The thermal oxidation of methylamine

A study has been made of the kinetics of the reaction of gaseous methylamine with oxygen. Since the nitrogen atom is eliminated from the molecule in the course of the oxidation, analysis of the products formed at various stages yields evidence about the reaction mechanism which is not available in the study of hydrocarbons. The variation of oxidation rate with time may be represented by the equation dp/dt ═ B ect + D, and the influence of reactant pressures and of temperature on C and D has been determined. Inert gases do not affect the course of the oxidation, but an increase in surface inhibits the reaction to an extent dependent on the composition of the reactant mixture. Since the later stages of the oxidation are complicated by secondary reactions, the analytical results for the early stages provide the most useful information about the main chemical reactions occurring. The greater part of the combined nitrogen is initially converted to ammonia, but small quantities of nitrogen oxides are also formed. The fact that the concentration of ammonia is lowered and that of nitrogen oxides is raised by increasing oxygen pressure suggests that both products arise from reaction of NH2 radicals with the original reactants. One source of these radicals is probably the breakdown of intermediate peroxides such as NH2CH2—O—O—H, the concentration of which largely controls the rate of reaction. Such a decomposition should give rise to formaldehyde and ammonia in approximately equal amounts. The non-equivalence of these products suggests, however, that the major part of the ammonia is formed in some other way, and it is supposed that peroxide radicals such as NH2CH2—O—O— may, instead of reacting with methylamine to give the peroxide as usually postulated, themselves decompose unimolecularly to give ammonia and carbon monoxide. An attempt is made to construct a simplified theory of the oxidation, to estimate the relative frequencies of some of the proposed reaction stages and hence to calculate certain ratios of velocity constants. The suggested mechanism leads to kinetic relationships in close agreement with those found experimentally.