ALBERT

Notes: The kinetics of the Diels-Alder additions of CH2 = CHCN, CH2 = C(CH3) CN, and cis- and trans-CH3CH = CHCN to cyclohexa-1, 3-diene have been studied in the gas phase. The stereochemistry of these reactions is discussed. In terms of a biradical mechanism, a minimum value of 4.1 ± 0.8 kcal mol-1 for the stabilizing effect of a CN group vis-à-vis a methyl group is shown to fit the experimental activation energies.

Notes: The kinetics of the Diels-Alder additions of CH2 — CHCHO, CH2—C(CH3)CHO, and CH2—CHC(CH3)O to cyclohexa-1,3-diene (CHD) have been studied in the gas phase. The stereochemistry and the mechanism of these reactions are discussed. In contrast with other Diels-Alder additions involving CHD as diene, a biradical mechanism does not fit the experimental results.

Notes: The pyrolysis of C2Cl6 has been studied between 652 and 735 K at pressures ranging from 19 to 50 torr. The observed total pressure- and Cl2 pressure-time curves show S-shapes with an induction period depending on temperature and pressure. Further, the total pressure goes through a maximum to finally reach a lower constant value. These curves are explained in terms of a recently proposed reaction model using a parameter optimization computer program. © 1996 John Wiley & Sons, Inc.

Notes: The thermal reaction of 1,3-butadiene (BD) has been studied between 464 and 557°K at pressures between 49 and 450 torr. The products are 4-vinylcyclohexene (VCH) and cis, cis-cycloocta-1,5-diene (COD), and their formations are second order. The rate constant (in 1/mol · sec) for VCH is given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{10} k_{\rm V} = - (24,530 \pm 120)/4.576T + (6.95 \pm 0.05) $$\end{document} and that for COD by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{10} k_{\rm C} = - (28,440 \pm 100)/4.576T + (7.65 \pm 0.04) $$\end{document}The thermal reaction of COD has also been studied. The temperature was varied from 505 to 586°K and the pressure from 15 to 51 torr. The rate constants (in sec-1) for the formations of VCH and BD are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} {\rm log}_{10} k_{{\rm VCH}} = - (51,780 \pm 120)/4.576T + (15.34 \pm 0.05) \\ {\rm log}_{10} k_{{\rm BD}} = - (56,380 \pm 100)/4.576T + (16.46 \pm 0.04) \\ \end{array} $$\end{document}A biradical mechanism seems to fit these results. The heat of formation and the entropy of COD are estimated.

Notes: The addition of ethene to cyclohexa-1,3-diene has been studied between 466 and 591 K at pressures ranging from 27 to 119 torr for ethene and 10 to 74 torr for cyclohexa-1,3-diene. The reaction is of the “Diels-Alder” type and leads to the formation of bicyclo[2.2.2]oct-2-ene. It is homogeneous and first order with respect to each reagent. The rate constant (in l./mol sec) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_a = - (25,970 \pm 50)/4.576{\rm T + }(6.66 \pm 0.02) $$\end{document}The retron-Diels-Alder pyrolysis of bicyclo[2.2.2]oct-2-ene has also been studied. In the ranges of 548-632 K and 4-21 torr the reaction is first order, and its rate constant (in sec-1) is given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log _{10} k_p = - (57,300 \pm 100)/4.576{\rm T + }(15.12 \pm 0.04) $$\end{document}The reaction mechanism is discussed. The heat of formation and the entropy of bicyclo[2.2.2]oct-2-ene are estimated.

Notes: The reactions where Y = CH3 (M), C2H5 (E), i—C3H7 (I), and t—C4H9 (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NMBO}} = - {{\left( {26530 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26530 \pm 80} \right)} {4.576T + \left( {6.05 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.05 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XMBO}} = - {{\left( {28910 \pm 130} \right)} \mathord{\left/ {\vphantom {{\left( {28910 \pm 130} \right)} {4.576T + \left( {6.32 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.32 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NEBO}} = - {{\left( {26150 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {26150 \pm 120} \right)} {4.576T + \left( {5.85 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.85 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XEBO}} = - {{\left( {28560 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {28560 \pm 120} \right)} {4.576T + \left( {6.07 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.07 \pm 0.05} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NIBO}} = - {{\left( {26560 \pm 80} \right)} \mathord{\left/ {\vphantom {{\left( {26560 \pm 80} \right)} {4.576T + \left( {5.57 \pm 0.03} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.57 \pm 0.03} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XIBO}} = - {{\left( {28350 \pm 100} \right)} \mathord{\left/ {\vphantom {{\left( {28350 \pm 100} \right)} {4.576T + \left( {5.47 \pm 0.04} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.47 \pm 0.04} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm NTBO}} = - {{\left( {28920 \pm 50} \right)} \mathord{\left/ {\vphantom {{\left( {28920 \pm 50} \right)} {4.576T + \left( {5.86 \pm 0.02} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {5.86 \pm 0.02} \right)}} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}_{{\rm 10}} k_{{\rm XTBO}} = - {{\left( {32890 \pm 120} \right)} \mathord{\left/ {\vphantom {{\left( {32890 \pm 120} \right)} {4.576T + \left( {6.19 \pm 0.05} \right)}}} \right. \kern-\nulldelimiterspace} {4.576T + \left( {6.19 \pm 0.05} \right)}} $$\end{document} The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.

Notes: Numerical integrations of a hypothetical radical chain reaction model have been performed for the pyrolysis of CH2ClCH3 which is known to be molecular. Analyses of the modelling results have led to a better understanding of the participation (or nonparticipation) of “dead” radicals in the self-inhibition of the radical chain reaction. Attention is focused on the fact that apparently slow elementary reactions still may have to be taken into account in a pyrolysis mechanism when they produce “dead” radicals which can accumulate. © John Wiley & Sons, Inc.

Notes: A detailed radical reaction mechanism is proposed to describe the thermal reactions of CCl4 and C2Cl6 in the gas phase quantitatively.A consistent set of activation energies and preexponential factors for all elementary reactions, in combination with enthalpies of formation and entropies for all species involved, is computer optimized to fit experimental pressure-rise curves and concentration profiles.For this purpose new experimental results on the pyrolysis of CCl4 are used, together with published kinetic data on the pyrolysis of C2Cl6 (in the absence and in the presence of Cl2). © 1996 John Wiley & Sons, Inc.