KINETICS AND MECHANISMS OF THE PYROLYSIS OF DIMETHYL ETHER: II. THE REACTION INHIBITED BY NITRIC OXIDE AND PROPYLENE

Abstract

The thermal decomposition of dimethyl ether, inhibited by nitric oxide and by propylene, was studied in the temperature range of 500 to 600 °C. About 1.5 mm of nitric oxide gave maximal inhibition, the rate then being approximately 8% of the uninhibited rate. With propylene, approximately 70 mm gave maximal inhibition, the rate being slightly higher than that using nitric oxide (~12.5% of the uninhibited rate). In both cases the degree of inhibition was independent of the ether pressure. In the maximally inhibited regions both reactions are three-halves order with respect to ether pressure. As the pressure of nitric oxide was increased beyond 10–15 mm, the overall rate increased, and in this region the reaction is first order with respect to both nitric oxide and ether. A 50:50 mixture of CH3OCH3 and CD3OCD3, with enough NO to ensure maximum inhibition, was pyrolyzed. Even at very low percentage decomposition the CD3H/CD4 ratio was approximately the same as that in the uninhibited decomposition, proving that the inhibited reaction is largely a chain process. Detailed inhibition mechanisms are proposed in which the inhibitor is involved both in initiation and termination reactions.