The Reactions of Active Nitrogen With Methane and Ethane

Abstract

Reinvestigation of the active nitrogen -methane reaction in the temperature range 45" to 500°C. has confirmed hydrogen cyanide $s the only product, other than hydrogen, formed in measurable amounts. An induction" effect in the hydrogen cyanide production was observed with increase of methane flow rate. This induction decreased with increase of temperature and was shown to be due to concomitant hydrogen atom reactions, since it could be eliminated by addition of hydrogen atoms to the reaction mixture. Reinvestigation of the active nitrogen -ethane reaction over the temperature range -100" to 475OC. also confirmed hydrogen cyanide to be the only measurable product, other than hydrogen, of that reaction. There was some indication that an induction effect was present with ethane, as with methane, and it may be concluded tentatively that both reactions are carried substantially by hydrogen atom reactions. INTRODUCTIONIn a previous study in this laboratory (7), it was observed t h a t the Arrhenius plot for the reaction of active nitrogen with ileopentane showed a marked change of slope, indicative of two activation energies in the range of temperatures used. While there was some reason to believe that this behavior might be due to two reactive species in active nitrogen, one of which is almost certainly atomic nitrogen (4, 5), there remained the possibilities that it resulted from concomitailt hydrogen atom reactions or from different rates of attack by a single species in active nitrogen a t the primary and quaternary carbon atoms in the neopentane molecule. Since methane and ethane are incapable of suffering such different modes of attack, the reactions of active nitrogen with these two hydrocarbons have been reinvestigated over a wider range of conditioils than those used previously (3), in an effort to examine further the possible significance of the two activation energies observed with neopentane. E X P E R I M E N T A LT h e investigations were made with conventional fast-flow techniques. In many experiments with methane, hydrogen atoms were iiltroduced simultaneously with nitrogen atoms. T h e arrangement for doing this is illustrated in Fig. 1, which, with the accompanying legend, serves also to indicate all the essential details of the apparatus currently used in this laboratory for studies on active nitrogen reactions. When necessary, the reaction vessel was surrounded by an electrically heated furnace molded from asbestos or by a plastic vessel to contain an appropriate refrigerant.The nitrogen discharge tube was operated by a 110 v.-5000 v. transformer which fed through a diode rectifier (Raytheon, 866-A-GAA) and a 2000 ohm resistance into two condensers in parallel (each 4 pf., GOO0 v., Aerovox No. 3). 'Manuscript

The Kinetics of the Decay of Nitrogen Atoms as Determined From Chemical Measurements of Atom Concentrations as a Function of Pressure

“…On the other hand, the production of HCN from ethylene under conditions of complete consumption ("cleanup") of active nitrogen (high ethylene flowrates and elevated temperatures), a mode of measurement frequently used in past work (e.g. 17, IS), would likely reflect the atom concentration alone owing to the high activation energy to be expected in most reactions involving excited nitrogen molecules (13).3 HCN production also has the advantages that it is not subject to mechanical failure and, since negligibly small quantities of other nitrogencontaining compounds are formed (20,21), it provides an absolute value of the atom concentration. Production of HCN from ethylene was therefore chosen to measure the N atom concentration and the results were checked using ethane.…”

“…For the reactants ~tsed in the present work the minimum temperatures (about 300" C) were readily obtained from p~tblishecl data (21). Since minimum flowrates, on the other hand, depend on the atom concentration, on the reaction temperature, and on factors peculiar t o each apparatus, the results of past work could not be used.…”

“…The use of chemical measurement of the atom concentrations meant that a fast-flow system of the type employed by Winkler and co-workers (see, in particular, 21,22,23) rather than the much simpler diffusion system of Smith (1) or static system of Rayleigh (7) had to be used (Fig. I).…”

“…The decay tube was followed by a 300-cc spherical reaction vessel F into which the reactant could be injected For personal use only. through jet G. (The arrangement for metering in the reactants has been described elsewhere (21).) The reaction vessel was surrounded by a second furnace, the temperature of which was measured by a thermocouple in the well H ; a McLeod gauge was attached a t I.…”

THE REACTIONS OF ACTIVE NITROGEN WITH NITRIC OXIDE AND NITROGEN DIOXIDE1

“…The saturated hydrocarbons which were investigated include methane, ethane (67,68), propane (69), cyclopropane (70), n-, isoand cyclobutane (71,72) and neo-and cyclopentane (73,74). The major, and sametimes the only nitrogenous product of these reactions was found to be hydrogen cyanide.…”