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 XC6H4SO 2Cl + AlCl3 ⇌ k1k-1 XC 6H4SO2+·AlCl4 - (i) XC6H4SO2+· AlCl4- + C10H8 →k2 XC6H4SO2C10H7· 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 phenyl-sulphonylation.
|Number of pages||5|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - 1988|
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