Gas phase thermolysis of benzyl t ‐butyl sulfide, phenyl t ‐butyl sulfide, and phenyl t ‐butyl ether

The pyrolysis kinetics of the title compounds has been studied in a stirred‐flow reactor over the temperature range 440–530°C and pressures between 5 and 14 torr. Benzyl t ‐butyl sulfide and phenyl t ‐butyl ether formed isobutene as product in over 98% yield, together with the corresponding benzyl thiol and phenol. The benzyl thiol decomposes to a large extent into hydrogen sulfide and bibenzyl. In the pyrolysis of phenyl t ‐butyl sulfide, the hydrocarbon products consisted of 80 ±5% isobutene plus 20% isobutane, while the sulfur containing products were thiophenol and diphenyl disulfide. Order one kinetics was observed for the consumption of the reactants. The first order rate coefficients, based on isobutene production, followed the Arrhenius equations: Benzyl t ‐butyl sulfide:\documentclass{article}\pagestyle{empty}\begin{document}$$k(s^{ - 1}) = 10^{13.82 \pm 0.41} \exp ( - 214 \pm 6{\rm kJ/mol }RT)$$\end{document}Phenyl t ‐butyl sulfide:\documentclass{article}\pagestyle{empty}\begin{document}$$k(s^{ - 1}) = 10^{12.03 \pm 0.39} \exp ( - 188 \pm 6{\rm kJ/mol }RT)$$\end{document}Phenyl t ‐butyl ether:\documentclass{article}\pagestyle{empty}\begin{document}$$k(s^{ - 1}) = 10^{14.30 \pm 0.21} \exp ( - 211 \pm 3{\rm kJ/mol }RT)$$\end{document}For benzyl t ‐butyl sulfide and phenyl t ‐butyl ether, the results suggest a unimolecular mechanism involving polar four center cyclic transition states. For phenyl t ‐butyl sulfide, the t ‐butyl‐sulfur single bond fission mechanism is a parallel, less important process than the complex fission one.