Substituent Effects in the Decomposition of t-Alkyl t-Butyl Peroxides

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The decomposition rates and products of various t-alkyl t-butyl peroxides were examined in cumene at several temperatures. The decomposition of these peroxides took place homolytically, depending on the structure of the t-alkoxyl moieties (RC(CH3)2–O), and was retarded in the order: R=(CH3)3CCH2>(CH3)2CH>CH3CH2CH2>PhCH2>CH3CH2>ClCH2>CH3. The rate constants for the electron-donating alkyl substitutents at 150 °C are correlated very well to a Taft equation (logkd=−10.93 Σσ*−6.61 (correlation coefficient of 0.9501)), which is fairly different from the equation logkd=−10.131 Σσ*−3.422 for electorn-withdrawing polar substituents. From this correlation and a product analysis, the nature of the polar character at the transition state of the decomposition is discussed.