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. I n 10070 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 t o 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 t o almost zero with a sufficient amount of KO. The ratio (NO consumed)/(nitrogen produced) reaches the value of two in the neighborhood of the rate minimum. I t is concluded t h a t the net inhibited rate, i.e. rate corrected for the stimulatory effect of NO, refers to the initial unimolecular process C H~N Z C H ZThe rate a s well a s the activation energy of this process is found t o be pressure dependent.I t is shown by the use of the isotopic nitric oxide ISNO that about one-half of the rate increase a t 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.

The thermal decomposition of azomethane. III. Kinetics of the noninhibited reaction

“…Reactions (6) and (24) form essentially the same radical intermediate mentioned in connection with polymerization, so that if reaction (6) and/or (24) is followed by reactions (8) and (14), as is likely, polymer formation follows. Since both 'CHz and CH3 are minor components in the azomethane system compared to 3CHz and A, it is very likely that most of the polymer will be formed by reaction (6) and not reaction (24).…”

“…Since both 'CHz and CH3 are minor components in the azomethane system compared to 3CHz and A, it is very likely that most of the polymer will be formed by reaction (6) and not reaction (24). Reaction (7), in conjunction with reaction (5), amounts to a sort of azomethane-catalyzed recombination of CHZ with CH3.…”

“…Since the latter reaction appears to be the only plausible source of the ethyl radical, it is worthwhile to assess the relative importance of the two alternative modes of disposal of the triplet methylene by examining the relative rates of reactions (6) and (7).…”

“…In fact, as early as 1935, Patat and Sachsse f2] have found it remarkable that although the pyrolysis of azomethane liberates methyl radicals, azomethane itself apparently does not undergo a chain decomposition. While the complex nature of the reaction products became known a few years later [3,4], it took another twenty years before the presence of a chain in azomethane pyrolysis could be demonstrated [5,6]. The various chromatographic peaks were identified by injecting a sample of the pure compound (when available) or by trapping the peak and subjecting it to analysis by mass spectrometry.…”

X-Ray Induced Polymerization of Gaseous Vinyl Chloride. Effect of Additives

“…Oxygen was prepared by pyrolysis of analytical grade KMnO,. Nitric oxide from Matheson was purified further by the method of Forst and Rice (10). Other additives, SFs, NH3, CH3NH2, HCI, and C2H2, obtained from Matheson Company, were purified by trap-to-trap distillation at -185 "C and distilled water was previously degassed by the thawingfreezing technique before its mixing with the monomer.…”