Oxidation of trimethylsilyl radicals by N2O: A mechanistic study

The reaction of Me3Si (Me drop CH3) radicals with N2O has been studied by a nalysis of the end products of the mercury-sensitized photolysis of N2O wit h Me3SiH. The main products found were N-2, Me3SiSiMe3, Me3SiOSiMe3, and Me 3SiOH. The influence on both major and minor products of reactant pressure, different scavenger and quencher molecules, temperature, and the reactor s urface permits the derivation of a reaction mechanism and identification of the intermediates involved. The most important steps comprising the mechan ism are oxygen abstraction from N2O by Me3Si with formation of Me3SiO and a chain propagation step, the reaction of Me3SiO and Me3SiH with formation o f Me3SiOH and Me3SiO. Although the precise nature of the last step is unkno wn, it is a multistep reaction. Me2SiO radicals also undergo combination wi th Me3Si radicals. Self-combination under formation of a peroxide does not occur. Vibrationally excited species emerge in Si-O bond-forming processes, and a number of minor products stem from unimolecular decomposition of the se excited species. The rate constant of O atom abstraction from N2O (react ion 5) relative to Me3Si radical combination (reaction 4) is given by k(5)/ k(4)(1/2) = (6.5 +/- 1.3) x 10(-12) cm(3/2) s(-1/2) at room temperature. An activation energy of E-A(5) = 23 +/- 1 kJ mol(-1) is obtained from experim ents in the temperature range 295-520 K.