Radicals generated by the heterogeneous decomposition of peracetic acid studied by electron spin resonance spectroscopy

Abstract

Peracetic acid, a branching agent commonly associated with low temperature organic oxidations, is decomposed in flowing conditions over extensive surfaces coated with KCl, KBr or BaBr₂ at temperatures in the range 300–560 K.

Free radicals generated from the surface decomposition are pumped, at low pressure, to a cold finger within the cavity of an e.s.r. spectrometer, where thay are trapped in a solid matrix. Electron spin resonance spectra become more intense as radicals accumulate on the finger. Greater yields accumulate as the temperature of each surface is increased: these yields correspond to increasing extents of decomposition of peracetic acid within its residence time at each surface. Surface activity leading to generation of radicals varies roughly in the concentration ratios KCl : KBr : BaBr₂= 3 : 2 : 1. Beyond the temperature at which all peracetic acid is decomposed, the radical yields fall, indicating that some radicals are removed by surface termination.

Evidence for the surface generation of free radicals suggests that surface reactions may contribute to chain branching in some organic oxidations.