Thermochemistry of the methoxymethyl radical

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.