The thermal decomposition of diazomethane in the presence of hydrogen

Ab Initio Chemical Kinetics for Singlet CH2 Reaction with N2 and the Related Decomposition of Diazomethane

“…The related thermal decomposition of DM producing 1 CH 2 and N 2 has been experimentally measured by a number of investigators − because it is an important source of the CH 2 radical. In an early static photolysis experiment in the pressure range 40−200 Torr at temperatures between 410 and 490 K, Steacie observed that the decomposition of DM was homogeneous and bimolecular with an activation energy of approximately 36 kcal/mol.…”

“…Setser and Rabinovitch continued to measure this reaction in different conditions and reported k 1 = 1.2 × 10 12 exp(−34 000/ RT ) s −1 in 1:20 mixtures of diazomethane: cis -butene (at a total pressure of 25 Torr in the temperature range 505−530 K). Dunning and McCain obtained k 1 = 0.9 × 10 12 exp(−32 000/ RT ) s −1 in the mixtures of 0.42 Torr DM and 110 Torr hydrogen in the temperature range 566−546 K. Dove and Riddick studied the kinetics and mechanism for the decomposition of DM diluted with krypton in shock waves using the time-of-flight spectrometer and obtained the second-order rate constants, k 1 ′, Kr = 10 9.61±0.21 exp(−15 800 ± 1000/ RT ) 1 mole −1 s −1 at pressures 45−95 Torr in the temperatures 820−1200 K. Here we corrected the units in this expression as l mole −1 s −1 according to the experimental data plotted in their Figures 6 and 7 in l mole s units, not cm 3 mole −1 s −1 given by the authors in the abstract. Otherwise the second-order data can not match the first-order experimental data plotted in their Figure 9 .…”

Mass spectrometric studies of chemical reactions in shock waves. Part II. The thermal decomposition of diazomethane

“…Acetylene has seldom been reported as a product of diazomethane decomposition at lower temperatures, but it has occasionally been detected in both thermal (4,6) and photolytic (1 8) experiments. The absence or low incidence of acetylene under those conditions does not necessarily invalidate our proposed reaction mechanism, since k, is temperature dependent.…”

“…Hence, reaction 6 is 38 kcal mole-' endothermic, and our value of E,' -27 kcal mole-' is reasonable if the reaction is in fact in the second order region. NH radicals are much less reactive than CH, (44) and may event~~ally be removed via However, NH is isoelectronic with CH,, so that reaction 20, the analogue of reaction 2, may occur, the methyIeneimine formed then decomposes to form more HClV 'Hydrogen cyanide has been detected as a product when CH,N, is decomposed in the presence of H, (6). Its formation was attributed to the reaction sequence As already noted, CH, was not detected in the present work, but CHN, could be formed by reaction 9.…”

“…Early experiments by Steacie (2) in a static system in the pressure range Torr and a t temperatures between 410 and 490 OK indicated that the decomposition was homogeneous and bimolecular, with an activation energy of approximately 36 kcal mole-'. However, it has now been established (3)(4)(5)(6) that at temperatures greater than 500 OK the initial step is the unimolecular reaction Torr hydrogen in the range 566-646 OK). Setser and Rabinovitch suggest that their measurements were made in the fall-off region and that their measured activation energy was about 1 kcal mole-' lower than E,.…”