Mechanisms of Heterogeneous Processes in the System SiO_2 + CH_4: III. Products of >Si

摘要

The methods of optical, ESR, and IR spectroscopy were used to obtain data on the structure and mechanism for the formation of the products in the reaction of dioxasilirane groups (SiO)_2SiO_2 (DOSG) stabilized on the silica surface. Depending on the regime of the reaction (temperature and methane pressure), the process is accompanied by the formation of various products: methoxy (OCH_3) and ethoxy (OC_2H_5) groups. The process mechanism is elucidated: this is a free-radical reaction in which paramagnetic sites are generated in the reaction between DOSG and methane molecules. The formation of final products is due to the reactions Si(O~·)(OCH_3) + CH_4 → >Si(OH)(OCH_3) + ~·CH_3 and >Si(O-~·CH_2)(OH)+~·CH_3 → >Si(OH)(OC_2H_5). The ratio of the rate constants of methyl radical addition to (SiO)_2Si: and (SiO)_2SiO_2 at room temperature was determined experimentally (4.6±1.0).