The reaction of t-butyl hydroperoxide with iodosobenzene diacetate and iodosobenzene in methylene chloride and in diethyl ether has been studied quantitatively at -80 to +5°. The results seem to indicate that at - 80° t-butylperoxy radicals are formed and couple in equilibrium to form di-t-butyl tetroxide without the evolution of oxygen. At - 75 to - 65° the tetroxide decomposes to di-t-butyl trioxide as deduced from the amount of oxygen produced. The trioxide seems to be in equilibrium with t-butoxy and t-butylperoxy radicals and, as the temperature rises, the former abstract hydrogen atoms to form t-butyl alcohol while the latter couple and undergo a secondary decomposition at -45° to give oxygen and di-t-butyl trioxide. When the trioxide is generated at -75° in ethyl ether the t-butoxy radicals abstract hydrogen atoms from the solvent and the ether radicals formed trap the t-butylperoxy radicals and produce αaL-t-butylperoxyethylether in almost quantitative yields. The structure of this ether peroxide was confirmed by an independent synthesis. A mechanism was proposed of all the reactions studied. © 1968, American Chemical Society. All rights reserved.