| Abstract | Thermolysis of 4-aminophenyl benzyl sulfide at 523 K in the hydrogen donor solvent (HDS), 9,10-dihydroanthracene (AnH₂), gave 4-aminothiophenol and toluene as the predominant products of the homolytic S-C bond cleavage. Under these conditions, a portion of the 4-aminothiophenol was desulfurized to aniline with first-order kinetics and with a rate constant estimated by kinetic modeling to be 7.0 X 10⁻⁶ s⁻¹. Starting with 4-NH₂C₆H₄SH at 523 K, it was found that sulfur loss was more efficient in the non-HDSs, anthracene and hexadecane, than in AnH₂. Under similar (competitive) reaction conditions, YC₆H₄SHs with Y = H, 4-CN, and 3-CF₃ were completely inert; with Y = 4-CH₃O, there was some very minor desulfurization, whereas with Y = 4-N(CH₃)₂ and 4-N(CH₃)(H), the sulfur extrusions were as fast as that for Y = 4-NH₂. We tentatively suggest that this apparently novel reaction is a chain process initiated by the bimolecular formation of diatomic sulfur, S₂, followed by a reversible addition of ground state, triplet ³S₂ to the thiol sulfur atom, 4-NH₂C₆H₄S(SS)H, and insertion into the S-H bond, 4-NH₂C₆H₄SSSH. In a cascade of reactions, aniline and S8 are formed with the chains being terminated by reaction of 4-NH₂C₆H₄S(SS)H with 4-NH₂C₆H₄SH. Such a reaction mechanism is consistent with the first-order kinetics. That this reaction is primarily observed with 4-YC₆H₄SH having Y = N(CH₃)₂, N(CH₃)(H), and NH₂ is attributed to the fact that these compounds can exist as zwitterions. |
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