A Mechanistic Study of the Oxidation of Substituted Benzyl Alcohols with Trichloroisocyanuric Acid

Abstract A systematic mechanistic study employing rate constant ( k obs ) kinetics measurements, linear free‐energy relationship, hydrogen kinetic isotope effect and rate law, as well as the Density Functional Theory (DFT) approach (M06‐2x/6‐311G(d,p)) for the oxidation of diverse substituted benzyl alcohols with trichloroisocyanuric acid (TCCA)/H 2 O in 50 % MeCN/CH 2 Cl 2 at 25.0 °C is present. The kinetic results showed an autocatalytic behavior and a primary kinetic isotope effect (4.22). The linear free‐energy relationship ( σ , ρ =−1.22) indicated a mechanism change for 4‐CF 3 , 3‐NO 2 and 4‐NO 2 substituted benzyl alcohols and a fractional rate law (3.25) for benzyl alcohol. The DFT results indicated Cl 2 , formed in situ from TCCA and HCl. Furthermore, calculations support the kinetic results with high agreement through a transition state that performs a hydride abstraction by autocatalytic Cl 2 in the induction zone. In the case of substrates bearing strong electron withdrawing groups, the mechanism changes to hydrogen abstraction from the corresponding benzyl hypochlorite as the main pathway.