₂O₂ in alkaline conditions and have been employed in reactions with several aromatic substrates. The capability of perfluorodiacyl peroxides to generate perfluoroalkyl free radicals is at the basis of the perfluoroalkylation process. Perfluoroalkyl radical reacts with the aryl via an electron-transfer propagation process. During the formation of the perfluoroalkylated intermediate the aromatic substrate loses its aromaticity and another molecule of peroxide oxidizes the intermediate. Finally a proton removal restores the aromaticity. Competitive mechanistic pathways are responsible for the perfluoroalkyl radical formation: primarily the concerted dissociation with a three-bond fission, and secondarily the stepwise decomposition through primary homolytic cleavage of O-O peroxidic bond and subsequent decarboxylation. Stability of the oncoming radicals and temperature are the important parameters to discriminate the decomposition pathway. The analyses of reaction main-products and by-products allowed to draw a more complete mechanism pathway that can be applied to the whole family of aromatic compounds.