Trifluoromethyl radicals have become en vogue and advanced to being the key intermediates in many modern trifluoromethylating protocols. Several precursors are commercially available, each featuring its (dis)advantages. We opted to evaluate Langlois’ reagent, Togni’s reagent, trifluoroacetate and CF3I by means of pulse radiolysis: after irradiating an aqueous sample the reaction of primary radiolysis products (H●, HO●, e-aq) allow to study oxidations, single electron reductions and addition reactions on the μs-time scale. Furthermore, we investigated whether the addition of the perceivably highly electrophilic CF3 radical to an aromatic system is reversible or not (most published mechanistic schemes suggest irreversibility). In our experiments, both the methyl and the trifluoromethyl radical showed behavior best interpreted by invoking a reversible addition to our aromatic probe HisNH2. Specifically, the absorbance 4 μs after irradiation changes non-linearly with the concentration of the probe. Furthermore and in accordance to the expected higher electrophilicity of the fluorinated radical species we find: K(CF3) &gt; K(CH3). We will showcase the experimental setup, data treatment and present figures for these equilibrium constants of interest.

CF3 radical precursors and their reactions with primary radiolysis products – reversible addition of F3C● to an aromatic model system

253rd National Meeting (2017)

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