ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 (∼10-4M) and small extents of reaction (4-10%), the first-order homogeneous rates of methanol (MeOH) formation are a direct measure of reaction (1) since k4(t-BuH) »k2(NO): . The results indicate that the termination process involves only \documentclass{article}\pagestyle{empty}\begin{document}$ t - {\rm Bu\, and\, NO:\,\,}t - {\rm Bu} + {\rm NO\stackrel{e}{\longrightarrow}} $\end{document} products, such that ke ∼ 1010 M-1 ∼ sec-1.Under these conditions small amounts of CH2O are formed (3-8% of the MeOH). This is attributed to a molecular elimination of HNO from MN. The rate of MeOH formation shows a marked pressure dependence at low pressures of t-BuH. Addition of large amounts of NO completely suppresses MeOH formation.The rate constant for reaction (1) is given by k1 = 1015.8°0.6-41.2°1/· sec-1. Since (E1 + RT) and ΔHΔ1 are identical, within experimental error, both may be equated with D(MeO - NO) = 41.8 + 1 kcal/mole and E2 = 0 ± 1 kcal/mol. From ΔS11 and A1, k2 is calculated to be 1010.1°0.6M-1 · sec-1, in good agreement with our values for other alkyl nitrites. These results reestablish NO as a good radical trap for the study of the reactions of alkoxyl radicals in particular. From an independent observation that k6/k2 = 0.17 independent of temperature, we conclude that \documentclass{article}\pagestyle{empty}\begin{document}$ E_6 = 0 \pm 1{\rm kcal}/{\rm mol\, and\,}\,k_6 = 10^{9.3} M^{- 1} \cdot {\rm sec}^{- 1} :{\rm MeO} + {\rm NO}\stackrel{6}{\longrightarrow}{\rm CH}_2 {\rm O} + {\rm HNO} $\end{document}. From the independent observations that k2:k2→: k6→ was 1:0.37:0.04, we find that k2→ = 109.7M-1 ċ sec-1 and k6→ = 108.7M-1 ċ sec-1. In addition, the thermodynamics lead to the result In the presence of NO (∼0.9 atm) the products are CH2O and N2O (and presumably H2O) such that the ratio N2O/CH2O ∼ 0.5. The rate of CH2O formation was affected by the surface-to-volume ratio s/v for different reaction vessels, but it is concluded that, in a spherical reaction vessel, the CH2O arises as the result of an essentially homogeneous first-order, fourcenter elimination of \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm HNO}:{\rm MN\stackrel{5}{\longrightarrow}CH}_{\rm 2} {\rm O} + {\rm HNO} $\end{document}. The rate of CH2O formation is given by k5 = 1013.6°0.6-38.5-1/ċ sec-1.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550090406
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