Further studies of the pyrolysis of dimethyl ether

Abstract

The pyrolysis of dimethyl ether has been investigated over the pressure range 35 to 400 mm Hg and the temperature range 750 to 820°K in a quartz flask. The results confirm the previous designation of an initial 3/2-order rate relative to Me2O but yield an activation energy of 55.6 kcal. This can be explained if it is assumed that CH3OCH2 is an important chain breaker and that the reaction CH3OCH 2→CH3+CH2O is an energy transfer process in its second-order region. The small catalysis provided by added N2 and CH4 is supporting evidence for this. Further evidence comes from the observed rate of exchange of deuterium gas with Me2O which is now in good accord with calculation. Values of the rate constants for CH 3 radical attack on H2 and D2 are in good agreement with those extrapolated from much lower temperatures. Some new values of rate constants are reported as well as new estimates of frequency factors and activation energies for various chain steps. There is some evidence for heterogeneous disappearance of H atoms at the wall, including a temporary inhibition observed in KClcoated vessels. Small amounts of added O2 have little effect on the rate while C2H4 is a very powerful inhibitor. At 780°K, chain lengths vary from 21 at 25 mm Hg to 84 at 400-mm Hg pressure. They decrease slowly with increasing temperature.