A kinetic study of the Friedel–Crafts reaction of naphthalene with para-substituted benzenesulphonyl chlorides; the effect of the substituent

Authors:
  • YYYoshihiro Yoshii
    Yoshihiro Yoshii
  • AIAkiyoshi Ito
    Akiyoshi Ito
  • THTsuneaki Hirashima
    Tsuneaki Hirashima
  • SSSeiji Shinkai
    Seiji Shinkai
  • OMOsamu Manabe
    Osamu Manabe
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Abstract
The kinetics of the Friedel–Crafts reaction of naphthalene with para-substituted benzenesulphonyl chlorides have been investigated. The rate constants for equations (i)(formation of the sulphonyl cation) and (ii)(sulphone formation) were determined separately. The effect of the para-substituents on k1 was XC6H4SO2Cl + AlCl3 [graphic omitted] XC6H4SO2 +·AlCl4 –(i), XC6H4SO2 +·AlCl4 –+C10H8 [graphic omitted] XC6H4SO2C10H10H7·AlCl3+ HCl (ii) well expressed by the Yukawa–Tsuno equation, log(k1X/k1H)=ρ1[σ+γ1(ΔσR +)] where ρ1=–2.7 and γ1= 0.4. On the other hand, the effect of the para-substituents on k3(=k1k2/k–1) was expressed by the Brown–Okamoto equation, log (k3X/k3H)=ρ3σ+ where =ρ3=–2.8. Thus, the electron-donating para-substituents gave the greater reaction rates. We concluded that the sulphonyl cation gives large negative ρ values as a result of its high reactivity, and that its low selectivity for α-attack is due to a steric effect. These kinetic results have been rationalised in terms of bifunctional acid–base catalysis in phenylsulphonylation.