SUBSTITUENT EFFECT ON THE THERMAL-DECOMPOSITION OF ACETAL HYDROTRIOXIDES - POLAR AND RADICAL DECOMPOSITION PATHS

Low-temperature ozonation of aliphatic and aromatic acetals leads to oxygen-rich intermediates, acetal hydrotrioxides 1-3, the NMR spectra of which show two absorptions at δ 13 ppm downfield from Me4Si. Decomposition of these compounds, which affords among other products singlet oxygen and peroxides, involves nonradical and radical processes. The kinetics of decomposition has been studied by NMR spectroscopy and activation parameters have been determined. Electron-withdrawing substituents in 3 accelerate decomposition in diethyl ether while electron-donating groups retard it (Hammett ρ value 1.2 ± 0.2). Considerable charge separation in the transition state for the decomposition has been proposed. © 1979 American Chemical Society.