Thermal Decomposition of 2,2-Bis(t-butyldioxy)alkanes

The thermal decomposition of 2,2-bis(t-butyldioxy)propane (1a) has been studied in cumene. The activation parameters obtained by the thermolysis of la are ΔH=145.6kJ mol−1 and ΔS=47.3 J K−1 mol−1. The decomposition products of 1a are acetone, t-butyl alcohol, t-butyl hydroperoxide, t-butyl peracetate, t-butyl 1-methyl-1-phenylethyl peroxide, and bis(1-methyl-1-phenylethyl). The peroxyacetal cleaves homolytically at one of dioxy bonds to yield an intermediate alkoxyl radical with α-t-butyldioxy group, which decomposes subsequently to t-butyldioxyl and methyl radicals via β-elimination. The thermal decomposition of 2,2-bis(t-butyldioxy)butane and 2,2-bis(t-butyldioxy)-3-methylbutane have also been examined. Relative rates of β-elimination of radicals from alkoxyl radicals are concluded to be isopropyl: ethyl:t-butyldioxyl: methyl=133:33:7:1, revealing a facile scission of dioxyl radical.