Pyrolysis of Polycyclic Perhydroarenes. 2. 1-n-Undecylperhydronaphthalene

Abstract

1-n-Undecylperhydronaphthalene (UPN), a prototypical long-chain n-alkylperhydroarene, was pyrolyzed both neat and in benzene in batch microreactors at temperatures between 375 and 475 °C. The global reaction order for UPN disappearance was 1.00 ± 0.08, so UPN pyrolysis followed first-order kinetics. The Arrhenius parameters for the first-order rate constant were A (s -1 ) = 10 10.9 ± 2.6 and E = 46.5 ± 8.4 kcal/mol. All of the reported uncertainties are the 95% confidence intervals. An empirical structure-reactivity correlation in the literature, which was developed for the pyrolysis of saturated cyclic compounds with short n-alkyl chains, did not accurately predict the pyrolysis kinetics of UPN and other long-chain n-alkylperhydroarenes. UPN neat pyrolysis generated numerous primary products, and the primary products with the highest initial selectivities were octahydronaphthalene plus n-undecane, methyleneperhydronaphthalene plus n-decane, and trans-decalin plus 1-undecene. These three product pairs accounted for about 40% of the primary product spectrum from UPN. The remaining 60% was apportioned in roughly equal selectivities among 18 other primary product pairs that consisted of either an n-alkane plus an alkenylperhydronaphthalene or a 1-alkene plus an n-alkylperhydronaphthalene. Secondary reactions included dehydrogenation of decalin and octahydronaphthalene, to form tetralin and eventually naphthalene, and thermal cracking of paraffins, olefins, and other primary products. This product spectrum is consistent with a free radical chain reaction mechanism for UPN neat pyrolysis.