The very‐low‐pressure pyrolysis (VLPP) of n‐propyl nitrate, tert‐butyl nitrite, and methyl nitrite. Rate constants for some alkoxy radical reactions

Abstract

The pyrolysis of n-propyl nitrate and tert-butyl nitrite at very low pressures (VLPP technique) is reported. For the reaction n-PrON02 A nPrO + NO2 the high-pressure rate expression at 300"K, log k, (sec-l) = 16.5 -40.0 kcal/mole/2.3 RT, is derived. The reaction tert-BuONO -% tert-BuO + N O was studied and the high-pressure parameters at 300°K are log kz(sec-') = 15.8 -39.3 kcal/mole/2.3 RT. From aSP,-1 and AS:,-, and the assumption EP1 and E-2 'v 0, we derive log kLl(M-l.sec-l) (300'K) = 9.5 and logIn contrast, the pyrolysis of methyl nitrite and methyld S nitrite afford N O and HIVO and DNO, respectively, in what appears to be a heterogeneous process. The values of k-l and k--5 in conjunction with independent measurements imply a value at 300°K for CHaO + 0 2 CHzO + HO2 of 3.5 X l o 5 M-' .sec-', which is two orders of magnitude greater than currently accepted values.

The decomposition of dimethyl peroxide and the rate constant for CH3O + O2 → CH2O + HO2

“…Combining their result with the ratio k9,/k7, = 2 f I , we find that log k7,(il/l-1.sec-1) = 9.8 f 0.5, where the quoted uncertainty has been derived by a propagation of errors analysis. Thus the uncertainty associated with k7a is far greater than that due to stoichiometry or that due to random experimental errors in the ratio and in t,heirs, the results appear to be remarkably consistent with one another, as well as with recent estimates [20] for the rate constant. Most of these, however, were obtained by using "third-generation" methoxy radicals and a complex reaction mechanism.…”

Stopped‐flow studies of the mechanisms of ozone–alkene reactions in the gas phase propene and isobutene

“…A key number required for the model calculations is the rate constant for the CH30 + 0 2 reaction, for which there are strongly conflicting values. Wiebe and coworkers [16] report a value of k13 = 1.6 X 106 cm3/mol-sec, whereas Mendenhall and co-workers [17] report k13 = 3.5 X 108 cm3/moI-sec. There is no basis for a rational choice for this number at this time, although a recent determination by Barker and co-workers [32] supports the higher value.…”

The reaction of methoxy radicals with nitric oxide and nitrogen dioxide

“…Mendenhall, Golden, and Benson also observed the pressure dependence of reaction (2') [16]. Runs a t different temperatures were carried out using a total pressure of nitrogen of 500 Torr ( Table 111).…”