Oxidation of Trimethylsilyl Radicals by N₂O:  A Mechanistic Study

Abstract

The reaction of Me 3 Si (MetCH 3 ) radicals with N 2 O has been studied by analysis of the end products of the mercury-sensitized photolysis of N 2 O with Me 3 SiH. The main products found were N 2 , Me 3 SiSiMe 3 , Me 3 SiOSiMe 3 , and Me 3 SiOH. The influence on both major and minor products of reactant pressure, different scavenger and quencher molecules, temperature, and the reactor surface permits the derivation of a reaction mechanism and identification of the intermediates involved. The most important steps comprising the mechanism are oxygen abstraction from N 2 O by Me 3 Si with formation of Me 3 SiO and a chain propagation step, the reaction of Me 3 SiO and Me 3 SiH with formation of Me 3 SiOH and Me 3 -Si. Although the precise nature of the last step is unknown, it is a multistep reaction. Me 3 -SiO radicals also undergo combination with Me 3 Si 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 these excited species. The rate constant of O atom abstraction from N 2 O (reaction 5) relative to Me 3 Si radical combination (reaction 4) is given by k 5 /k 4 1/2 ) (6.5 ( 1.3) × 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 experiments in the temperature range 295-520 K.

Nitrous Oxide as a 1,3-Dipole: A Theoretical Study of Its Cycloaddition Mechanism

“…The catalytic decomposition of nitrous oxide on various surfaces 5 as well as the dissociative electron attachment have widely been investigated . Reactions of N 2 O with radicals giving N 2 has also been studied …”

The H/(CH3)3SiH/C2H4Reaction System and the Addition of (CH3)3Si to Ethene. An End-Product Study

“…The authors added NO as a radical scavenger to their reaction mixture to avoid secondary reactions between the radicals formed and the reactants C 2 H 4 and Me 3 SiH. By adding NO, however, they initiated what they tried to avoid: Me 3 Si radicals react with NO with the formation of Me 3 SiO, which reacts further with Me 3 SiH to form Me 3 SiOH, in this way starting a chain of small length.…”

“…This actinometer has been checked versus the cis -butene-2 actinometer (Φ( trans -butene-2) = 0.5), and the values of the two actinometers agreed within 1.6% . The light intensity determined actinometrically was shown to depend linearly on the measured absorption in the range 0−80% …”