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Published March 1977 | public
Journal Article

The very low-pressure pyrolysis of phenyl methyl sulfide and benzyl methyl sulfide. The enthalpy of formation of the methylthio and phenylthio radicals


The kinetics and mechanisms of the unimolecular decompositions of phenyl methyl sulfide (PhSCH_3) and benzyl methyl sulfide (PhCH_2SCH_3) have been studied at very low pressures (VLPP). Both reactions essentially proceed by simple carbon-sulfur bond fission into the stabilized phenylthio (PhS·) and benzyl (PhCH_2·) radicals, respectively. The bond dissociation energies BDE(PhS-CH_3) = 67.5 ± 2.0 kcal/mol and BDE(PhCH_2-SCH_3) = 59.4 ± 2 kcal/mol, and the enthalpies of formation of the phenylthio and methylthio radicals ΔH°, _(298K)(PhS·, g) = 56.8 ± 2.0 kcal/mol and ΔH°_f, _(298K)(CH_3S·, g) = 34.2 ± 2.0 kcal/mol have been derived from the kinetic data, and the results are compared with earlier work on the same systems. The present values reveal that the stabilization energy of the phenylthio radical (9.6 kcal/mol) is considerably smaller than that observed for the related benzyl (13.2 kcal/mol) and phenoxy (17.5 kcal/mol) radicals.

Additional Information

© 1977 John Wiley & Sons. Received: May 27, 1976, Revised September 7, 1976. This work was supported in part by the National Science Foundation under Grant No. MPS74-18565 and by the Environmental Protection Agency under Grant No. R802288.

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