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

✍ Scribed by A. J. Colussi; S. W. Benson

• Publisher: John Wiley and Sons
• Year: 1977
• Tongue: English
• Weight: 481 KB
• Volume: 9
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550090212

✦ Synopsis

The kinetics and mechanisms of the unimolecular decompositions of phenyl methyl sulfide (PhSCH,) and benzyl methyl sulfide (PhCHzSCH3) have been studied at very low pressures (VLFP). Both reactions essentially proceed by simple carbon-sulfur bond fission into the stabilized phenylthio (PhS. ) and benzyl (PhCH,. ) radicals, respectively. The bond dissociation energies BDE(PhS-CH,) = 67.5 f 2.0 kcal/mol and BI>E(PhCHZ-SCH,) = 59.4 i 2 kcal/mol, and the enthalpies of formation of the phenylthio and methylthio radicals AHo,.,osK(PhS., g) = 56.8 f 2.0 kcaI/mol and A H / ~. ~~~~( C H , S . , g) = 34.2 =k 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.