GAS-PHASE THERMOLYSIS OF N-METHYL-N-PHENYL-TERT-BUTYLSULFENAMIDE AND MORPHOLINYL-TERT-BUTYLSULFENAMIDE

N-Methyl-N-phenyl-tert-butylsulfenamide (MPSA) and morpholinyl-tert-bu tylsulfenamide (MOSA) were thermolyzed in a stirred-flow reactor at te mperatures of 340-390 degrees C and pressures of 7-13 Torr, using tolu ene as carrier gas, at residence times of 0.3-1.3 s. Isobutene was for med in 99% yield through first-order reactions having the following Ar rhenius parameters (A,s(-1), E-a, kJ mol(-1)): MPSA, log A = 12.41 +/- 0.02, E-a = 158.8 +/- 0.2; MOSA, log A = 12.91 +/- 0.22, E-a = 159 +/ - 3. It is proposed that the elimination of isobutene takes place by u nimolecular reaction mechanisms involving polar, four-center cyclic tr ansition states, forming S-unsubstituted thiohydroxylamines as coprodu cts. Thermochemical parameters, estimated by semiempirical AM1 calcula tions, are reported for the latter and for the parent molecules. (C) 1 998 John Wiley & Sons, Ltd.