Pyrolysis of dimethyl peroxide

By using isobutane (t-BuH) as a radical trapit has been possible to study the initial step in the decomposition of dimethyl peroxide (DMP) over the temperature range of 110–140°C in a static system. For low concentrations of DMP (2.5 × 10^?5?10^?4M) and high pressures of t?BuH (～0.9 atm) the first-order homogeneous rate of formation of methanol (MeOH) is a direct measure of reaction (1): documentclass{article}pagestyle{empty}begin{document}${rm DMP}mathop to limits^1 2{rm Me}mathop {rm O}limits^{rm .},{rm Me}mathop {rm O}limits^{rm .} + t{rm - BuH}mathop to limits^4 {rm MeOH} + t{rm -}mathop {rm B}limits^{rm .} {rm u}$end{document}. For complete decomposition of DMP in t-BuH, virtually all of the DMP is converted to MeOH. Thus DMP is a clean thermal source of Medocumentclass{article}pagestyle{empty}begin{document}$mathop {rm O}limits^{rm .}$end{document}. In the decomposition of pure DMP complications arise due to the H-abstraction reactions of Medocumentclass{article}pagestyle{empty}begin{document}$mathop {rm O}limits^{rm .}$end{document} from DMP and the product CH₂O. The rate constant for reaction (1) is given by k₁ = 10^15.5?37.0/θ sec^?1, very similar to other dialkyl peroxides. The thermochemistry leads to the result D(MeO? OMe) = 37.6 ± 0.2 kcal/mole and /H(Medocumentclass{article}pagestyle{empty}begin{document}$mathop {rm O}limits^{rm .}$end{document}) = 3.8 ± 0.2 kcal/mole. It is concluded that D(RO? OR) and D(RO? H) are unaffected by the nature of R. From ΔS and A₁, k₂ is calculated to be 10^10.3±0.5 M^?1· sec^?1: documentclass{article}pagestyle{empty}begin{document}$2{rm Me}mathop {rm O}limits^{rm .} mathop to limits^2 {rm DMP}$end{document}. For complete reaction, trace amounts of t-BuOMe lead to the result k₂ ～ 10⁹ M^?1 ·sec^?1: documentclass{article}pagestyle{empty}begin{document}$2t{rm - Bu}mathop to limits^5$end{document} products. From the relationship k₆ = 2(k₂k_5a)^1/2 and with k_5a = 10^8.4 M^?1 · sec^?1, we arrive at the result k₆ = 10^9.7 M^?1 · sec^?1: documentclass{article}pagestyle{empty}begin{document}$2t{rm - u}mathop {rm B}limits^{rm .} to (t{rm - Bu)}_{rm 2}{rm,}t{rm -}mathop {rm B}limits^{rm .} {rm u} + {rm Me}mathop {rm O}limits^{rm .} mathop to limits^6 t{rm - BuOMe}$end{document}.