Insights into reactivity patterns of Ag(II)SO4 with respect to fluoro- and trifluoromethyl-substituted aromatics

Abstract

Direct oxidative functionalization of CH bonds is an ongoing chemical challenge. Here we report results of the comparative tests of Ag(II)SO4 reactivity towards 24 selected fluoro- and/or trifluoromethyl-substituted aromatic hydrocarbons with ionization potentials (IP) varying in the 8.15–10.72 eV range. For many of those we observed the oxidative CC coupling reactions and/or O-insertion in the CH bonds. Observed differences in reactivity of organic substrates are explained on the basis of their IP values on one side, free Gibbs energy of the heterolytic CH bond cleavage on the other, as well as impact of the steric hindrance effect of CF3- groups. The electron affinity of the surface of solid Ag(II)SO4 was estimated at ca. 9.3 eV. Interesting Brønsted acid-induced side reaction of the protolytic CF bond activation, followed by conversion of the trifluoromethyl group to esters of hexafluoro-i-propanol or nonafluoro-t-butanol used as reaction medium, has been observed for 1-(trifluoromethyl)naphthalene.