THE THERMAL DECOMPOSITION OF AZOMETHANE: I. EFFECT OF ADDED OLEFIN AND NITRIC OXIDE

Abstract

The addition of ethylene and propylene reduces the rate of azomethane decomposition as measured by the rate of nitrogen production, and also reduces the ratio CH₄/N₂ in the products, but the reduction in the value of both quantities is different for each of the two olefins. In 100% decomposition, ethylene and propylene both increase somewhat the ratio (nitrogen recovered)/(azomethane decomposed). These results are interpreted to mean that there is in fact a short chain in the pyrolysis, but that ethylene and propylene are unsuitable inhibitors.The addition of a few millimeters of NO reduces the rate to a minimum which is lower than that with added propylene or ethylene (apparent chain length 2 to 3), but further addition of NO increases the rate again. Identical result is obtained in a packed vessel. The yield of methane, ethane, and ethylene is reduced to almost zero with a sufficient amount of NO. The ratio (NO consumed)/(nitrogen produced) reaches the value of two in the neighborhood of the rate minimum. It is concluded that the net inhibited rate, i.e. rate corrected for the stimulatory effect of NO, refers to the initial unimolecular process CH₃N₂CH₃ → 2CH₃ + N₂. The rate as well as the activation energy of this process is found to be pressure dependent.It is shown by the use of the isotopic nitric oxide ¹⁵NO that about one-half of the rate increase at higher NO pressures is due to nitrogen produced from NO. The remainder of the rate increase is accounted for by a NO-induced decomposition of azomethane.