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. The rate coefficient shows a pressure dependence over the full pressure range studied. The order of the decomposition is about 1.4 at the middle of the pressure range studied, with a lower order at higher pressures and a higher order at lower pressures. At 100 mm Hg the observed activation energy for the decomposition of the methoxymethyl radical is 24.8 kcal/mole.The first-order and second-order rate coefficients, k∞ and k0, corresponding to the limiting conditions of high pressures and low pressures respectively, have been evaluated as [Formula: see text]Kassel integrations have been carried out for the methoxymethyl radical and have been fitted to the experimental data. It is concluded that 8 or 9 normal modes contribute to the energization of the radical. The rate coefficient is increased by the presence of carbon dioxide, but carbon dioxide has a lower efficiency than dimethyl ether for the transfer of energy in the energization process.

The kinetics of the thermal decomposition of the ethyl radical to give an ethylene molecule and a hydrogen atom were studied over the pressure range 4 to 650 mm Hg and the temperature range 400 to 500 °C; the mercury-photosensitized decomposition of ethane was used to generate the ethyl radical. The unimolecular decomposition of the ethyl radical was found to be pressure dependent over the entire range of pressures studied, with the order of reaction varying from 1.6 for the lowest pressures to 1.4 at the highest pressures. The extrapolated high-pressure and low-pressure rate constants for the decomposition of the ethyl radical are given by [Formula: see text] [Formula: see text]A best fit of the Kassel equation to the observed pressure dependence shows that s = 8 for this reaction. The results lead to a value of 98 1 kcal/mole for the bond dissociation energy D(C2H5—H). The heat of formation of the ethyl radical was calculated to be 30.0 and 26.2 kcal/mole for 0 °K and 25 °C respectively.

A kinetic study has been made of the pyrolysis of 1,2-dimethoxyethane, CH3OCH2CH2OCH3, using toluene as a radical scavenger. The initial step involves the C—C split, and there are no chains; the activation energy of 71.3 kcal/mole thus corresponds to the dissociation energy of the C—C bond. The heat of formation of CH3OCH2CH2OCH3 has been found to be −81.4 kcal/mole, and these values lead to −5.0 for the heat of formation of the CH3OCH2 radical and 91.1 for the dissociation energy of CH3OCH2—H.Support for these values is provided by the results of a similar study with chloromethyl methyl ether, CH3OCH2C1, for which the C—Cl bond is ruptured in the initial step. Activation energies of 69.3 and 69.9 kcal/mole were found with toluene and propylene as scavengers. With the use of appearance-potential data these values lead to D(CH3OCH2—H) = 92.9 and ΔHf0(CH3OCH2) = −3.2 kcal/mole, with, however, a wider margin of error than for the results with CH3OCH2CH2OCH3.

The mercury-photosensitized decomposition of dimethyl ether was investigated from 200 to 300 °C and over the pressure range 3 to 600 mm Hg. Measurements were made of the initial rates of formation of the products of reaction, which are CO, H2, C2H6, CH4, CH3OC2H5, and CH3OCH2CH2OCH3. It is concluded that the primary step involves a C—H split; there is no evidence for a primary C—O split. Over the range 200 to 300 °C the methoxymethyl radical, CH3OCH2, decomposed to give formaldehyde and a methyl radical, whereas at 30 °C no decomposition of the CH3OCH2 radical was detected. The mass balance is consistent with the mechanism proposed. The homogeneity of the reaction conditions was examined by varying the concentration of mercury in the reaction vessel.

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