Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The pyrolysis kinetics of RC6H4SS—t—C4H9 (R=H, p-NO2, p-Cl, p-F) were determined at 390-450°C and 7-15 Torr in a stirred-flow reactor using toluene as carrier gas. The reaction products were 95% isobutene, 5% isobutane and the corresponding RC6H4SSH disulphanes. The first-order rate constants, k (s-1), based on isobutene production, followed the Arrhenius equations: phenyl tert-butyl disulphide, k = 1013.49±0.31 exp (- 182 ± 4 kJ mol-1)(RT)-1; pnitrophenyl tert-butyl disulphide, k = 1013.46 ± 0.32 [exp(- 185 ± 5 kJ mol-1)(RT)-1]; p-chlorophenyl tert-butyl disulphide, k = 1014.44 ± 0.66 [exp(- 196 ± 9 kJ mol-1)(RT)-1; p-fluorophenyl tert-butyl disulphide, k = 1010.80 ± 0.16 exp(- 144.5 ± 2 kJ mol -1)(RT)-1]; The observed reactivities, within the above temperature range, follow the order p—F 〉 H 〉 p—Cl 〉 p—NO2. A four-centre, cuadrupolar cyclic transition state mechanism is proposed for the formation of the isobutene and aryldisulphane products. The optimized ground-state molecular geometries of the reactants were calculated by using the MINDO/3 procedure.
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