Mechanistic Studies of Fluorodecarboxylation with Xenon Difluoride

Article abstract of DOI:10.1021/jo00055a026

The reaction of xenon difluoride with primary carboxylic acids involves a free-radical mechanism.Trifluoroacetic acid (1) decarboxylates in benzene to give (trifluoromethyl)benzene (2). 6-Hexenoic acid (3) produces a free radical in a radical clock reaction in which the k_abs (25 deg C) for XeF2 was determined as 1.1 * 10⁶ M^-1 s^-1.The primary radical from hexanoic acid was spin-trapped to give ESR signals diagnostic for the alkyl radical.Secondary acids were shown to proceed through a trivalent intermediate, but its exact nature was not proven.The acid 6 gave a rearranged product (7) characteristic of carbocations, whereas the diacid 8 gave difluoro compounds without stereoselectivity.The tertiary bicyclic acids 13 and 15 gave products only from solvent hydrogen abstraction strongly indicative of free radicals.