Phosphorylformonitrile oxides as spin traps for carbon-centered free radicals: co-formation with radicals in the generation of nitrile oxides from C-phosphorylformohydroximoyl halides in the presence of alcohols or ethers

Abstract

One-electron oxidation of the oximes R2P(=O)C(=NOH)X (X = Cl or Br) generates the nitrile oxides R2P(=O)C+=NO−, which serve as spin traps for unstable carbon-centered radicals.The latter are generated upon addition of PbO2 to a mixture of formohydroximoyl halide with an alcohol or an ether of the general formula R1OCHR2R3 under the action of atomic chlorine (bromine) released during the generation of nitrile oxide. This gives rise to new, more persistent C phosphoryliminoxyls R2P(=O)C(=NO·)C(OR1)R2R3 (R1, R2, R3 = H, Alk). When primary alcohols (R1 = R2 = H) are used, acyl radicals generated at the initial step of the reaction are also trapped by nitrile oxides to give C-acyl-C phosphoryl iminoxyl radicals R2P(O)C(=NO·)C(=O)R3. Hyperfine coupling constants for more than 20 C-phosphoryl-iminoxyls existing in solutions as mixtures of Z- and E-isomers were determined.The effect of the structure of the primary radical (length of the carbon chain, degree of branching, the presence of a ring, and its size) on the radiospectroscopic characteristics of new C-phosphoryliminoxyl radicals was studied.