The thermal decomposition of the methoxymethyl and ethyl radicals.

Abstract

The mercury-photosensitized decomposition of dimethyl ether ws investigated from 200° to 300°C and over the pressure range of 3 to 600 mm Hg. Measurements were made of the intial rates of formation of the products of reaction, which are CO, H2, C2H6, CH 4, CH3OC2H5 and CH3OCH 2CH2OCH3. It is concluded that the primary step involves a C-H split; there is no evidence for a primary C-O split. The decomposition of the methoxymethyl radical, generated in the mercury-photosensitized decomposition of dimethyl ether, has been investigated over the temperature range 200 to 300°C and the pressure range 3 to 600 mm Hg. The radical decomposes to give a formaldehyde molecule and a methyl radical. The effects of pressure and temperature on the first-order rate coefficient for the decomposition of the methoxymethyl radical have been examined in detail. As part of the study of the mecury-photosensitized decomposition of dimethyle ether, the combination of methyl radicals has been investigated in the temperature range 200 to 300°C and at pressures between 3 and 300 mm HG. The pressure dependence agrees qualitatively with that observed by others, but occurs at somewhat higher pressures. The results for the mecury-photosensitized decomposition of dimethyl ether have been analzed in order to obtain information about the combination of methyl radicals with methoxymethyl radicals in the temperature range 200 to 300°C and at pressures from 3 to 600 mm Hg. A kinetic study has been made of the pyrolysis of 1,2-dimethoxyethane, CH3OCH2CH2OCH3, using toluene as a radical scavenger. The kinetics of the thermal decompostion of the ethyl radical to give an ethylene molecule and a hydrogen atom was studied over the pressure range of 4 to 650 mm Hg and the temperature range 400 to 500°C; the mecury-photosensitized decomposition of ethane was used to generated the ethyl radical. The results lead to a value of 98.1 kcal. per mole for the bond dissociation energy D(C2H3-H). (Abstract shortened by UMI.)