AbstractThe decomposition of the cumene, tetralin, andt‐butylhydroperoxides in the presence of zinc diisopropyl dithiophosphate and of radical‐type inhibitors has been studied. A poisoning of the catalyst and a further change into an inactive form has been found. This leads to an inhibition of the overall decomposition rate of the hydroperoxides. It is suggested that the accumulation of RO* radicals arising from the thermal decomposition of the hydroperoxides reactivates the inactive catalyst. Based on the consumption of phenyl‐β‐naphtylamine and the stable 2,2,6,6‐tetrametylpiperidinoxyl radical, a homolytic decomposition of the hydroperoxides has been shown to take place. The rate of decomposition of the hydroperoxides to free radicals is 103times slower than that leading to molecula