The gas‐phase pyrolysis of alkyl nitrites. IV. Ethyl nitrite

The rate of decomposition of methyl nitrite (MN) has been studied in the presence of isobutane‐ t ‐BuH‐(167‐200°C) and NO (170‐200°C). In the presence of t ‐BuH (∼0.9 atm), for low concentrations of MN (∼10 −4 M ) and small extents of reaction (4‐10%), the first‐order homogeneous rates of methanol (MeOH) formation are a direct measure of reaction (1) since k 4 ( t ‐BuH) » k 2 (NO): . The results indicate that the termination process involves only {article}{empty}{document}t - Bu\, and\, NO:\,\,t - Bu + NOe{document} products, such that k e ∼ 10 10 M −1 ∼ sec −1 .Under these conditions small amounts of CH 2 O are formed (3‐8% of the MeOH). This is attributed to a molecular elimination of HNO from MN. The rate of MeOH formation shows a marked pressure dependence at low pressures of t ‐BuH. Addition of large amounts of NO completely suppresses MeOH formation. The rate constant for reaction (1) is given by k 1 = 10 15.8°0.6‐41.2°1 /· sec −1 . Since ( E 1 + RT ) and Δ H Δ 1 are identical, within experimental error, both may be equated with D (MeO ‐ NO) = 41.8 + 1 kcal/mole and E 2 = 0 ± 1 kcal/mol. From Δ S 1 1 and A 1 , k 2 is calculated to be 10 10.1°0.6 M −1 · sec −1 , in good agreement with our values for other alkyl nitrites. These results reestablish NO as a good radical trap for the study of the reactions of alkoxyl radicals in particular. From an independent observation that k 6 / k 2 = 0.17 independent of temperature, we conclude that {article}{empty}{document}E₆ = 0 ± 1 kcal/ mol\, and\,\,k₆ = 109.3 M- 1 · sec- 1 : MeO + NO6 CH₂ O + HNO{document} . From the independent observations that k 2 : k 2→ : k 6→ was 1:0.37:0.04, we find that k 2→ = 10 9.7 M −1 ċ sec −1 and k 6→ = 10 8.7 M −1 ċ sec −1 . In addition, the thermodynamics lead to the result In the presence of NO (∼0.9 atm) the products are CH 2 O and N 2 O (and presumably H 2 O) such that the ratio N 2 O/CH 2 O ∼ 0.5. The rate of CH 2 O formation was affected by the surface‐to‐volume ratio s / v for different reaction vessels, but it is concluded that, in a spherical reaction vessel, the CH 2 O arises as the result of an essentially homogeneous first‐order, fourcenter elimination of {article}{empty}{document}HNO: MN5CH₂ O + HNO{document} . The rate of CH 2 O formation is given by k 5 = 10 13.6°0.6‐38.5‐1 /ċ sec −1 .