The Role of an Acid in the Decomposition of Mixed Benzoyl-Substituted Phosphonium-Iodonium Ylide

Mixed phosphonium-iodonium ylides allow the synthesis of not easily accessible and novel heterocyclic compounds. Photoinitiated reactions of phosphonium-iodonium ylides with acetylenes proceed with induction time and are catalyzed by acids, the acids formed in the reaction among them. The kinetic peculiarities of the reaction between the benzoyl-substituted phosphonium-iodonium ylide and trifluoroacetic acid were studied by UV-visible spectrophotometry. The kinetic parameters of the reaction were determined. The mechanism of the autocatalysis by acids has been proposed, which involves the formation of a protonated form of the ylide active in the decomposition into radical cations. The more active decomposition of the protonated ylide is confirmed by theoretical thermochemical calculations.