Limits to oxidation of organic substrates. SET oxidative processes of commonly used solvents as revealed through the photochemical reaction with 1,2,4,5-benzenetetracarbonitrile

The chemical reactivity upon single electron transfer of some common solvents has been explored This has been obtained by using photo excited benzene-1,2,4,5-tetracarbonitrile (TCB) as the oxidant. Under this condition acetonitrile, isobutyronitrile, methanol and trifluoroethanol all undergo alpha-deprotonation from their radical cations giving alkyl radicals which are trapped by TCB- and yield alkylbenzenetricarbonitriles or products derived from them. The reaction of the two aliphatic nitriles occurs only in the presence of protic additives, and is accompanied by a different fragmentation leading to methyl (or respectively isopropyl) radicals. Trifluoroacetic acid decarboxylates, probably via oxidation of the anion. TCB irradiation in neat methanol (rather than in MeOH-MeCN mixtures) leads to protic addition onto the cyano group, finally giving dicyanoindoles.