Aromatic Sulfonylation. I. Kinetics and Kinetic Isotope Effects in the Sulfonylation

Abstract p-Toluenesulfonylation of toluene, chlorobenzene and bromobenzene in the presence of aluminum chloride was investigated in methylene chloride at 0–20°C. The rate was equal to k3[TsCl][AlCl3][ArH]. Kinetic hydrogen isotope effects were found for p-deuteriotoluene (kH⁄kD=2.8) and p-deuteriochlorobenzene (kH⁄kD=1.98). Infrared studies indicated that not a sulfonyl cation but TsCl-AlCl3 complex was present in the medium. Substitution took place exclusively at para positions for halobenzenes, but 13.4% ortho and 86.6% para isomers were obtained for toluene. Partial rate factors for para positions were 52.5(PhCH3), 0.224(PhCl) and 0.164(PhBr). A plausible reaction mechanism was proposed, in which the abstraction of proton from the σ-complex was rate-determining.