فهرست نشریات علمی دسترسی آزاد ایران

Model reactions of hydrocarbon oxidation with unbranched chain mechanisms are widely used as kinetic assays to determine rate constants of synthetic and natural antioxidants that scavenge alkyl (R•) and peroxy (RO₂•) radicals. In this work, a model system based on the liquid-phase aerobic oxidation of cumene initiated by benzoyl peroxide (BPO) was employed to evaluate the inhibiting activity of the commercial phenolic antioxidant Lowinox 22IB46 and lemon essential oil (LEO). Before antioxidant testing, the oxidation of cumene was initiated at 333 K under conditions ensuring a kinetic chain length of about 100. The initiation rate and decay rate constant of recrystallized BPO (purified from dichloroethane) were determined using the Rate of Initiated Chain Reaction (RICR) method. The oxidation rate was monitored by measuring oxygen uptake. In the presence of Lowinox 22IB46, the kinetic oxidation curve displayed a clear induction period, characteristic of classical inhibited hydrocarbon oxidation by sterically hindered phenolic antioxidants. This allowed correct determination of kinetic antioxidant parameters. The effective inhibition rate constant (f·nk₇) and total antioxidant activity (A) for Lowinox 22IB46 were found to be 3.4×10⁵ M⁻¹·s⁻¹ and (34 ± 6.0) s⁻¹, respectively. These values are consistent with literature data. The addition of LEO significantly decreased the slope of the oxygen uptake curve, leading to a reduced steady-state oxidation rate without a detectable induction period. The overall antioxidative activity of LEO was determined as A = 80.6%, while the effective inhibition rate constant related to reactions with cumyl radicals at 333 K was k₁[LEO(C)] = (3.1 ± 0.3) ×10⁵ M⁻¹·s⁻¹.