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

• Published in: European journal of organic chemistry 2024-11, Vol.27 (46), p.n/a
• Main Authors: Santos, Carlos V. P., Mattos, Marcio C. S.
• Format: Article
• Language: English
• Subjects: Alcohol; Alcohol oxidation; Autocatalysis; Benzyl alcohol; Density functional theory; DFT calculations; Dichloromethane; Isotope effect; Kinetics; Nitrogen dioxide; Oxidation; Reaction kinetics; Reaction mechanisms; Substitutes
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202400834

A systematic mechanistic study employing rate constant (kobs) 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)/H2O in 50 % MeCN/CH2Cl2 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‐CF3, 3‐NO2 and 4‐NO2 substituted benzyl alcohols and a fractional rate law (3.25) for benzyl alcohol. The DFT results indicated Cl2, formed in situ from TCCA and HCl. Furthermore, calculations support the kinetic results with high agreement through a transition state that performs a hydride ion by autocatalytic Cl2 in the induction zone. In the case of substrates bearing strong electron withdrawing groups, the mechanism changes to hydrogen ion from the corresponding benzyl hypochlorite as the main pathway. The mechanism for the oxidation of substituted benzyl alcohols with TCCA was elucidated by kinetic measurements and DFT calculations. We found hydride ion by autocatalytic Cl2 as the determining step, while strongly electron withdrawing groups diverted the reaction course to hydrogen ion from the respective organic hypochlorite as a special case.